CKA_1st.pptx

Introduction
Core Concepts
Joseph
2022/4/9

Agenda
• k8s有哪些東西
• Pod
• Replica set
• Deployment
• Service
• Cluster architecture
• High level 視角
• 以容器的形式自動地維持服務
• 部署多個服務

k8s high level
• 架構
• 比喻貨櫃公司＆船隻運貨
• (ship=worker node) 放了一些容器貨櫃
• Master 管理：船隻監控與追蹤
• Key-value store : etcd cluster
• Scheduler
• 排程、分派
• Node-controller
• 監視node健康度（不可用、壞了）
• Replication –controller
• 是否滿足定義的數量
• Api-server
• 對外暴露
• 定時要Kubelet回報狀態
• Kubelet 船長 (每個node)
• 確保載正確的容器、回報狀態給master
• 聽api-server的指令，加載卸載容器
• Kube-proxy
• 確保跨船通信

k8s與docker的關聯
• Docker
• 用來跑容器
• 裝在所有node
• 替代方案：ContainerD, Rocket

ETCDCTL Utility
• 版本：2, 3 是獨立分開的（不互相支援）、預設是2
• ETCDCTL is the CLI tool used to interact with ETCD.
ETCDCTL can interact with ETCD Server using 2 API versions - Version 2 and Version 3. By default its set to use Version 2. Each
version has different sets of commands.
• For example ETCDCTL version 2 supports the following commands:
• etcdctl backup
• etcdctl cluster-health
• etcdctl mk
• etcdctl mkdir
• etcdctl set
• Whereas the commands are different in version 3
• etcdctl snapshot save
• etcdctl endpoint health
• etcdctl get
• etcdctl put
• To set the right version of API set the environment variable ETCDCTL_API command
• export ETCDCTL_API=3

ETCD Cont.
• When API version is not set, it is assumed to be set to version 2. And version 3 commands listed above don't
work. When API version is set to version 3, version 2 commands listed above don't work.
•
• Apart from that, you must also specify path to certificate files so that ETCDCTL can authenticate to the
ETCD API Server. The certificate files are available in the etcd-master at the following path. We discuss more
about certificates in the security section of this course. So don't worry if this looks complex:
• --cacert /etc/kubernetes/pki/etcd/ca.crt
• --cert /etc/kubernetes/pki/etcd/server.crt
• --key /etc/kubernetes/pki/etcd/server.key
•
• specify the ETCDCTL API version and path to certificate files. Below is the final form:
• kubectl exec etcd-master -n kube-system -- sh -c "ETCDCTL_API=3 etcdctl get / --prefix --keys-only --limit=10 --cacert
/etc/kubernetes/pki/etcd/ca.crt --cert /etc/kubernetes/pki/etcd/server.crt --key /etc/kubernetes/pki/etcd/server.key"

Kubectl
• Kubectl cmd  API Server ETCD

Controller manager
• Monitor status
• 有各式各樣的Controller

Kube-scheduler
• 決定讓pod去最適當的node

Kubelet
• 船長
• 要求docker下載image並執行

Kube-proxy
• Deployed as daemon set

• Pod相當於application(Udemy主講說，但。。)
• 一個pod可以有多個container
• Share resources
• 可以網路直連
• 高可用(LB)的創建方式

創建pod
• Create a pod
• YAML主結構

Pratice (在後半段)
• accessing the labs

ReplicaSets
• Replica Sets 可以說是進化版的Replication
Controller，與Replication Controller最大的差異在
於，Replica Sets 提供了更彈性的selector 。

Deployment
• 自動產生
• replicaSet, pod

Certification Tip!
• Create an NGINX Pod
• kubectl run nginx --image=nginx
• Generate POD Manifest YAML file (-o yaml). Don't create it(--dry-run)
• kubectl run nginx --image=nginx --dry-run=client -o yaml
• Create a deployment
• kubectl create deployment --image=nginx nginx
• Generate Deployment YAML file (-o yaml). Don't create it(--dry-run)
• kubectl create deployment --image=nginx nginx --dry-run=client -o yaml
• Generate Deployment YAML file (-o yaml). Don't create it(--dry-run) with 4 Replicas (--replicas=4)
• kubectl create deployment --image=nginx nginx --dry-run=client -o yaml > nginx-deployment.yaml
• Save it to a file, make necessary changes to the file (for example, adding more replicas) and then create the deployment.
• kubectl create -f nginx-deployment.yaml
• OR
• In k8s version 1.19+, we can specify the --replicas option to create a deployment with 4 replicas.
• kubectl create deployment --image=nginx nginx --replicas=4 --dry-run=client -o yaml > nginx-deployment.yaml

Pod 實操
• https://kodekloud.com/topic/practice-test-pods-2/
• controlplane ~ ➜ kubectl run nginx --image=nginx
• pod/nginx created
• controlplane ~ ➜ kubectl describe pod newpods-bk6fb
• controlplane ~ ➜ kubectl get pods -o=wide

• How many containers are part of the pod webapp?
• =>kubectl get pods -o=wide
• What images are used in the new webapp pod?
• =>kubectl describe pod webapp
• Delete the webapp Pod.
• ==>
• controlplane ~ ➜ kubectl delete pod webapp
• pod "webapp" deleted
• Create a new pod with the name redis and with the image redis123.

• controlplane ~ ➜ kubectl create -f redis.yaml
• pod/redis created
• Now change the image on this pod to redis.
• Once done, the pod should be in a running state.
• controlplane ~ ➜ vi redis.yaml
• controlplane ~ ➜ kubectl apply -f redis.yaml

PRACTICE TEST –
REPLICASETS
kubectl get rs
kubectl describe rs new-replica-set
kubectl describe pod new-replica-set-nd9q4
kubectl delete pod new-replica-set-nd9q4
kubectl apply -f replicaset-definition-1.yaml
kubectl delete rs replicaset-1
kubectl edit rs new-replica-set
kubectl delete pod new-replica-set-t2fg8 new-replica-set-zrjwp new-replica-set-gmlsd new-replica-set-6wwwb
kubectl scale rs new-replica-set --replicas=5

RS ensures that desired number of PODs run

kubectl delete rs replicaset-1

kubectl edit rs new-replica-set

kubectl scale rs new-replica-set --replicas=5

PRACTICE TESTS –
DEPLOYMENTS
kubectl get deployments
kubectl apply -f deployment-definition-1.yaml
kubectl create deployment httpd-frontend --image=httpd:2.4-alpine
kubectl scale deployment httpd-frontend --replicas=3

kubectl create deployment httpd-frontend --
image=httpd:2.4-alpine

PRACTICE TEST NAMESPACES
kubectl get ns
kubectl get pod -n research
kubectl describe pod -n research
kubectl run redis --image=redis --dry-run=client -o yaml > pod.yaml
kubectl get pod --all-namespaces
kubectl get pod --all-namespaces | grep blue

kubectl get ns
kubectl get pod -n research

kubectl describe pod -n research
• Create a POD in the finance namespace.
• Use the spec given below.
• Name: redis
• Image Name: redis
• (X) kubectl run redis --image=redis
• Not in the finance namespace.
• kubectl run redis --image=redis
• --dry-run=client -o yaml > pod.yaml

kubectl get pod --all-namespaces

• 直接使用”db-service”可以直接訪問
• 但如果是要訪問別的namespace的
• Ex: dev底下的db-service
• db-service.dev.svc.cluster.local

PRACTICE TEST SERVICES
kubectl get svc
kubectl describe svc Kubernetes
kubectl get deploy

• Default is clusterIP type
• kubectl describe svc kubernetes
• TargetPort, Labels, Endpoints

Access the web application using
the tab 'simple-webapp-ui' above
the terminal window.
• Create a new service to access the web application using the service-
definition-1.yaml file
•
Name: webapp-service
Type: NodePort
targetPort: 8080
port: 8080
nodePort: 30080
selector: simple-webapp

PRACTICE TEST –
IMPERATIVE COMMANDS
kubectl run nginx-pod --image=nginx:alpine
kubectl run redis --image=redis:alpine --labels=tier=db
kubectl expose pod redis --name=redis-service --port=6379 --target-port=6379
kubectl create deploy webapp --image=kodekloud/webapp-color
kubectl run custom-nginx --image=nginx --port=8080
kubectl create ns dev-ns
kubectl expose pod httpd --name=httpd --target-port=80 --port=80

apply –f XXX.yaml
• kubectl run nginx-pod --image=nginx:alpine
• kubectl run redis --image=redis:alpine --dry-run=client -o yaml >
redis.yaml 然後 labels加上tier:db 或者
• kubectl run redis --image=redis:alpine –labels=tier=db

kubectl expose pod redis --name=redis-
service --port=6379 --target-port=6379

kubectl create deploy webapp --
image=kodekloud/webapp-color
• create deploy不用加--name=

kubectl run custom-nginx --image=nginx --
port=8080

• create deploy不用加--name=
• 不能使用--replics=Ｎ

kubectl expose pod 必須同時有--target-
port=80 --port=80

CKA_1st.pptx

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