Docker Machine

Adding nodes using the Docker API

  • We don't have to SSH into the other nodes, we can use the Docker API

  • If you are using Play-With-Docker:

    • the nodes expose the Docker API over port 2375/tcp, without authentication

    • we will connect by setting the DOCKER_HOST environment variable

  • Otherwise:

    • the nodes expose the Docker API over port 2376/tcp, with TLS mutual authentication

    • we will use Docker Machine to set the correct environment variables
      (the nodes have been suitably pre-configured to be controlled through node1)

Docker Machine

  • Docker Machine has two primary uses:

    • provisioning cloud instances running the Docker Engine

    • managing local Docker VMs within e.g. VirtualBox

  • Docker Machine is purely optional

  • It makes it easy to create, upgrade, manage... Docker hosts:

    • on your favorite cloud provider

    • locally (e.g. to test clustering, or different versions)

    • across different cloud providers

If you're using Play-With-Docker ...

  • You won't need to use Docker Machine

  • Instead, to "talk" to another node, we'll just set DOCKER_HOST

  • You can skip the exercises telling you to do things with Docker Machine!

Docker Machine basic usage

  • We will learn two commands:

    • docker-machine ls (list existing hosts)

    • docker-machine env (switch to a specific host)

  • List configured hosts:
    docker-machine ls

You should see your 5 nodes.

How did we make our 5 nodes show up there?

For the curious...

  • This was done by our VM provisioning scripts

  • After setting up everything else, node1 adds the 5 nodes to the local Docker Machine configuration (located in $HOME/.docker/machine)

  • Nodes are added using Docker Machine generic driver

    (It skips machine provisioning and jumps straight to the configuration phase)

  • Docker Machine creates TLS certificates and deploys them to the nodes through SSH

Selecting a node with Docker Machine

  • To select a node, use eval $(docker-machine env nodeX)

  • This sets a number of environment variables

  • To unset these variables, use eval $(docker-machine env -u)

  • View the variables used by Docker Machine:
    docker-machine env node3

(This shows which variables would be set by Docker Machine; but it doesn't change them.)

Getting the token

  • First, let's store the join token in a variable

  • This must be done from a manager

  • Make sure we talk to the local node, or node1:

    eval $(docker-machine env -u)
  • Get the join token:

    TOKEN=$(docker swarm join-token -q worker)

Change the node targeted by the Docker CLI

  • We need to set the right environment variables to communicate with node3
  • If you're using Play-With-Docker:

    export DOCKER_HOST=tcp://node3:2375
  • Otherwise, use Docker Machine:

    eval $(docker-machine env node3)

Checking which node we're talking to

  • Let's use the Docker API to ask "who are you?" to the remote node
  • Extract the node name from the output of docker info:
    docker info | grep ^Name

This should tell us that we are talking to node3.

Note: it can be useful to use a custom shell prompt reflecting the DOCKER_HOST variable.

Adding a node through the Docker API

  • We are going to use the same docker swarm join command as before
  • Add node3 to the Swarm:
    docker swarm join --token $TOKEN node1:2377

Going back to the local node

  • We need to revert the environment variable(s) that we had set previously
  • If you're using Play-With-Docker, just clear DOCKER_HOST:

    unset DOCKER_HOST
  • Otherwise, use Docker Machine to reset all the relevant variables:

    eval $(docker-machine env -u)

From that point, we are communicating with node1 again.

Checking the composition of our cluster

  • Now that we're talking to node1 again, we can use management commands
  • Check that the node is here:
    docker node ls

Notes Docker Machine with KVM Libvirt