Set up Docker Swarm Cluster Using Consul

Docker Swarm is native clustering for Docker. It allows you create and access to a pool of Docker hosts using the full suite of Docker tools. Because Docker Swarm serves the standard Docker API, any tool that already communicates with a Docker daemon can use Swarm to transparently scale to multiple hosts.

Docker Swarm has a Manager, a pre-defined Docker Host, and is a single point for all administration. Swarm manager orchestrates and schedules containers on the entire cluster, and can be configured in High Availability. The containers are deployed on Nodes that are additional Docker Hosts.

Swarm talks to a hosted Discovery Service that maintains a list of IPs in your cluster. For development, its easy to use the default discovery service hosted on Docker Hub. Complete instructions for that are available in Install and Create Docker Swarm. This blog will show how to setup Docker Swarm Cluster using Consul.

Lets get started!

Create Consul Discovery Service

1. Create a Machine that will host discovery service:
   

   docker-machine create -d=virtualbox consul-machine
   Running pre-create checks...
   Creating machine...
   Waiting for machine to be running, this may take a few minutes...
   Machine is running, waiting for SSH to be available...
   Detecting operating system of created instance...
   Provisioning created instance...
   Copying certs to the local machine directory...
   Copying certs to the remote machine...
   Setting Docker configuration on the remote daemon...
   To see how to connect Docker to this machine, run: docker-machine env consul-machine

2. Connect to this Machine:
   

   eval $(docker-machine env consul-machine)

3. Run Consul service using the following Compose file:
   

   myconsul:
     image: progrium/consul
     restart: always
     hostname: consul
     ports:
       - 8500:8500
     command: "-server -bootstrap"

   This file is also available at github.com/arun-gupta/docker-images/tree/master/consul. The service is started as:

   docker-compose up -d
   Pulling myconsul (progrium/consul:latest)...
   latest: Pulling from progrium/consul
   3b4d28ce80e4: Pull complete
   e5ab901dcf2d: Pull complete
   30ad296c0ea0: Pull complete
   3dba40dec256: Pull complete
   f2ef4387b95e: Pull complete
   53bc8dcc4791: Pull complete
   75ed0b50ba1d: Pull complete
   17c3a7ed5521: Pull complete
   8aca9e0ecf68: Pull complete
   4d1828359d36: Pull complete
   46ed7df7f742: Pull complete
   b5e8ce623ef8: Pull complete
   049dca6ef253: Pull complete
   bdb608bc4555: Pull complete
   8b3d489cfb73: Pull complete
   c74500bbce24: Pull complete
   9f3e605442f6: Pull complete
   d9125e9e799b: Pull complete
   Digest: sha256:8cc8023462905929df9a79ff67ee435a36848ce7a10f18d6d0faba9306b97274
   Status: Downloaded newer image for progrium/consul:latest
   Creating consul_myconsul_1

   Started container can be verified as:

   docker ps
   CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
   f05d8dd11e7f progrium/consul "/bin/start -server -" 30 seconds ago Up 29 seconds 53/tcp, 53/udp, 8300-8302/tcp, 8400/tcp, 0.0.0.0:8500->8500/tcp, 8301-8302/udp consul_myconsul_1

Create Docker Swarm Cluster Using Consul

Swarm is fully integrated with the machine, and so is the easiest way to get started.

1. Create a Swarm Master using the Consul discovery service:
   

   docker-machine create -d virtualbox --swarm --swarm-master --swarm-discovery="consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-store=consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-advertise=eth1:2376" swarm-master
   Running pre-create checks...
   Creating machine...
   Waiting for machine to be running, this may take a few minutes...
   Machine is running, waiting for SSH to be available...
   Detecting operating system of created instance...
   Provisioning created instance...
   Copying certs to the local machine directory...
   Copying certs to the remote machine...
   Setting Docker configuration on the remote daemon...
   Configuring swarm...
   To see how to connect Docker to this machine, run: docker-machine env swarm-master

   
   Three options here:
   • --swarm-discovery defines address of the discovery service.
   • --cluster-advertise advertises the machine on the network.
   • --cluster-store designates a distributed k/v storage backend for the cluster.
   In addition, --swarm configures the machine with Swarm and --swarm-master configures the created Machine to be Swarm master.
2. Connect to this newly created master and find some information about it:

   eval "$(docker-machine env swarm-master)"
   docker info

   This will show the output as:

   docker info
   Containers: 2
   Images: 8
   Server Version: 1.9.0
   Storage Driver: aufs
    Root Dir: /mnt/sda1/var/lib/docker/aufs
    Backing Filesystem: tmpfs
    Dirs: 12
    Dirperm1 Supported: true
   Execution Driver: native-0.2
   Logging Driver: json-file
   Kernel Version: 4.1.12-boot2docker
   Operating System: Boot2Docker 1.9.0 (TCL 6.4); master : 16e4a2a - Tue Nov  3 19:49:22 UTC 2015
   CPUs: 1
   Total Memory: 996.2 MiB
   Name: swarm-master
   ID: 2EDA:WPOD:YVWO:GGLZ:ZUHY:WCBU:ZERW:OWBE:6MPQ:IPXN:BS2V:QCSI
   Debug mode (server): true
    File Descriptors: 30
    Goroutines: 67
    System Time: 2015-11-29T02:08:10.636829121Z
    EventsListeners: 1
    Init SHA1: 
    Init Path: /usr/local/bin/docker
    Docker Root Dir: /mnt/sda1/var/lib/docker
   Username: arungupta
   Registry: https://index.docker.io/v1/
   Labels:
    provider=virtualbox
   Cluster store: consul://192.168.99.109:8500
   Cluster advertise: 192.168.99.111:2376

3. Create a new machine to be part of this Swarm cluster:

   docker-machine create -d virtualbox --swarm --swarm-discovery="consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-store=consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-advertise=eth1:2376" swarm-node-01
   Running pre-create checks...
   Creating machine...
   Waiting for machine to be running, this may take a few minutes...
   Machine is running, waiting for SSH to be available...
   Detecting operating system of created instance...
   Provisioning created instance...
   Copying certs to the local machine directory...
   Copying certs to the remote machine...
   Setting Docker configuration on the remote daemon...
   Configuring swarm...
   To see how to connect Docker to this machine, run: docker-machine env swarm-node-01

   Machine talks to the Discovery Service using --swarm-discovery.
4. Create a second node in this cluster:

   docker-machine create -d virtualbox --swarm --swarm-discovery="consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-store=consul://$(docker-machine ip consul-machine):8500" --engine-opt="cluster-advertise=eth1:2376" swarm-node-02
   Running pre-create checks...
   Creating machine...
   Waiting for machine to be running, this may take a few minutes...
   Machine is running, waiting for SSH to be available...
   Detecting operating system of created instance...
   Provisioning created instance...
   Copying certs to the local machine directory...
   Copying certs to the remote machine...
   Setting Docker configuration on the remote daemon...
   Configuring swarm...
   To see how to connect Docker to this machine, run: docker-machine env swarm-node-02

5. List all the created machines:

   docker-machine ls 
   NAME             ACTIVE   DRIVER       STATE     URL                         SWARM
   consul-machine   -        virtualbox   Running   tcp://192.168.99.109:2376   
   default          -        virtualbox   Running   tcp://192.168.99.100:2376   
   swarm-master     *        virtualbox   Running   tcp://192.168.99.111:2376   swarm-master (master)
   swarm-node-01    -        virtualbox   Running   tcp://192.168.99.112:2376   swarm-master
   swarm-node-02    -        virtualbox   Running   tcp://192.168.99.113:2376   swarm-master

   The machines that are part of the cluster have cluster’s name in the SWARM column, blank otherwise. For example, “default” and “consul-machine” are standalone machines where as all other machines are part of the “swarm-master” cluster. The Swarm master is also identified by (master) in the SWARM column.
6. Connect to the Swarm cluster and find some information about it:

   eval "$(docker-machine env --swarm swarm-master)"
   docker info

   The main difference here is --swarm when finding information about Swarm cluster as opposed to a single machine.This shows the output as:

   docker info
   Containers: 4
   Images: 3
   Role: primary
   Strategy: spread
   Filters: health, port, dependency, affinity, constraint
   Nodes: 3
    swarm-master: 192.168.99.111:2376
     └ Containers: 2
     └ Reserved CPUs: 0 / 1
     └ Reserved Memory: 0 B / 1.021 GiB
     └ Labels: executiondriver=native-0.2, kernelversion=4.1.12-boot2docker, operatingsystem=Boot2Docker 1.9.0 (TCL 6.4); master : 16e4a2a - Tue Nov  3 19:49:22 UTC 2015, provider=virtualbox, storagedriver=aufs
    swarm-node-01: 192.168.99.112:2376
     └ Containers: 1
     └ Reserved CPUs: 0 / 1
     └ Reserved Memory: 0 B / 1.021 GiB
     └ Labels: executiondriver=native-0.2, kernelversion=4.1.12-boot2docker, operatingsystem=Boot2Docker 1.9.0 (TCL 6.4); master : 16e4a2a - Tue Nov  3 19:49:22 UTC 2015, provider=virtualbox, storagedriver=aufs
    swarm-node-02: 192.168.99.113:2376
     └ Containers: 1
     └ Reserved CPUs: 0 / 1
     └ Reserved Memory: 0 B / 1.021 GiB
     └ Labels: executiondriver=native-0.2, kernelversion=4.1.12-boot2docker, operatingsystem=Boot2Docker 1.9.0 (TCL 6.4); master : 16e4a2a - Tue Nov  3 19:49:22 UTC 2015, provider=virtualbox, storagedriver=aufs
   CPUs: 3
   Total Memory: 3.064 GiB
   Name: 10edc606d097

   There are three nodes – one Swarm master and two Swarm _worker_ nodes. There is a total of four containers running in this cluster – one Swarm agent on master and each node, and there is an additional swarm-agent-master running on the master. This can be verified by connecting to the master and listing all the containers.
7. List nodes in the cluster with the following command:

   docker run swarm list consul://$(docker-machine ip consul-machine):8500
   192.168.99.111:2376
   192.168.99.112:2376
   192.168.99.113:2376