Docker Swarm Introduction

Docker Swarm Introduction

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  Docker Swarm Author :Rajdeep Dua, VMware Twitter : @rajdeepdua Last Updated : March 25 2015
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  Overview • Allows tomanage Docker Cluster Remotely • Key Components – Swarm Manager – Swarm Node – Scheduler – Discovery
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  Architecture Diagram
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  Swarm Manager • Managesthe Nodes in the Cluster • Uses Docker APIs to access the Docker Daemon running on each node • Nodes are added to the Swarm manager by callback from Discovery Service’s fetch() function • Elements of a Swarm Cluster Manager – Event Handler – Map of Nodes – Store – Options
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  Swarm Node • RuntimeInstance representing a node in the Cluster. • Talks to the actual Host using Docker Go Client • Created from a DiscoveryEntry fetched from a Discovery Service • Elements of Swarm Node – Id – IP Address (of remote host) – Map of Containers – Map of Images – Health state of the node – Total CPUs – Used CPUs – Total Memory – Used Memory
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  Scheduler • Responsible forscheduling a container on a Node • Pluggable architecture – Bring your own scheduler • Elements of a Scheduler – Placement Strategy Instance – Array of Filters
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  Scheduler .. contd •The `Docker Swarm` scheduler comes with multiple strategies. • These strategies are used to rank nodes using a scores computed by the strategy. `Docker Swarm` currently supports 2 strategies: – BinPacking Strategy – Random Strategy Usage : You can choose the strategy you want to use with the `-- strategy` flag of `swarm manage`
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  Scheduler .. contd BinPackingstrategy • The BinPacking strategy will rank the nodes using their CPU and RAM available and will return the node the most packed already. • This avoid fragmentation, it will leave room for bigger containers on unused machines. Random strategy • The Random strategy, as it's name says, chooses a random node, it's used mainly for debug
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  Scheduler Filters • Scheduleruses the following filters for container placement on a node – Affinity Filter – Constraint Filter : When creating a container, the user can select a subset of nodes that should be considered for scheduling by specifying one or more sets of matching key/value pairs. – Port Filter : Select node where public port required by the container is not already used – Health Filter : Select only healthy nodes from the cluster
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  Swarm Store • Storesthe state of the Cluster. • Currently implemented as a JSON file • State is loaded in memory when the cluster starts • Lifecycle events of the store – Get state for a key – Store the state of a container – Load all the data stored – Replace the state of the key with a new state – Delete the state
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  Discovery Service • HelpsSwarm Manager discover nodes • Three main functions – Register : Registers a new node – Watch : Callback method for Swarm Manager when a new Node is added to the Discovery Service – Fetch : Fetch the List of Entries
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  Discovery Services • TokenBased • etcd based • Zookeeper based • File Based • Consul Based • Bring your own?
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  Docker Swarm Architecture- Exploded
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  Token Based DiscoveryService • Based on REST End Point hosted on Docker- hub • URL Queried for entries is DISCOVERY_URL = "https://discovery-stage.hub.docker.com/v1" HTTP GET https://discovery-stage.hub.docker.com/v1/clusters/<token-id>
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  Discovery Fetch Entries
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  Swarm CLI • AllowsSetting up and Managing the Cluster create a cluster $ docker run --rm swarm create 6856663cdefdec325839a4b7e1de38e8 On each nodes, start the swarm agent $ docker run -d swarm join --addr=<node_ip:2375> token://<cluster_id>
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  Swarm CLI Start themanager on any machine / Laptop to manage the cluster $ docker run -d -p <swarm_port>:2375 swarm manage token://<cluster_id> Use the regular docker cli $ docker -H tcp://<swarm_ip:swarm_port> info $ docker -H tcp://<swarm_ip:swarm_port> run ... $ docker -H tcp://<swarm_ip:swarm_port> ps $ docker -H tcp://<swarm_ip:swarm_port> logs ... … List nodes in your cluster $ docker run --rm swarm list token://<cluster_id> <node_ip:2375>
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  Swarm APIs • Compatiblewith Docker Remote API with some differences • Containers GET /containers/(id) POST /containers/create DELETE /containers/(id) POST /container/(id)/start additional parameters passed in the POST body
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  Swarm APIs… Images GET /images/json POST/images/create DELETE /images/(id) GET /images/search
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  Summary • Docker Swarmallows you to use native Docker CLI commands and APIs to manage containers across a cluster of nodes • It has a basic scheduler which can be enhanced • Pluggable Discovery mechanism