Kubernetes From Scratch .pdf

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Kubernetes From Scratch
By: Eng. Mohamed ElEmam
Email: Mohamed.ElEmam.Hussin@gmail.com

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Kubernetes
What is Kubernetes?
Kubernetes is an open source orchestration tool developed by Google for managing micro-
services or containerized applications across a distributed cluster of nodes.
Kubernetes provides highly resilient infrastructure with zero downtime deployment capabilities,
automatic rollback, scaling, and self-healing of containers (which consists of auto-placement,
auto-restart, auto-replication, and scaling of containers on the basis of CPU usage).
Kubernetes created from Borg & Omega projects by google as they use it to orchestrate they
data center since 2003.
Google open-sourced kubernetes at 2014.
What is Orchestration Do?
 Configuring and scheduling of containers.
 Provisioning and deployments of containers.
 High Availability of containers.
 Configuration of the applications that run in containers.
 Scaling of containers to equally balance the application workloads across infrastructure.
 Allocation of HW resources between containers.
 Load balancing, traffic routing and service discovery of containers.
 Health monitoring of containers.
 Securing the interactions between containers.
Famous Container Orchestrator
 Docker Swarm
 Mesos (Mesos Sphere)

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 Normand
 Cloud Foundry
 Cattel
 Cloud (Azure, Amazon, Google, Alibaba, IBM)
Kubernetes Components and Architecture
 K8s Master Node: the master server that will create the cluster and it has all the
components and service that manage, plan, schedule and monitor all the worker nodes.
 Worker Node: the server that has host the applications as Pods and containers.
 Can make more than master server to make HA for the K8s components
Kubernetes Master Node Components
Below are the main components on the master node:
 API server – is the primary management components of kubernetes and is responsible
for orchestrating all operations (scaling, updates, and so on) in the cluster. It also acts as
the gateway to the cluster, so the API server must be accessible by clients from outside
the cluster integration with CLI and GUI.

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 Controller-manager - The Controller Manager is the engine that runs the core control
loops, create Pods, watches the state of the cluster, and makes changes to drive status
toward the desired state.
 Replication-Controller - A ReplicationController ensures that a specified number of pod
replicas are running at any one time. It makes sure that a pod is always up and available.
 Node Controller - The node controller is a Kubernetes master component which
manages various aspects of nodes.
 Scheduler - is identify the right node to place a container on based resource limitations
or guarantees, taints, tolerations and affinity/anti-affinity roles.
 etcd cluster - etcd is a critical part of the Kubernetes. etcd database that stores the state
of the cluster, including node and workload information in a key/value format.
Add-ons:
 DNS: all Kubernetes clusters should have cluster DNS to resolve name of the containers
inside master node as all the above components is containers inside master node
 Web UI: web-based UI for Kubernetes clusters. It allows users to manage and
troubleshoot applications running in the cluster, as well as the cluster itself.
 Container runtime: The container runtime is the software that is responsible for running
containers. Kubernetes supports several container runtimes: Docker , containerd , CRI-O
Node (worker) components
Below are the main components on a (worker) node:
 kubelet - the main service on a node, connect between Master and Node and ensuring
that pods and their containers are healthy and running in the desired state. This
component also reports to the master on the health of the host where it is running.
 kube-proxy - a proxy service that runs on each worker node to deal with individual host
subnetting and expose services to the external world. It performs request forwarding to
the correct pods/containers across the various isolated networks in a cluster.
Kubectl
kubectl command is a line tool that interacts with kube-apiserver and send commands to the
master node. Each command is converted into an API call.

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Architecture Big Picture: Master Node responsible for the k8s and 4 workers have
the Pods and containers

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Kubernetes Concepts
Making use of Kubernetes requires understanding the different abstractions it uses to represent
the state of the system, such as services, pods, volumes, namespaces, and deployments.
 Pod - generally refers to one or more containers that should be controlled as a single
application.
Pods that run a single container. The "one-container-per-Pod" model is the
most common Kubernetes use case; in this case, you can think of a Pod as a
wrapper around a single container; Kubernetes manages Pods rather than
managing the containers directly.
Pods that run multiple containers that need to work together. A Pod can
encapsulate an application composed of multiple co-located containers that are
tightly coupled and need to share resources. These co-located containers form a
single cohesive unit of service—for example, one container serving data stored in
a shared volume to the public, while a separate sidecar container refreshes or
updates those files. The Pod wraps these containers, storage resources, and an
ephemeral network identity together as a single unit.

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Note: Grouping multiple co-located and co-managed containers in a single Pod
is a relatively advanced use case. You should use this pattern only in specific
instances in which your containers are tightly coupled.
Every Pod has 1 IP address and it has MAC address and we can allocate
resource for it (CPUs, RAM, Network …etc,).
Communication between containers in different Pods via Pods IPs not
container IP.
 Deployment – it provides declarative updates to applications, a deployment allows you
to describe an application’s life cycle, such as which images to use for the app, the
number of pods there should be, and the way in which they should be updated.
Deploy a replica set or pod
Update pods and replica sets
Rollback to previous deployment versions
Scale a deployment
Pause or continue a deployment

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 Service – Allows you to dynamically access a group of replica Pods via IP and Port from
your network and define name for the service.
Pods are volatile, that is Kubernetes does not guarantee a given physical pod will
be kept alive (for instance, the replication controller might kill and start a new set
of pods). Instead, a service represents a logical set of pods and acts as a gateway,
allowing (client) pods to send requests to the service without needing to keep
track of which physical pods actually make up the service.
 Namespace – it’s like resource pool in VMware or tenant in azure, it’s a virtual cluster (a
single physical cluster can run multiple virtual ones)
Intended for environments with many users spread across multiple teams or
projects, for isolation of concerns.
Resources inside a namespace must be unique and cannot access resources in a
different namespace.
Also, a namespace can be allocated a resource quota to avoid consuming more
than its share of the physical cluster’s overall resources (CPU, RAM, and Security).

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 Desired State - describes the desired state of a pod or a replica set, in a yaml file. The
deployment controller then gradually updates the environment (for example, creating or
deleting replicas or replicas image version upgrading or rollback via replication
controller) until the current state matches the desired state specified in the deployment
file. For example, if the yaml file defines 3 replicas for a pod but only two is currently
running (current state), an extra one will get created. Note that replicas managed via a
deployment should not be manipulated directly, only via new deployments.
 Secret - At the application level, Kubernetes secrets can store sensitive information (such
as passwords, SSH keys, API keys or tokens) per cluster (a virtual cluster if using
namespaces, physical otherwise).
Kubernetes Secret can be injected into a Pod container either as an environment
variable or mounted as a file.
Using Kubernetes Secrets allows us to abstract sensitive data and configuration
from application deployment.
Note that secrets are accessible from any pod in the same cluster. Network
policies for access to pods can be defined in a deployment. A network policy
specifies how pods are allowed to communicate with each other and with other
network endpoints.
Note that storing sensitive data in a Kubernetes Secret does not make it secure.
By default, all data in Kubernetes Secrets is stored as a plaintext encoded with
base64.
 CoreDNS - CoreDNS is a flexible, extensible DNS server that can serve as the Kubernetes
cluster DNS. Like Kubernetes, the CoreDNS project is hosted by the CNCF.
You can use CoreDNS instead of kube-dns in your cluster by replacing kube-dns
in an existing deployment, or by using tools like kubeadm that will deploy and
upgrade the cluster for you
 Node-Proxy - a proxy service that runs on each worker node to deal with individual host
subnetting and expose services to the external world. It performs request forwarding to
the correct pods/containers across the various isolated networks in a cluster.
 Replica Set & Deployment - A ReplicaSet is a set of Pod templates that describes a set
of Pod replicas. It uses a template that describes what each Pod must contain.
The ReplicaSet ensures that a specified number of Pod replicas are running at any
time.

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You can define a deployment to create a ReplicaSet or to remove deployments
and adopt all their resources with new deployments. When you revise a
deployment, a ReplicaSet is created that describes the state that you want.
During a rollout, the deployment controller changes the actual state to the state
that you want at a controlled rate. Each deployment revision can also be rolled
back. Deployments can also be scaled.
ReplicaSet is a part of Deployment.
 Daemon Set - Aggregating service logs, collecting node metrics, or running a networked
storage cluster all require a container to be replicated across all nodes. In Kubernetes,
this is done with a DaemonSet.
A DaemonSet ensures that an instance of a specific pod is running on all (or a
selection of) nodes in a cluster. This page gathers resources on how to use and
deploying a daemon to all nodes.
DaemonSet are used to ensure that some or all of your K8S nodes run a copy of a
pod, which allows you to run a daemon on every node.
 Why use DaemonSets?
To run a daemon for cluster storage on each node , such as: glusterd

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To run a daemon for logs collection on each node, such as: logstash
To run a daemon for node monitoring on ever note, such as: collectd
 Label - Labels are key/value pairs that are attached to Kubernetes objects, such as pods
(this is usually done indirectly via deployments).
Labels are intended to be used to specify identifying attributes of objects that are
meaningful and relevant to users.
Labels can be used to organize and to select subsets of objects.
Some labels are required for every deployment resource: (application, version,
release, stage) can add Owner
Contain identifying information and are a used by selector queries or within
selector sections in object definitions.
Example deployment metadata:
Let’s create a pod that initially has one label (stage=production):
# kubectl apply -f https://raw.githubusercontent.com/openshift-
evangelists/kbe/main/specs/labels/pod.yaml
# kubectl get pods --show-labels
NAME READY STATUS RESTARTS AGE LABELS
labelex 1/1 Running 0 10m stage= production

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In above get pods command note the --show-labels option that output the labels
of an object in an additional column.
You can add a label to the pod as:
# kubectl label pods labelex owner= Ahmed
# kubectl get pods --show-labels
NAME READY STATUS RESTARTS AGE LABELS
labelex 1/1 Running 0 16m stage= production,owner= Ahmed
 Selector - let me apply policy on labels
To use a label for filtering and apply policy, for example to list only pods that
have an owner that equals Ahmed, use the --selector option:
# kubectl get pods --selector owner=Ahmed
NAME READY STATUS RESTARTS AGE
labelex 1/1 Running 0 27m
The --selector option can be abbreviated to -l, so to select pods that are labelled
with stage= production, do:
# kubectl get pods -l stage= production
Now, let’s list all pods that are either labelled with stage=development or with
stage =production:
$ kubectl get pods -l stage in (production, development)'
labelexother 1/1 Running 0 3m

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 Annotations - Are used for non-identifying information. Stuff not used internally by
k8s. You can’t specify selectors over them within Kubernetes, but they can be used by
external tools and libraries. As the internal performance of Kubernetes is not negatively
impacted by huge annotations, the keys and values are not constrained like labels.
 Affinity, Anti Affinity - nodeSelector provides a very simple way to constrain pods to
nodes with particular labels. The affinity/anti-affinity feature, greatly expands the types of
constraints you can express. The key enhancements are
The affinity/anti-affinity language is more expressive. The language offers more
matching rules besides exact matches created with a logical AND operation;
You can indicate that the rule is "soft"/"preference" rather than a hard
requirement, so if the scheduler can't satisfy it, the pod will still be scheduled;
You can constrain against labels on other pods running on the node (or other
topological domain), rather than against labels on the node itself, which allows
rules about which pods can and cannot be co-located.
The affinity feature consists of two types of affinity, "node affinity" and "inter-
pod affinity/anti-affinity". Node affinity is like the existing nodeSelector (but
with the first two benefits listed above), while inter-pod affinity/anti-affinity
constrains against pod labels rather than node labels, as described in the third
item listed above, in addition to having the first and second properties listed
above.
 Taints, Tolerations - Taints are used to repel Pods from specific nodes. This is quite
similar to the node anti-affinity, however, taints and tolerations take a slightly different

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approach. Instead of applying the label to a node, we apply a taint that tells a scheduler
to repel Pods from this node if it does not match the taint. Only those Pods that have a
toleration for the taint can be let into the node with that taint.
Tolerations are applied to pods, and allow (but do not require) the pods to
schedule onto nodes with matching taints.
Taints and tolerations work together to ensure that pods are not scheduled onto
inappropriate nodes.
One or more taints are applied to a node; this marks that the node should not
accept any pods that do not tolerate the taints.
You add a taint to a node using kubectl taint. For example,
# kubectl taint nodes node1 key=value:NoSchedule
Above example places a taint on node node1. The taint has key key, value value,
and taint effect NoSchedule. This means that no pod will be able to schedule
onto node1 unless it has a matching toleration.
To remove the taint added by the command above, you can run:
# kubectl taint nodes node1 key:NoSchedule-
Use Cases for Taints and Tolerations: Dedicated node, Nodes with special
hardware
 Config-map - ConfigMaps bind configuration files, command-line arguments,
environment variables, port numbers, and other configuration artifacts to your Pods'
containers and system components at runtime.
ConfigMaps enable you to separate your configurations from your Pods and
components, which helps keep your workloads portable.
Instead of repeat Pods configurations in yaml file for each Pod, We can let the
yaml file read the configuration from ConfigMap file.

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 Volume - similar to a container volume in Docker, but a Kubernetes volume applies to a
whole pod and is mounted on all containers in the pod. Kubernetes guarantees data is
preserved across container restarts. The volume will be removed only when the pod gets
destroyed. Also, a pod can have multiple volumes (possibly of different types) associated.
Kubernetes commands
Overview of kubectl
The kubectl command line tool lets you control Kubernetes clusters. For configuration, kubectl
looks for a file named config in the $HOME/.kube directory. You can specify other kubeconfig
files by setting the KUBECONFIG environment variable or by setting the --kubeconfig flag.
Syntax
kubectl [command] [TYPE] [NAME] [flags]
Where command, TYPE, NAME, and flags are:
 Command: Specifies the operation that you want to perform on one or more resources,
for example create, get, describe, and delete.
 TYPE: Specifies the resource type. Resource types are case-insensitive and you can
specify the singular, plural, or abbreviated forms. For example, the following commands
produce the same output:
 kubectl get pod pod1
 kubectl get pods pod1
 kubectl get po pod1
 NAME: Specifies the name of the resource. Names are case-sensitive. If the name is
omitted, details for all resources are displayed, for example kubectl get pods.
When performing an operation on multiple resources, you can specify each resource by type
and name or specify one or more files:
o To specify resources by type and name:

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 To group resources if they are all the same type: TYPE1 name1 name2
name<#>.
Example: kubectl get pod example-pod1 example-pod2
 To specify multiple resource types individually: TYPE1/name1
TYPE1/name2 TYPE2/name3 TYPE<#>/name<#>.
Example: kubectl get pod/example-pod1 replicationcontroller/example-
rc1
o To specify resources with one or more files: -f file1 -f file2 -f file<#>
 Use YAML rather than JSON since YAML tends to be more user-friendly,
especially for configuration files.
Example: kubectl get pod -f ./pod.yaml
 flags: Specifies optional flags. For example, you can use the -s or --server flags to specify
the address and port of the Kubernetes API server.
Caution: Flags that you specify from the command line override default values and any
corresponding environment variables.
If you need help, just run kubectl help from the terminal window.
Top Commands
#Kubernetes Commands
Helper setup to edit .yaml files with Vim:
 VIM Setup for Yaml files
List of general purpose commands for Kubernetes management:
 PODS
 Create Deployments
 Scaling PODs
 POD Upgrade / History
 Services
 Volumes
 Secrets

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 ConfigMaps
 Ingress
 Horizontal Pod Autoscalers
 Scheduler
 Taints and Tolerations
 Troubleshooting
 Role Based Access Control (RBAC)
 Security Contexts
 Pod Security Policies
 Network Policies
VIM Setup for Yaml files
Put the following lines in ~/.vimrc:
" Yaml file handling
autocmd FileType yaml setlocal ts=2 sts=2 sw=2 expandtab
filetype plugin indent on
autocmd FileType yaml setl indentkeys-=<:>
" Copy paste with ctr+c, ctr+v, etc
:behave mswin
:set clipboard=unnamedplus
:smap <Del> <C-g>"_d
:smap <C-c> <C-g>y
:smap <C-x> <C-g>x
:imap <C-v> <Esc>pi
:smap <C-v> <C-g>p
:smap <Tab> <C-g>1>

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:smap <S-Tab> <C-g>1<
Keyboard hints:
 ctrl + f: auto indent line (requires INSERT mode)
PODS
$ kubectl get pods
$ kubectl get pods --all-namespaces
$ kubectl get pod monkey -o wide
$ kubectl get pod monkey -o yaml
$ kubectl describe pod monkey
Create Deployments
Create single deployment:
$ kubectl run nginx --image=nginx –record
Scaling PODs
$ kubectl scale deployment/POD_NAME --replicas=N
POD Upgrade and history
List history of deployments
$ kubectl rollout history deployment/DEPLOYMENT_NAME
Jump to specific revision
$ kubectl rollout undo deployment/DEPLOYMENT_NAME --to-revision=N
Services
List services
$ kubectl get services
Expose PODs as services (creates endpoints)
$ kubectl expose deployment nginx --port=80 --type=NodePort
Volumes
Lits Persistent Volumes and Persistent Volumes Claims:

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$ kubectl get pv
$ kubectl get pvc
Secrets
$ kubectl get secrets
$ kubectl create secret generic --help
$ kubectl create secret generic mysql --from-literal=password=root
$ kubectl get secrets mysql -o yaml
ConfigMaps
$ kubectl create configmap foobar --from-file=config.js
$ kubectl get configmap foobar -o yaml
DNS
List DNS-PODs:
$ kubectl get pods --all-namespaces |grep dns
Check DNS for pod nginx (assuming a busybox POD/container is running)
$ kubectl exec -ti busybox -- nslookup nginx
Note: kube-proxy running in the worker nodes manage services and set iptables rules to direct
traffic.
Ingress
Commands to manage Ingress for ClusterIP service type:
$ kubectl get ingress
$ kubectl expose deployment ghost --port=2368
Spec for ingress:
 backend
Horizontal Pod Autoscaler
When heapster runs:
$ kubectl get hpa

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$ kubectl autoscale --help
DaemonSets
$ kubectl get daemonsets
$ kubectl get ds
Scheduler
NodeSelector based policy:
$ kubectl label node minikube foo=bar
Node Binding through API Server:
$ kubectl proxy
$ curl -H "Content-Type: application/json" -X POST --data @binding.json
http://localhost:8001/api/v1/namespaces/default/pods/foobar-sched/binding
Tains and Tolerations
$ kubectl taint node master foo=bar:NoSchedule
Troubleshooting
$ kubectl describe
$ kubectl logs
$ kubectl exec
$ kubectl get nodes --show-labels
$ kubectl get events
Docs Cluster:
 https://kubernetes.io/docs/tasks/debug-application-cluster/debug-cluster/
 https://github.com/kubernetes/kubernetes/wiki/Debugging-FAQ
Role Based Access Control
 Role
 ClusterRule
 Binding

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 ClusterRoleBinding
$ kubectl create role fluent-reader --verb=get --verb=list --verb=watch --resource=pods
$ kubectl create rolebinding foo --role=fluent-reader --user=minikube
$ kubectl get rolebinding foo -o yaml
Security Contexts
Docs: https://kubernetes.io/docs/tasks/configure-pod-container/security-context/
 spec
 securityCOntext
o runAsNonRoot: true
Pod Security Policies
Docs:
https://github.com/kubernetes/kubernetes/blob/master/examples/podsecuritypolicy/rbac/READ
ME.md
Network Policies
Network isolation at Pod level by using annotations
$ kubectl annotate ns <namespace> "net.beta.kubernetes.io/network-policy={"ingress":
{"isolation": "DefaultDeny"}}"
More about Network Policies as a resource:
https://kubernetes.io/docs/tasks/administer-cluster/declare-network-policy/
Kubeadm
Kubeadm is a tool built to provide kubeadm init and kubeadm join as best-practice “fast paths”
for creating Kubernetes clusters.
Kubeadm performs the actions necessary to get a minimum viable cluster up and running. By
design, it cares only about bootstrapping, not about provisioning machines. Likewise, installing
various nice-to-have addons, like the Kubernetes Dashboard, monitoring solutions, and cloud-
specific addons, is not in scope.

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Instead, we expect higher-level and more tailored tooling to be built on top of kubeadm, and
ideally, using kubeadm as the basis of all deployments will make it easier to create conformant
clusters.
Kubernetes YAML
As stated on the Wikipedia page for JSON, YAML (Yet Another Markup Language) is a superset
of JSON, which means that it has all the functionality of JSON, but it also extends this
functionality to some degree.
 YAML is basically a wrapper around JSON, doing everything that JSON can do and then
some.
YAML VS JSON
 The YAML file takes less space than the JSON file.
 YAML requires less characters than JSON does.
 YAML allows for comments, while JSON doesn’t.
YAML Syntax
YAML files consist of maps (or dictionaries) of key-value pairs. A YAML map is simply an object,
containing keys and values.
Here’s a map of three key-value pairs:
key1: value1
key2: value2
key3: value3
A single key can itself contain a map:
key1:
subkey1: subvalue1
subkey2: subvalue2
subkey3: subvalue3
YAML also has lists (are just an array of values for a particular key):

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list:
- item1
- item2
- item3
Lists can also contain maps:
list:
- item1
-
mapItem1: value
mapItem2: value
Kubernetes YAML Basics
There are a few required fields in every Kubernetes YAML file to work:
 apiVersion - Which version of the Kubernetes API you're using to create this object
 Kind - What kind of object you want to create
 metadata - Data that helps uniquely identify the object, including a name string, UID,
and optional namespace
 spec - What state you desire for the object
Let’s take another look at our deployment.yaml
apiVersion: v1
kind: pod
metadata:
name: website
labels:
name: web
spec:
containers:
- name: web-server
image: nginx
resources:
limits:
memory: "128Mi"
cpu: "500m"
ports:
- containerPort: 80
apiVersions
Which apiVersion should I use?
Kind apiVersion
CertificateSigningRequest certificates.k8s.io/v1beta1

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ClusterRoleBinding rbac.authorization.k8s.io/v1
ClusterRole rbac.authorization.k8s.io/v1
ComponentStatus v1
ConfigMap v1
ControllerRevision apps/v1
CronJob batch/v1beta1
DaemonSet extensions/v1beta1
Deployment extensions/v1beta1
Endpoints v1
Event v1
HorizontalPodAutoscaler autoscaling/v1
Ingress extensions/v1beta1
Job batch/v1
LimitRange v1
Namespace v1
NetworkPolicy extensions/v1beta1
Node v1
PersistentVolumeClaim v1
PersistentVolume v1
PodDisruptionBudget policy/v1beta1
Pod v1
PodSecurityPolicy extensions/v1beta1
PodTemplate v1
ReplicaSet extensions/v1beta1
ReplicationController v1
ResourceQuota v1
RoleBinding rbac.authorization.k8s.io/v1
Role rbac.authorization.k8s.io/v1
Secret v1
ServiceAccount v1
Service v1
StatefulSet apps/v1
 v1
This was the first stable release of the Kubernetes API. It contains many core objects.
 apps/v1
apps is the most common API group in Kubernetes, with many core objects being drawn
from it and v1. It includes functionality related to running applications on Kubernetes,
like Deployments, RollingUpdates, and ReplicaSets.
 autoscaling/v1
This API version allows pods to be autoscaled based on different resource usage metrics.

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This stable version includes support for only CPU scaling, but future alpha and beta
versions will allow you to scale based on memory usage and custom metrics.
 batch/v1
The batch API group contains objects related to batch processing and job-like tasks
(rather than application-like tasks like running a webserver indefinitely). This apiVersion
is the first stable release of these API objects.
 batch/v1beta1
A beta release of new functionality for batch objects in Kubernetes, notably including
CronJobs that let you run Jobs at a specific time or periodicity.
apiVersion: v1
kind: Pod
metadata:
name: rss-site
labels:
app: web
 When I write that apiversion in YAML file : group/v
APIVersions Reference link https://kubernetes.io/docs/reference/generated/kubernetes-
api/v1.18/#-strong-api-overview-strong-
Kind
What kindly of object you want to create:
To check all kinds available to create:
 # kubectl api-resources

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Hints:
 vsCode is an excellent tool to make the YAML file.
 You can use Helm or Bitnami as chart and ready apps
 You can use container platform and service catalog.
Kubectl Autocomplete
 # source <(kubectl completion bash) # setup autocomplete in bash into the current shell,
bash-completion package should be installed first.
 # echo "source <(kubectl completion bash)" >> ~/.bashrc # add autocomplete
permanently to your bash shell.
Install kubernetes
Step 1 - Kubernetes Installation
The three-node cluster that we will be forming in this example will consist of a Master node and
a Two Slave nodes, therefore, follow the steps described below to install Kubernetes on the
CentOS nodes.
 Kubernetes will be installed as a container so we must install Docker engine

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 All nodes need to have Kubernetes installed on them.
We will prepare all servers for Kubernetes installation by changing the existing configuration on
servers, and also installing some packages, including docker-ce and kubernetes itself.
- Configure Hosts File
 # vim /etc/hosts
Add all servers IPs master and workers to the hosts file below.
 192.168.179.133 k8s-master
 192.168.179.131 node01
 192.168.179.132 node02
Save and exit.
-Configure Firewall
The nodes, containers, and pods need to be able to communicate across the cluster to perform
their functions. Firewalld is enabled in CentOS by default on the front-end. Add the following
ports by entering the listed commands.
On the Master Node enter:
 # firewall-cmd --permanent --add-port=6443/tcp
# firewall-cmd --permanent --add-port=2379-2380/tcp
# firewall-cmd --permanent --add-port=10250/tcp
# firewall-cmd --reload
Enter the following commands on each worker node:
 # firewall-cmd --permanent --add-port=10251/tcp
# firewall-cmd –reload
To list all firewall rules

28
 # firewall-cmd --list-all
Update Iptables Settings
Set the net.bridge.bridge-nf-call-iptables to ‘1’ in your sysctl config file. This ensures that
packets are properly processed by IP tables during filtering and port forwarding.
 # cat <<EOF > /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
sysctl --system
- Enable br_netfilter Kernel Module
The br_netfilter module is required for kubernetes installation. Enable this kernel module so that
the packets traversing the bridge are processed by iptables for filtering and for port forwarding,
and the kubernetes pods across the cluster can communicate with each other.
Run the command below to enable the br_netfilter kernel module.
 # modprobe br_netfilter
 # echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables
-Disable SELinux
 # sudo setenforce 0
 # sudo sed -i ‘s/^SELINUX=enforcing$/SELINUX=permissive/’ /etc/selinux/config
- Disable SWAP
If swap is not disabled, kubelet service will not start on the masters and nodes, for Platform9
Managed Kubernetes version 3.3 and above.
 # swapoff –a
And then edit the '/etc/fstab' file.
Comment the swap line UUID as below.

29
- Install Docker on the nodes
Install the package dependencies for docker-ce.
 # yum install -y yum-utils device-mapper-persistent-data
Add the docker repository to the system and install docker-ce using the yum command.
 # yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-
ce.repo
 # yum install -y docker-ce
- Enable Docker on the nodes
Enable and start the Docker utility on both the nodes by running the following command on
each:
 # systemctl enable docker
 # systemctl start docker
- Add the Kubernetes signing key on the nodes
Add the kubernetes repository and key to the centos 7 system by running the following
command.
 # cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1

30
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOF
- Install Kubeadm
Now install the kubernetes packages kubeadm, kubelet, and kubectl using the yum command
below.
 # yum install -y kubelet kubeadm kubectl
You can check the version number of Kubeadm and also verify the installation through the
following command:
 # kubeadm version
After the installation is complete, restart all those servers.
Log in again to the server and start the services, docker and kubelet.
 # systemctl start docker && systemctl enable docker
 # systemctl start kubelet && systemctl enable kubelet
- Change the cgroup-driver
We need to make sure the docker-ce and kubernetes are using same 'cgroup'.
Check docker cgroup using the docker info command.
 # docker info | grep -i cgroup
And you see the docker is using 'cgroupfs' as a cgroup-driver.
Now run the command below to change the kuberetes cgroup-driver to 'cgroupfs'.
 # sed -i 's/cgroup-driver=systemd/cgroup-driver=cgroupfs/g'
/etc/systemd/system/kubelet.service.d/10-kubeadm.conf
Step 2 - Kubernetes Cluster Initialization
In this step, we will initialize the kubernetes master cluster configuration.

31
Move the shell to the master server 'master' and run the command below to set up the
kubernetes master.
 # kubeadm init --apiserver-advertise-address=10.0.15.10 --pod-network-
cidr=10.244.0.0/16
--apiserver-advertise-address = determines which IP address Kubernetes should advertise its API
server on.
--pod-network-cidr = specify the range of IP addresses for the pod network. We're using the
'flannel' virtual network. If you want to use another pod network such as weave-net or calico,
change the range IP address.
 When the Kubernetes initialization is complete, you will get the result as below.
Copy the 'kubeadm join ... ... ...' command to your text editor. The command will be used to
register new nodes to the kubernetes cluster.
Now in order to use Kubernetes, we need to run some commands as on the result.
Create new '.kube' configuration directory and copy the configuration 'admin.conf'.
 # mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
Next, deploy the flannel network to the kubernetes cluster using the kubectl command.
 # kubectl apply -f
https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-
flannel.yml
The flannel network has been deployed to the Kubernetes cluster.
Wait for a minute and then check kubernetes node and pods using commands below.
 # kubectl get nodes

32
 # kubectl get pods --all-namespaces
And you will get the ‘master' node is running as a 'master' cluster with status 'ready', and you
will get all pods that are needed for the cluster, including the 'kube-flannel-ds' for network pod
configuration.
Make sure all kube-system pods status is 'running'.
Kubernetes cluster master initialization and configuration has been completed.
Step 3 - Adding node1 and node2 to the Cluster
In this step, we will add node1 and node2 to join the 'master' cluster.
Connect to the node1 server and run the kubeadm join command as we copied on the top.
 # kubeadm join 192.168.179.133:6443 --token l12jxw.3c960ner9320dpg8 --discovery-
token-ca-cert-hash
sha256:af54557ca10c0702f6e29bf4d7d96a76eea38e8c85a1bc5cfd6d56ee9d9a1dd7

33
Connect to the node2 server and run the kubeadm join command as we copied on the top.
Wait for some minutes and back to the ‘master' master cluster server check the nodes and pods
using the following command.
 # kubectl get nodes
 # kubectl get pods --all-namespaces
Node1 and Node2 have been added to the kubernetes cluster.
Step 4 - Create First Pod
In this step, we will do a test by deploying the Nginx pod to the kubernetes cluster.
Configure the yaml file of deployment and if want to publish it from external network must to
configure service yaml file
Pod yaml
apiVersion: v1

34
kind: Pod
metadata:
name: website
labels:
name: web
spec:
containers:
- name: web-server
image: nginx
resources:
limits:
memory: "128Mi"
cpu: "500m"
ports:
- containerPort: 80
Service yaml
apiVersion: v1
kind: Service
metadata:
name: Publish-website
spec:
selector:
name: web
type: NodePort
ports:
- name: http
port: 80
targetPort: 80
nodePort: 30003
protocol: TCP
 Above example selector name is the label name on the pod deployment yaml file
 Publish containers from nodeport type use ports from 30000 to 32000.
Create new deployment named 'nginx' using the kubectl command.
 # kubectl create -f website.yaml
To see details of the 'nginx' deployment sepcification, run the following command.
 # kubectl describe deployment nginx

35
Next, we will expose the nginx pod accessible via the internet. And we need to create new
service NodePort for this.
 # kubectl create -f service.yaml
If I want to change anything in yaml configuration and reapply it use command.
 # kubectl apply -f service.yaml
Make sure there is no error. Now check the nginx service nodeport and IP using the kubectl
command below.
 # kubectl get pods
 # kubectl get svc
 # kubectl describe svc
Now you will get the nginx pod is now running under cluster IP address ‘10.109.154.222’ port 80,
and the node main IP address '192.168.179.131' on port '30003'.
The Nginx Pod has now been deployed under the Kubernetes cluster and it's accessible via the
internet, now access from the web browser. http://192.168.179.131:30003/
Kubernetes Namespace

36
What is a Namespace?
You can think of a Namespace as a virtual cluster inside your Kubernetes cluster. You can have
multiple namespaces inside a single Kubernetes cluster, and they are all logically isolated from
each other. They can help you and your teams with organization, security, and even
performance!
In most Kubernetes distributions, the cluster comes out of the box with a Namespace called
“default.” In fact, there are actually three namespaces that Kubernetes ships with: default, kube-
system (used for Kubernetes components), and kube-public (used for public resources). Kube-
public isn’t really used for much right now, and it’s usually a good idea to leave kube-system
alone
Functionality of Namespace
Following are some of the important functionalities of a Namespace in Kubernetes −
 Namespaces help pod-to-pod communication using the same namespace.
 Namespaces are virtual clusters that can sit on top of the same physical cluster.
 They provide logical separation between the teams and their environments.
Create a Namespace
The following command is used to create a namespace.
apiVersion: v1
kind: Namespace
metadata
name: MicroFinance
Control the Namespace
The following command is used to control the namespace.
# kubectl create –f namespace.yml ---------> 1
# kubectl get namespace -----------------> 2
# kubectl get namespace <Namespace name> ------->3
# kubectl describe namespace <Namespace name> ---->4
# kubectl delete namespace <Namespace name>
In the above code,
 We are using the command to create a namespace.

37
 This will list all the available namespace.
 This will get a particular namespace whose name is specified in the command.
 This will describe the complete details about the service.
 This will delete a particular namespace present in the cluster.
This is a sample resource quota limit for namespace
apiVersion: v1
kind: ResourceQouta
metadata:
name: compute-qouta
namespace: prod
spec:
hard:
pods: "10"
requests.cpu: "4"
requests.memory: 5Gi
limits.cpu: "10"
limits.memory: 10Gi
This is the output after apply limits on namespace
 # kubectl describe namespace prod
Using Namespace in Service - Example
Following is an example of a sample file for using namespace in service.
apiVersion: v1

38
kind: Service
metadata:
name: Micro
namespace: MicroFinance
labels:
component: Micro
spec:
type: LoadBalancer
selector:
component: Micro
ports:
- name: http
port: 9200
protocol: TCP
- name: transport
port: 9300
protocol: TCP
In the above code, we are using the same namespace under service metadata with the name of
MicroFinance.
Kubernetes Deployments
Deployments are upgraded and higher version of replication controller. They manage the
deployment of replica sets which is also an upgraded version of the replication controller. They
have the capability to update the replica set and are also capable of rolling back to the previous
version.
They provide many updated features of matchLabels and selectors. We have got a new
controller in the Kubernetes master called the deployment controller which makes it happen. It
has the capability to change the deployment midway.
Changing the Deployment

39
 Updating − The user can update the ongoing deployment before it is completed. In this,
the existing deployment will be settled and new deployment will be created.
 Deleting − The user can pause/cancel the deployment by deleting it before it is
completed. Recreating the same deployment will resume it.
 Rollback − We can roll back the deployment or the deployment in progress. The user
can create or update the deployment by using DeploymentSpec.PodTemplateSpec =
oldRC.PodTemplateSpec.
Deployment Strategies
Deployment strategies help in defining how the new RC should replace the existing RC.
Recreate − This feature will kill all the existing RC and then bring up the new ones. This results
in quick deployment however it will result in downtime when the old pods are down and the
new pods have not come up.
Rolling Update − This feature gradually brings down the old RC and brings up the new one.
This results in slow deployment, however there is no deployment. At all times, few old pods and
few new pods are available in this process.
The configuration file of Deployment looks like this.
apiVersion: extensions/v1beta1 --------------------->1
kind: Deployment --------------------------> 2
metadata:
name: Tomcat-ReplicaSet
spec:
replicas: 3
template:
metadata:
lables:
app: Tomcat-ReplicaSet
tier: Backend
spec:
containers:
- name: Tomcatimage:
tomcat: 8.0
ports:
- containerPort: 7474
In the above code, the only thing which is different from the replica set is we have defined the
kind as deployment.

40
Create Deployment
 # kubectl create –f Deployment.yaml –record
-–record to see the deployments by command # kubectl rollout status deployment/Deployment
Deployment "Deployment" created successfully.
Fetch the Deployment
 # kubectl get deployments
 # kubectl get deploy -o wide
NAME DESIRED CURRENT UP-TO-DATE AVILABLE AGE
Deployment 3 3 3 3 20s
Check the Status of Deployment
 # kubectl rollout status deployment/Deployment
Updating the Deployment
 # kubectl apply –f Deployment.yaml (after update the new version inside the yaml file)
 # kubectl set image deployment/Deployment tomcat=tomcat:6.0
Rolling Back to Previous Deployment
 # kubectl rollout undo deployment/Deployment –to-revision=2
Check rollout history
 # kubectl rollout history deployment/Deployment
Get ReplicaSet
 # kubectl get replicaset
[root@master ~]# kubectl get replicaset
NAME DESIRED CURRENT READY AGE
Tomcat-ReplicaSet 3 3 3 2d14h

41
Delete ReplicaSet (it will also delete all underlying Pods)
 # kubectl delete ReplicaSet < ReplicaSet name>
[root@master ~]# delete replicaset Tomcat-ReplicaSet
Scaling the Deployment
 # kubectl scale --replicas=6 –f Deployment.yaml
To deploy from local image include imagePullPolicy: Never in the deployment yaml file
spec:
containers:
- name: nginx-web
image: nginx
resources:
limits:
memory: "100Mi"
cpu: "100m"
imagePullPolicy: Never
Assign Pods to Nodes
1- Assign label to your nodes
List the nodes in your cluster, along with their labels:
 # kubectl get nodes --show-labels
Chose one of your nodes, and add a label to it:
 # kubectl label nodes centos type=Master
Verify that your chosen node has a type=Master label:
2- In the YAML file add selector of nodeSelector with the label
spec:
containers:
- name: nginx
image: nginx
nodeSelector:

42
type: Master
Apply your deployment
 # kubectl apply -f Deployment.yaml
To get into Pod Shell
 # kubectl exec --stdin --tty <Pod Name> -- /bin/bash
[root@master ~]# kubectl exec --stdin --tty pod/nginx-deployment-597fbc7d6f-
jhwf2 -- /bin/bash
root@nginx-deployment-597fbc7d6f-jhwf2:/# ls
Kubernetes Networking
Networking in any architecture or technology is very essential to understand if you want to
deploy the applications over the network and also understanding how the network works that
will help you to troubleshoot if you have any network issue. So we must know exactly what is
happening in the network and how all the connections are establishing for the communication
over the network.
This is a basic kubernetes architecture where you have some worker nodes, and few pods are
running on it with couple of containers. When you have these many components, how all these
components are establishing its connection to make the application accessible over the
network? The answer is that happens only through kubernetes networking.
Types of Kubernetes Networking

43
1. Container to Container Communication:
When you have one or more containers within a pod that shares the same host networking. So
pods will get its own IP address, all container shares same ip address but it works on different
port. Communication between containers happens within the pod itself on different port. So all
containers will be able to communicate each other by default.
2. Pod to Pod communication:
As said earlier, each pods will get its own ip address. There are sub types within Pod to Pod
communication, that is.
Intra-node Pod Network - Communication of pods running on a single node.
Inter-node Pod Network - Communication of pods running in different nodes.
On the first case, each pod running on single worker node will have the communication by
default, because all ip address of pods will be different and assigned from your local network.
Since it shares the same host.
On the second case, when you have pod running on multiple worker nodes, communication
between these pods happens through network plugin that will create some route tables. It
forwards the traffic from any pod to any destination pods.
3. Pod to Service Communication:
Service is kubernetes resource type that expose our application to outside the cluster. Through
which pod can send the traffic to services.
4 External to Service Communication:
In order to access our application from outside the cluster, external traffic should be allowed to
reach the server within the cluster... This can be achieved using these different types.
a. ClusterIP
b. NodePort
c. LoadBalancer
d. Extername
Each types has its own function and purpose.
Cluster IP - It is the default kubernetes service used for internal communication within the

44
cluster.
NodePort - It will open a ports on each nodes and traffic will be forwarded to the service
through random port. And I can access the service (Pod) with the node IP + Defined port.
LoadBalancer - It is a type that forwards all external traffic to a service through this type. And I
can access the service (Pod) with the node name only.
External Name - it is a type used to access a service internally that is hosted outside cluster
through DNS CName or A record...
 LoadBalancer service is not in kubernetes by default, to use it we must create ingress
network.
Ingress Policy
Ingress exposes HTTP and HTTPS routes from outside the cluster to services within the cluster.
Traffic routing is controlled by rules defined on the Ingress resource.
internet
|
[ Ingress ]
--|-----|--
[ Services ]
An Ingress may be configured to give Services externally-reachable URLs, load balance traffic,
terminate SSL / TLS, and offer name based virtual hosting.
 An Ingress controller is responsible for fulfilling the Ingress, usually with a load
balancer, though it may also configure your edge router or additional frontends to help
handle the traffic.
 An Ingress does not expose arbitrary ports or protocols. Exposing services other than
HTTP and HTTPS to the internet typically uses a service of type Service.Type=NodePort
or Service.Type=LoadBalancer.

45
Prerequisites
 You must have an ingress controller to satisfy an Ingress. Only creating an Ingress
resource has no effect.
 You may need to deploy an Ingress controller such as ingress-nginx.
The Ingress Resource
A minimal Ingress resource example:
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: test-ingress
namespace: critical-space
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /
spec:
rules:
- http:
paths:
- path: /website
backend:
serviceName: website-service
servicePort: 80
Then I make deployment with type LoadBalancer
apiVersion: v1
kind: Service
metadata:
name: mywebsite
spec:
ports:
-
name: http
port: 80
protocol: TCP
targetPort: 80
type: LoadBalancer
selector:

46
name: mywebsite
Ingress and egress
The bulk of securing network traffic typically revolves around defining egress and ingress rules.
From the point of view of a Kubernetes pod, ingress is incoming traffic to the pod, and egress is
outgoing traffic from the pod. In Kubernetes network policy, you create ingress and egress
“allow” rules independently (egress, ingress, or both).
Kubernetes NodePort vs LoadBalancer vs Ingress? When should I use
what?
They are all different ways to get external traffic into your cluster
ClusterIP
A ClusterIP service is the default Kubernetes service. It gives you a service inside your cluster that
other apps inside your cluster can access. There is no external access.
The YAML for a ClusterIP service looks like this:
apiVersion: v1
kind: Service
metadata:
name: my-internal-service
spec:
selector:
app: my-app
type: ClusterIP
ports:
- name: http
port: 80
targetPort: 80
protocol: TCP
If you can’t access a ClusterIP service from the internet, Turns out you can access it using the
Kubernetes proxy!

47
Start the Kubernetes Proxy:
kubectl proxy --port=8080
Now, you can navigate through the Kubernetes API to access this service using this scheme:
http://localhost:8080/api/v1/proxy/namespaces/<NAMESPACE>/services/<SERVICE-
NAME>:<PORT-NAME>/
So to access the service we defined above, you could use the following address:
http://localhost:8080/api/v1/proxy/namespaces/default/services/my-internal-service:http/
When would you use this?
There are a few scenarios where you would use the Kubernetes proxy to access your services.
 Debugging your services, or connecting to them directly from your laptop for some
reason
 Allowing internal traffic, displaying internal dashboards, etc.
Because this method requires you to run kubectl as an authenticated user, you should NOT use
this to expose your service to the internet or use it for production services.
NodePort
A NodePort service is the most primitive way to get external traffic directly to your service.
NodePort, as the name implies, opens a specific port on all the Nodes (the VMs), and any traffic
that is sent to this port is forwarded to the service.

48
The YAML for a NodePort service looks like this:
apiVersion: v1
kind: Service
metadata:
name: my-nodeport-service
spec:
selector:
app: my-app
type: NodePort
ports:
- name: http
port: 80
targetPort: 80
nodePort: 30036
protocol: TCP
NodePort service has two differences from a normal “ClusterIP” service.
First, the type is “NodePort.” There is also an additional port called the NodePort that specifies
which port to open on the nodes. If you don’t specify this port, it will pick a random port. Most
of the time you should let Kubernetes choose the port; there are many caveats to what ports are
available for you to use.
There are many downsides to this method:
 You can only have one service per port
 You can only use ports 30000–32767
 If your Node/VM IP address change, you need to deal with that
For these reasons, I don’t recommend using this method in production to directly expose your
service. If you are running a service that doesn’t have to be always available, or you are very cost
sensitive, this method will work for you. A good example of such an application is a demo app
or something temporary.

49
LoadBalancer
A LoadBalancer service is the standard way to expose a service to the internet. This will spin up a
Network Load Balancer that will give you a single IP address that will forward all traffic to your
service.
If you want to directly expose a service, this is the default method. All traffic on the port you
specify will be forwarded to the service. There is no filtering, no routing, etc. This means you can
send almost any kind of traffic to it, like HTTP, TCP, UDP, Websockets, gRPC, or whatever.
The big downside is that each service you expose with a LoadBalancer will get its own IP
address, and you have to pay for a LoadBalancer per exposed service, which can get expensive!
Ingress
Unlike all the above examples, Ingress is actually NOT a type of service. Instead, it sits in front of
multiple services and act as a “smart router” or entry point into your cluster.
You can do a lot of different things with an Ingress, and there are many types of Ingress
controllers that have different capabilities.

50
The YAML for an Ingress object with a L7 HTTP Load Balancer might look like this:
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: my-ingress
spec:
backend:
serviceName: other
servicePort: 8080
rules:
- host: foo.mydomain.com
http:
paths:
- backend:
serviceName: foo
servicePort: 8080
- host: mydomain.com
http:
paths:
- path: /bar/*
backend:
serviceName: bar
servicePort: 8080
Ingress is probably the most powerful way to expose your services, but can also be the most
complicated. There are many types of Ingress controllers, from the Google Cloud Load Balancer,
Nginx, Contour, Istio, and more. There are also plugins for Ingress controllers, like the cert-
manager, that can automatically provision SSL certificates for your services.
Ingress is the most useful if you want to expose multiple services under the same IP address,
and these services all use the same L7 protocol (typically HTTP). You only pay for one load
balancer if you are using the native GCP integration, and because Ingress is “smart” you can get
a lot of features out of the box (like SSL, Auth, Routing, etc).

51
Kubernetes Storage
 Persistent volume claim (PVC)
A Persistent Volume Claim (PVC) is a claim request for some storage space by users.
 Persistent volume (PV)
A Persistent Volume (PV) is a piece of storage in the cluster that has been provisioned by
an administrator or dynamically provisioned using Storage Classes.
In simple words, Persistent Volume is a solution to store data of our containers
permanently even after the pods got deleted.
How it is different from other kubernetes volume types?
Let’s say you have multiple pod running on different nodes and you used hostpath volume type.
Your data written by pod 1 running on worker node 1 will be resides only on worker node 1 and
that cannot be access by pod 2 running on worker node 2. Similarly pod 1 cannot access data
written by pod 2 on worker node 2. Right? Since hostpath is a type that writes data only on your
local node directory. It’s not kind of a shared volume.
Other example is, let’s say you have one pod running on worker node1 and your pod written
some data now on local worker node1.

52
But Due to some reasons your pod is rescheduled to run on worker node 2, how about your
data written on worker node1? Your pod will be running on worker node 2 now, but your data
won’t be available here on worker node 2 since your data written by pod1 exists only on worker
node1.
So we must have shared volume that should be accessible across all worker nodes only when
pods need it. In this case, persistent volume and persistent volume claim can be used at the
kubernetes cluster level.
But there is a traditional method to have shared volume across worker nodes at operating
system level by mounting some volume through nfs, fc, iscsi on all worker nodes that can share
the same volume. This example is discussed in the previous article.
Before I explain you how to create persistent volume and persistent volume claim, Let me
explain you what is actually happening in persistent volume and how it works?
In a legacy infrastructure environment, when you need additional storage space to your server,
you will reach out to the storage administrator for the space. So there would be a storage
administrator who allocates some storage space from storage device to your server as you
requested. Similarly, in kubernetes. Persistent volume is a resource type through which you can

53
get your storage space allocated to your kubernetes cluster. Let's say you got some 10G
persistent volume allocated to your kubernetes cluster. Obviously that should be through any
one of the kubernetes volume types. Might be through ISCSI, FC, NFS, or any other cloud
providers. From which you can claim some space you want for your pod using persistent volume
claim. Let's say you want 5 GB for your pod. You can use persistent volume claim to request 5
GB space from your persistent volume. Now you persistent volume will allocates the space you
requested using persistent volume when it is find suitable, now you can use that volume claim in
your deployment.
Let’s see how to create Persistent Volume.
 Create a yaml file for persistent volume to get the storage space for our kubernetes
cluster.
 Create a yaml file to claim the space using peristent volume claim as per our
requirement.
 Define the persistent volume claim in your pod deployment file.
Already I have a single pod running on worker node 1 with two containers. Sample deployment
file is given below. It doesn’t have any volume specification. Let's see how to use persistent
volume and claim.
kind: Deployment
apiVersion: apps/v1
metadata:
name: ebay-app
spec:
selector:
matchLabels:
environment: dev
app: ebay
replicas: 1
template:
metadata:
labels:
environment: dev

54
app: ebay
spec:
containers:
- name: container1-nginx
image: nginx
- name: container2-tomcat
image: tomcat
I have an nfs server that acts as a storage and exported a volume named /nfsdata from
192.168.1.7. Traditional way is to mount the share in all worker nodes, instead we will be using
this share through persistent volume. Right. So create a persistent volume yaml file.
#cat nfs_pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: ebay-pv
spec:
capacity:
storage: 20Gi
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Recycle
storageClassName: ebaystorage
mountOptions:
- nfsvers=4.1
nfs:
path: /nfsdata
server: 192.168.1.7
Persistent Volume supports three types of Reclaim Policy
 Retain
 Delete
 Recycle
Persistent Volume supports three types of access modes
 ReadWriteOnce
 ReadOnlyMany
 ReadWriteMany
Let’s apply the changes and verify it.
user1@kubernetes-master:~/codes/pv$ kubectl apply -f nfs_pv.yaml
persistentvolume/ebay-pv created
user1@kubernetes-master:~/codes/pv$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM
POLICY STATUS CLAIM STORAGECLASS REASON AGE

55
ebay-
pv 20Gi RWO Recycle Available ebaystora
ge 24s
Above output shows that pv "ebay-pv" is created as expected and it is available for claim.
Let’s create persistent volume claim:
user1@kubernetes-master:~/codes/ebay$ cat pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: myclaim
spec:
storageClassName: ebaystorage
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 20G
Claim can be given from kubernetes cluster only when it finds suitable any Storageclassname
and accessmode are same as specified in this claim file, if any persistent volume doesn’t have
these storageclassname or accessmode, then persistent volume claim will not be processed.
Let’s apply this and verify it.
user1@kubernetes-master:~/codes/ebay$ kubectl apply -f pvc.yaml
persistentvolumeclaim/myclaim created
user1@kubernetes-master:~/codes/ebay$ kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
myclaim Bound ebay-pv 20Gi RWO ebaystorage 15s
So our claim is validated and allocated for us.
Now we can use this claim to our pods. Edit your deployment file as below to define the volume
specification. I will be using this volume only for my first container.
user1@kubernetes-master:~/codes/ebay$ cat httpd-basic-deployment.yaml
kind: Deployment
apiVersion: apps/v1
metadata:
name: ebay-app
spec:
selector:
matchLabels:
environment: dev
app: ebay

56
replicas: 1
template:
metadata:
labels:
environment: dev
app: ebay
spec:
volumes:
- name: myvolume
persistentVolumeClaim:
claimName: myclaim
containers:
image: nginx
volumeMounts:
- name: myvolume
mountPath: "/tmp/persistent"
image: tomcat
Just apply the changes.
user1@kubernetes-master:~/codes/ebay$ kubectl apply -f httpd-basic-
deployment.yaml
deployment.apps/ebay-app configured
Use "describe" option to find the volume parameters and confirm the claim is successful. it
should looks like this.
user1@kubernetes-master:~/codes/ebay$ kubectl describe pods ebay-app
........trimmed some content......
Volumes:
myvolume:
Type: PersistentVolumeClaim (a reference to a PersistentVolumeClaim
in the same namespace)
ClaimName: myclaim
ReadOnly: false
default-token-2tqkb:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-2tqkb
Optional: false
........trimmed some content......
That’s it, we have successfully created persistent volume persistent volume claim. Now when
your pod is rescheduled to other worker node, your data will be still available.
Kubernetes Volumes
What is Kubernetes Volumes?
Kubernetes Volumes are used to store data that should be accessible across all your containers
running in a pod based on the requirement.

57
What are the types of Kubernetes Volumes?
Kubernetes supports many kind of storage types, these are determined by how it is created and
assigned to pods.
Local Node Types - emptyDIR, hostpath, local
File Sharing types - nfs
Storage types - fc, iscsi
Special Purpose Types - Secret, Git repo
Cloud Provider types - Vsphere, Cinder, awsElasticBlockStore, azureDisk, gcepersistentDisk
Distributed filesystem types - glusterfs, cephfs
Special type - persistent volume, persistent volume claim
Note:
 emptyDIR - It’s a type of storage types that writes data only in memory till the pods
running. So you data will be erased when the pod is deleted. So it’s not a persistent kind
of types.
 hostpath, local, fc and other types are persistent kind only, but volume won’t be
available across the nodes. It will be available only on local nodes. So we may need to
setup something shared volume using traditional storage mount across all the nodes.
 Persistent volume type volumes can be accessible across all the nodes.
How to use kubernetes volumes to pod and containers?
Use an option "Volumes" along with name and types as below in a deployment file for the entire
PODS and use the "volumeMounts" along with mountPath where the volume to be mounted for
the container. We must use the volume name unique and exactly as specified in specification for
the containers. If not you will end up with error.
Example:
spec:
volumes:
- name: volume
hostPath:
path: /mnt/data
containers:
image: nginx
volumeMounts:
- name: volume
mountPath: "/var/nginx-data"
image: tomcat

58
Above example tells that, volume name "volume" specified in "spec" section with Path
"/mnt/data" will be used as a volume for this entire pod. It will be mounted only on container
"container1-nginx" since it is claimed to be mounted on path "/var/nginx-data" using
"volumeMounts" option.
How to assign a single volume to specific container in a pod?
In order to use a volume only to specific container running in a pod, we must use volume
mounts option. So that particular container will use the volume specified in spec.
kind: Deployment
apiVersion: apps/v1
metadata:
name: ebay-app
spec:
selector:
matchLabels:
environment: dev
app: ebay
replicas: 1
template:
metadata:
labels:
environment: dev
app: ebay
spec:
volumes:
- name: volume
hostPath:
path: /mnt/data
containers:
image: nginx
volumeMounts:
- name: volume
image: tomcat

59
So we have claimed the volume name "volume" from specification and mapped to the container
"container1-nginx" that would mount the volume under "/var/nginx-data", this volume will be
only available to the first container "container1-nginx" not to the second container "container2-
tomcat". This is how we can assign a single volume to specific container in a pod.
How to share a same volume to all containers within a pod?
In order to share a same volume to all containers running in a pod, we must use volume mounts
option in all containers.
kind: Deployment
apiVersion: apps/v1
metadata:
name: ebay-app
spec:
selector:
matchLabels:
environment: dev
app: ebay
replicas: 1
template:
metadata:
labels:
environment: dev
app: ebay
spec:
volumes:
- name: volume
hostPath:
path: /mnt/data
containers:
image: nginx
volumeMounts:
- name: volume

60
image: tomcat
volumeMounts:
- name: volume
mountPath: "/var/tomcat-data"
This time, we have used volumeMount option for both containers with different path, as per the
code definition, same volume "volume" will be mount on both containers in path "/var/nginx-
data" on container1-nginx and "/var/tomcat-data" on container2-tomcat respectively.
How to assign a dedicated volumes to each container in a pod?
In order to assign a dedicated volumes to each containers running in a pod, we must use
volumes and volumemounts option in all containers accordingly as per the example given
below.
kind: Deployment
apiVersion: apps/v1
metadata:
name: ebay-app
spec:
selector:
matchLabels:
environment: dev
app: ebay
replicas: 1
template:
metadata:
labels:
environment: dev
app: ebay
spec:
volumes:
- name: volume1
hostPath:
path: /mnt/data1
- name: volume2

61
hostPath:
path: /mnt/data2
containers:
image: nginx
volumeMounts:
- name: volume1
image: tomcat
volumeMounts:
- name: volume2
mountPath: "/var/tomcat-data"
As per the above example, volume1 will be used by the first container "container1-nginx" and
volume2 will be used by the second container "container2-tomcat". This is how we can assign
dedicated volumes to each containers running in a pod.
How to assign a shared volume across all pods running on different worker nodes?
Why do we actually need this setup is, so far we have seen volumes that is used only on single
pod running on one worker node. So your data won’t be available when pod is rescheduled to
other node since your hostpath you have used is local directory. If you want your data to be
available for all worker nodes, we must have shared volumes concepts to overcome such
situation. We can use a special type ie PersistentVolume and PersistentVolumeClaim or our
traditional approach that mount a shared volume from storage and use that mounted path in
the deployment file. You can checkout this video for the traditional approach and will explain
you about persistentvolume and persistentvolume claim in the next article.
To get all persistent volumes
 # kubectl get persistentvolume
To get all persistent volumes Claims
 # kubectl get persistentvolumeclaims -o wide

62
Kubernetes Security
Role-Based Access Control (RBAC)
In order to fully grasp the idea of RBAC, we must understand that three elements are involved:
 Subjects: The set of users and processes that want to access the Kubernetes API.
 Resources: The set of Kubernetes API Objects available in the cluster. Examples include
Pods, Deployments, Services, Nodes, and PersistentVolumes, among others.
 Verbs: The set of operations that can be executed to the resources above. Different
verbs are available (examples: get, watch, create, delete, etc.), but ultimately all of them
are Create, Read, Update or Delete (CRUD) operations.
With these three elements in mind, the key idea of RBAC is the following:
We want to connect subjects, API resources, and operations. In other words, we want to specify,
given a user, which operations can be executed over a set of resources.
So, if we think about connecting these three types of entities, we can understand the different
RBAC API Objects available in Kubernetes.
 Roles: Will connect API Resources and Verbs. These can be reused for different subjects.
These are binded to one namespace (we cannot use wildcards to represent more than
one, but we can deploy the same role object in different namespaces). If we want the
role to be applied cluster-wide, the equivalent object is called ClusterRoles.

63
 RoleBinding: Will connect the remaining entity-subjects. Given a role, which already
binds API Objects and verbs, we will establish which subjects can use it. For the cluster-
level, non-namespaced equivalent, there are ClusterRoleBindings.
In the example below, we are granting the user jsalmeron the ability to read, list and create pods
inside the namespace test. This means that jsalmeron will be able to execute these commands:
But not these:
Example yaml files:

64
Another interesting point would be the following: now that the user can create pods, can we
limit how many? In order to do so, other objects, not directly related to the RBAC specification,
allow configuring the amount of resources: ResourceQuota and LimitRanges. It is worth
checking them out for configuring such a vital aspect of the cluster.
Users and… ServiceAccounts?
One topic that many Kubernetes users struggle with is the concept of subjects, but more
specifically the difference between regular users and ServiceAccounts. In theory it looks simple:
 Users: These are global, and meant for humans or processes living outside the cluster.
 ServiceAccounts: These are namespaced and meant for intra-cluster processes running
inside pods.
Both have in common that they want to authenticate against the API in order to perform a set of
operations over a set of resources (remember the previous section), and their domains seem to
be clearly defined. They can also belong to what is known as groups, so a RoleBinding can bind
more than one subject (but ServiceAccounts can only belong to the “system:serviceaccounts”
group). However, the key difference is a cause of several headaches: users do not have an
associated Kubernetes API Object. That means that while this operation exists:
This one doesn’t:
This has a vital consequence: if the cluster will not store any information about users, then, the
administrator will need to manage identities outside the cluster. There are different ways to do
so: TLS certificates, tokens, and OAuth2, among others.
In addition, we would need to create kubectl contexts so we could access the cluster with these
new credentials. In order to create the credential files, we could use the kubectl config
commands (which do not require any access to the Kubernetes API, so they could be executed
by any user). Watch the video above to see a complete example of user creation with TLS
certificates.
Possible operations over these resources are:

65
 create
 get
 delete
 list
 update
 edit
 watch
 exec
Use case: Create user with limited namespace access
In this example, we will create the following User Account:
 Username: employee
 Group: bitnami
We will add the necessary RBAC policies so this user can fully manage deployments (i.e. use
kubectl run command) only inside the office namespace. At the end, we will test the policies to
make sure they work as expected.
Step 1: Create the office namespace
 Execute the kubectl create command to create the namespace (as the admin user):
kubectl create namespace office
Step 2: Create the user credentials
As previously mentioned, Kubernetes does not have API Objects for User Accounts. Of the
available ways to manage authentication (see Kubernetes official documentation for a complete
list), we will use OpenSSL certificates for their simplicity. The necessary steps are:
 Create a private key for your user. In this example, we will name the file employee.key:
openssl genrsa -out employee.key 2048
 Create a certificate sign request employee.csr using the private key you just created
(employee.key in this example). Make sure you specify your username and group in the -
subj section (CN is for the username and O for the group). As previously mentioned, we
will use employee as the name and bitnami as the group:

66
openssl req -new -key employee.key -out employee.csr -subj
"/CN=employee/O=bitnami"
 Locate your Kubernetes cluster certificate authority (CA). This will be responsible for
approving the request and generating the necessary certificate to access the cluster API.
Its location is normally /etc/kubernetes/pki/. In the case of Minikube, it would be
~/.minikube/. Check that the files ca.crt and ca.key exist in the location.
 Generate the final certificate employee.crt by approving the certificate sign request,
employee.csr, you made earlier. Make sure you substitute the CA_LOCATION placeholder
with the location of your cluster CA. In this example, the certificate will be valid for 500
days:
openssl x509 -req -in employee.csr -CA CA_LOCATION/ca.crt -CAkey
CA_LOCATION/ca.key -CAcreateserial -out employee.crt -days 500
 Save both employee.crt and employee.key in a safe location (in this example we will use
/home/employee/.certs/).
 Add a new context with the new credentials for your Kubernetes cluster. This example is
for a Minikube cluster but it should be similar for others:
kubectl config set-credentials employee --client-
certificate=/home/employee/.certs/employee.crt --client-
key=/home/employee/.certs/employee.key
kubectl config set-context employee-context --cluster=minikube --
namespace=office --user=employee
 Now you should get an access denied error when using the kubectl CLI with this
configuration file. This is expected as we have not defined any permitted operations for
this user.
kubectl --context=employee-context get pods
Step 3: Create the role for managing deployments
 Create a role-deployment-manager.yaml file with the content below. In this yaml file we
are creating the rule that allows a user to execute several operations on Deployments,
Pods and ReplicaSets (necessary for creating a Deployment), which belong to the core
(expressed by "" in the yaml file), apps, and extensions API Groups:
kind: Role
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
namespace: office
name: deployment-manager

67
rules:
- apiGroups: ["", "extensions", "apps"]
resources: ["deployments", "replicasets", "pods"]
verbs: ["get", "list", "watch", "create", "update", "patch", "delete"] # You
can also use ["*"]
 Create the Role in the cluster using the kubectl create role command:
kubectl create -f role-deployment-manager.yaml
Step 4: Bind the role to the employee user
 Create a rolebinding-deployment-manager.yaml file with the content below. In this file,
we are binding the deployment-manager Role to the User Account employee inside the
office namespace:
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
name: deployment-manager-binding
namespace: office
subjects:
- kind: User
name: employee
apiGroup: ""
roleRef:
kind: Role
name: deployment-manager
apiGroup: ""
 Deploy the RoleBinding by running the kubectl create command:
kubectl create -f rolebinding-deployment-manager.yaml
Step 5: Test the RBAC rule
Now you should be able to execute the following commands without any issues:
kubectl --context=employee-context run --image bitnami/dokuwiki
mydokuwiki
kubectl --context=employee-context get pods

68
If you run the same command with the --namespace=default argument, it will fail, as the
employee user does not have access to this namespace.
kubectl --context=employee-context get pods --namespace=default
Now you have created a user with limited permissions in your cluster.
Secrets
 Secret - At the application level, Kubernetes secrets can store sensitive information (such
as passwords, SSH keys, API keys or tokens) per cluster (a virtual cluster if using
namespaces, physical otherwise).
Kubernetes Secret can be injected into a Pod container either as an environment
variable or mounted as a file.
Using Kubernetes Secrets allows us to abstract sensitive data and configuration
from application deployment.
Note that secrets are accessible from any pod in the same cluster. Network
policies for access to pods can be defined in a deployment. A network policy
specifies how pods are allowed to communicate with each other and with other
network endpoints.
Note that storing sensitive data in a Kubernetes Secret does not make it secure.
By default, all data in Kubernetes Secrets is stored as a plaintext encoded with
base64.
There are multiple ways of creating secrets in Kubernetes.
 Creating from txt files.
 Creating from yaml file.
Creating From Text File
In order to create secrets from a text file such as user name and password, we first need to store
them in a txt file and use the following command.
$ kubectl create secret generic tomcat-passwd –-from-file = ./username.txt –
fromfile = ./.password.txt
Creating From Yaml File
apiVersion: v1

69
kind: Secret
metadata:
name: tomcat-pass
type: Opaque
data:
password: <User Password>
username: <User Name>
Creating the Secret
$ kubectl create –f Secret.yaml secrets/tomcat-pass
Using Secrets
Once we have created the secrets, it can be consumed in a pod or the replication controller as −
 Environment Variable
 Volume
As Environment Variable
In order to use the secret as environment variable, we will use env under the spec section of pod
yaml file.
env:
- name: SECRET_USERNAME
valueFrom:
secretKeyRef:
name: mysecret
key: tomcat-pass
As Volume
spec:
volumes:
- name: "secretstest"
secret:
secretName: tomcat-pass
containers:
- image: tomcat:7.0
name: awebserver
volumeMounts:
- mountPath: "/tmp/mysec"
name: "secretstest"

70
Secret Configuration as Environment Variable
apiVersion: v1
kind: ReplicationController
metadata:
name: appname
spec:
replicas: replica_count
template:
metadata:
name: appname
spec:
nodeSelector:
resource-group:
containers:
- name: appname
image:
imagePullPolicy: Always
ports:
- containerPort: 3000
env: -----------------------------> 1
- name: ENV
valueFrom:
configMapKeyRef:
name: appname
key: tomcat-secrets
In the above code, under the env definition, we are using secrets as environment variable in the
replication controller.
Secrets as Volume Mount
apiVersion: v1
kind: pod
metadata:
name: appname
spec:
metadata:
name: appname
spec:
volumes:
- name: "secretstest"
secret:
secretName: tomcat-pass
containers:
- image: tomcat: 8.0
name: awebserver
volumeMounts:
- mountPath: "/tmp/mysec"
name: "secretstest"

71
Kubernetes Logging & Monitoring
Monitoring is one of the key component for managing large clusters. For this, we have a number
of tools.
Monitoring with Prometheus
It is a monitoring and alerting system. It was built at SoundCloud and was open sourced in 2012.
It handles the multi-dimensional data very well.
Sematext Docker Agent
It is a modern Docker-aware metrics, events, and log collection agent. It runs as a tiny container
on every Docker host and collects logs, metrics, and events for all cluster node and containers. It
discovers all containers (one pod might contain multiple containers) including containers for
Kubernetes core services, if the core services are deployed in Docker containers. After its
deployment, all logs and metrics are immediately available out of the box.
Kubernetes Log
Kubernetes containers’ logs are not much different from Docker container logs. However,
Kubernetes users need to view logs for the deployed pods. Hence, it is very useful to have
Kubernetes-specific information available for log search, such as −
 Kubernetes namespace
 Kubernetes pod name
 Kubernetes container name
 Docker image name
 Kubernetes UID

72
Resources
https://kubernetes.io/docs/
https://wiki.aquasec.com/display/containers/Kubernetes+101
https://www.ibm.com/cloud/architecture/content/course/kubernetes-101
https://kubernetesbyexample.com/
https://www.tutorialspoint.com/kubernetes/index.htm
https://unofficial-kubernetes.readthedocs.io/en/latest/
https://www.katacoda.com/courses/kubernetes
https://access.redhat.com/documentation/en-
us/red_hat_enterprise_linux_atomic_host/7/html/getting_started_with_kubernetes/index

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