kuhree.com

Recently

Docker Swarm

4 min read

Docker Swarm

What is a swarm ?

A swarm is the cluster managemnet and orchestrationg features embedded in Docker Engine using swarmkit. Swarmkit is a separate project which implements Docker’s orchestration layer and is used directly within Docker.

A swarm consists of N+ docker hosts running in swarm mode. Of the hosts, there are two roles. A given host can have one or both roles.

  • managers, to manage membership and delegation
  • workers, running swarm services

Docker Swarm attempt to run a service according to it’s optimal state as declared. If a worker goes down, swarm will attempt schedule those tasks on another node. A task is a running container, managed by the swarm.

Once a service’s configuration is modified, the swarm will update the configuration stop tasks that are out of date and create new ones matching the new upgrade.

Creating a swarm / Creating a Manager

A swarm requires:

  • networked host machines, ideally 3+ (1 manager, 2 workers).
  • with docker installed
  • the ip of the manager
  • the following ports between machines:
    • Port 2377 TCP for communication with and between manager nodes
    • Port 7946 TCP/UDP for overlay network node discovery
    • Port 4789 UDP (configurable) for overlay network traffic

To initialize a swarm

  1. SSH into your “manager”
  2. Run docker swarm init --advertise--addr <MANAGER-IP>

This should return something like:

$ docker swarm init --advertise-addr 192.168.99.100
Swarm initialized: current node (dxn1zf6l61qsb1josjja83ngz) is now a manager.
 
To add a worker to this swarm, run the following command:
 
    docker swarm join \
    --token <TOKEN> \
    <MANAGER-IP>:2377
 
To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.
  1. Run docker info to view the current state of the swarm:
$ docker info
 
Containers: 2
Running: 0
Paused: 0
Stopped: 2
  ...snip...
Swarm: active
  NodeID: dxn1zf6l61qsb1josjja83ngz
  Is Manager: true
  Managers: 1
  Nodes: 1
  ...snip...
  1. Run the docker node ls command to view information about nodes:
docker node ls
 
ID                           HOSTNAME  STATUS  AVAILABILITY  MANAGER STATUS
dxn1zf6l61qsb1josjja83ngz *  manager1  Ready   Active        Leader

Joining the swarm / Creating Workers

  1. SSH into your “worker”
  2. Run the command from when you created the manager
docker swarm join \
  --token <TOKEN> \
  <MANAGER-IP>:2377

Or, if you don’t have access to that, you can get it by running the following on the manager node:

$ docker swarm join-token worker
 
To add a worker to this swarm, run the following command:
 
    docker swarm join \
    --token <TOKEN>
    <MANAGER-IP>:2377
  1. Repeat, 1-2 on all worker nodes

You can check the status of the nodes on the manager as they join by running:

$ docker node ls
ID                           HOSTNAME  STATUS  AVAILABILITY  MANAGER STATUS
03g1y59jwfg7cf99w4lt0f662    worker2   Ready   Active
9j68exjopxe7wfl6yuxml7a7j    worker1   Ready   Active
dxn1zf6l61qsb1josjja83ngz *  manager1  Ready   Active        Leader

Deploy a service / Run a container

  1. SSH into your “manager”
  2. Deploy the service

You can use a command like the following:

$ docker service create --replicas 1 --name helloworld alpine ping docker.com
 
9uk4639qpg7npwf3fn2aasksr
  1. Run docker service ls to check the status of the service with
  2. Run docker service inspect --pretty <SERVICE-ID> to get details about the specific service. Replace --pretty for --json when needed.
[manager1]$ docker service inspect --pretty helloworld
 
ID:		9uk4639qpg7npwf3fn2aasksr
Name:		helloworld
Service Mode:	REPLICATED
 Replicas:		1
Placement:
UpdateConfig:
 Parallelism:	1
ContainerSpec:
 Image:		alpine
 Args:	ping docker.com
Resources:
Endpoint Mode:  vip
  1. Run docker service ps <SERVICE-ID> to see which nodes are running the service:
[manager1]$ docker service ps helloworld
 
NAME                                    IMAGE   NODE     DESIRED STATE  CURRENT STATE           ERROR               PORTS
helloworld.1.8p1vev3fq5zm0mi8g0as41w35  alpine  worker2  Running        Running 3 minutes
  1. Scale the service

Delete the service

  1. SSH into your “manager”
  2. Run something like docker service rm helloworld

Deploy a Stack / Compose up

  1. Run docker stack deploy to deploy a compose stack

NOTE

The docker stack deploy command uses the legacy Compose file version 3 format, used by Compose V1. The latest format, defined by the Compose specification isn’t compatible with the docker stack deploy command.

For more information about the evolution of Compose, see History of Compose.

Graph View

Backlinks