You have already seen the join command used in the preceding docker swarm join-token section. The join command is used, in conjunction with a cryptographic join token, to add a Docker node to the swarm. All nodes except the very first node will use the join command to become part of the swarm (the first node uses the "init" command, of course). The join command has a few parameters, the most important of them being the --token parameter. This is the required join token, obtainable with the join-token command. Here is an example:

# Join this node to an existing swarm
docker swarm join --token SWMTKN-1-3ovu7fbnqfqlw66csvvfw5xgljl26mdv0dudcdssjdcltk2sen-a830tv7e8bajxu1k5dc0045zn 192.168.159.156:2377

You will notice that the role is not needed for this command. This is because the token itself is associated with the role it has been created for. When you execute the join, the output provides an informational message telling you what role the node has joined as manager or worker. If you have inadvertently use a manager token to join a worker or vice versa, you can use the leave command to remove a node from the swarm, and then using the token for the actual desired role, rejoin the node to the swarm.