Wednesday, 13 May 2020

Configuring Docker Swarm Hosts with Join Tokens

To configure a new Docker Swarm, its remarkably easy you run the following command on a new Docker host and the Swarm is created:

docker swarm init

A Swarm is of course a cluster of Docker hosts, so the next step after creating a new Swarm is to join manager and worker nodes to the Swarm. Once you run the docker swarm init command the console will display a join-token, which can be used to join a new host to the Swarm. 

It will look something like this. You will see it prepopulates all the details required to successfully join a new Docker host to this Swarm. 

docker swarm join --token SWMTKN-1-26w39jcflglpun070cl0qxwnbqwobwj68e4i1dxdi1w2n3we80-4vftzhty9xqmhmq13tgapnzyq

Its important to understand that a reliable network connection is required between all Docker hosts in Swarm. You will also notice port 2377 is used by the manager and worker nodes to communicate, so this port must be open between the two servers. It is unlikely you will hit any problems here if they are on the same network segment. 

From the console of an existing Docker manager node its possible to generate a new join-token. When you generate a new join-token you state whether the new host is going to join the cluster as a manager or a worker node.

For example create a new join-token for a manager node by running

docker swarm join-token manager


docker swarm join-token worker