container.training/docs/machine.md

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

---

class: self-paced

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)

.exercise[

• List configured hosts:

  docker-machine ls
  

]

You should see your 5 nodes.

---

class: in-person

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

---

Using Docker Machine to communicate with a node

• 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)

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

• 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

.exercise[

• Check that the node is here:

  docker node ls
  

]