Building a Docker Swarm cluster

Docker introduced swarm mode to its Docker engine from version 1.12.0. Docker Swarm allows us to pool together multiple Docker hosts to deploy our containers in a scalable and high availability way. In this section, we will build a small Docker Swarm cluster.

Let's dive into building our cluster with the following steps:

1. First, we will go to our Docker host and initialize it as a manager. manager is responsible for maintaining the state of our Docker Swarm cluster. It also dispatches tasks to other Docker hosts in our cluster. Let's type the following command to begin the initialization:

dockerhost$ docker swarm init
Swarm initialized: current node (w49smc2ciy100gaecgx77yir3) 
is now a manager

To add a worker to this swarm, run the following command:

docker swarm join --token SWMTKN-1-4wbs...aq2r \
172.16.132.187:2377

The preceding command generated a token that will be used by other Docker hosts to join our cluster.

1. Next, we will go to a new Docker host called node1. We use the token from the previous step to make this Docker host join our Docker Swarm cluster as a worker. Workers are members of the cluster that are responsible for running our containers. Let's now type the following command to make this new node join our cluster:

node1$ docker swarm join --token SWMTKN-1-4...aq2r \ 172.16.132.187:2377
This node joined a swarm as a worker.

We have now finished setting up our Docker Swarm cluster. Let's go back to our Docker client workstation and confirm the members of our cluster:

client$ docker node ls
ID       HOSTNAME   STATUS  AVAILABILITY MANAGER STATUS ENGINE VERSION
w49smc * dockerhost Ready   Active       Leader         18.09.0
2e0aif   node1      Ready   Active                      18.09.0