Using Puppet to launch a Docker Swarm

Docker Swarm is part of the official Docker orchestration effort, and allows for managing containers across a fleet of hosts rather than just on a single host.

The Puppet Docker module supports installing and managing Docker, and running individual docker containers. Given Swarm is packaged as containers, that means we can install a Swarm cluster using Puppet.

Swarm supports a number of discovery backends. For this example I'll be using Consul, again all managed by Puppet.

Usage

vagrant up --provider virtualbox

This will launch 2 virtual machines, install Consul and register a cluster, install Docker and Swarm and then establish the swarm.

You can access the swwarm using a docker client, either from you local machine or from one of the virtual machines. For instance:

docker -H tcp://10.20.3.11:3000 info

If you don't have docker installed locally you can run the above command from one of the virtual machines using:

vagrant ssh swarm-1 -c "docker -H tcp://localhost:3000 info"

This should print something like:

Containers: 4
Nodes: 2
 swarm-1: 10.20.3.11:2375
  └ Containers: 3
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB
 swarm-2: 10.20.3.12:2375
  └ Containers: 1
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB

Growing the cluster

We can also automatically scale the cluster by launching additional virtual machines.

INSTANCES=4 vagrant up --provider virtualbox

This will give us a total of 4 virtual machines, 2 new ones and the 2 existing machines we already launched. Once the machines have launched you should be able to run the above commands again, this time you'll get something like:

Containers: 6
Nodes: 4
 swarm-1: 10.20.3.11:2375
  └ Containers: 3
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB
 swarm-2: 10.20.3.12:2375
  └ Containers: 1
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB
 swarm-3: 10.20.3.13:2375
  └ Containers: 1
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB
 swarm-4: 10.20.3.14:2375
  └ Containers: 1
  └ Reserved CPUs: 0 / 1
  └ Reserved Memory: 0 B / 490 MiB

Implementation details

The example uses the Docker module to launch the swarm containers. First we run the main swarm container on all hosts.

::docker::run { 'swarm':
  image   => 'swarm',
  command => "join --addr=${::ipaddress_eth1}:2375 consul://${::ipaddress_eth1}:8500/swarm_nodes"
}

Then on one host we run the swarm manager:

::docker::run { 'swarm-manager':
  image   => 'swarm',
  ports   => '3000:2375',
  command => "manage consul://${::ipaddress_eth1}:8500/swarm_nodes",
  require => Docker::Run['swarm'],
}

Consul is managed by the excellent Consul module from Kyle Anderson. Much of the Consul configuration is in the hiera data, for example:

consul::config_hash:
  data_dir: '/opt/consul'
  client_addr: '0.0.0.0'
  bind_addr: "%{::ipaddress_eth1}"