Join nodes to a swarm
When you first create a swarm, you place a single Docker Engine into swarm mode. To take full advantage of swarm mode you can add nodes to the swarm:
- Adding worker nodes increases capacity. When you deploy a service to a swarm, the Engine schedules tasks on available nodes whether they are worker nodes or manager nodes. When you add workers to your swarm, you increase the scale of the swarm to handle tasks without affecting the manager raft consensus.
- Manager nodes increase fault-tolerance. Manager nodes perform the orchestration and cluster management functions for the swarm. Among manager nodes, a single leader node conducts orchestration tasks. If a leader node goes down, the remaining manager nodes elect a new leader and resume orchestration and maintenance of the swarm state. By default, manager nodes also run tasks.
The Docker Engine joins the swarm depending on the join-token you provide to
docker swarm join command. The node only uses the token at join time. If
you subsequently rotate the token, it doesn't affect existing swarm nodes. Refer
Run Docker Engine in swarm mode.
To retrieve the join command including the join token for worker nodes, run the following command on a manager node:
$ docker swarm join-token worker To add a worker to this swarm, run the following command: docker swarm join \ --token SWMTKN-1-49nj1cmql0jkz5s954yi3oex3nedyz0fb0xx14ie39trti4wxv-8vxv8rssmk743ojnwacrr2e7c \ 192.168.99.100:2377
Run the command from the output on the worker to join the swarm:
$ docker swarm join \ --token SWMTKN-1-49nj1cmql0jkz5s954yi3oex3nedyz0fb0xx14ie39trti4wxv-8vxv8rssmk743ojnwacrr2e7c \ 192.168.99.100:2377 This node joined a swarm as a worker.
docker swarm join command does the following:
- switches the Docker Engine on the current node into swarm mode.
- requests a TLS certificate from the manager.
- names the node with the machine hostname
- joins the current node to the swarm at the manager listen address based upon the swarm token.
- sets the current node to
Activeavailability, meaning it can receive tasks from the scheduler.
- extends the
ingressoverlay network to the current node.
When you run
docker swarm join and pass the manager token, the Docker Engine
switches into swarm mode the same as for workers. Manager nodes also participate
in the raft consensus. The new nodes should be
Reachable, but the existing
manager remains the swarm
Docker recommends three or five manager nodes per cluster to implement high availability. Because swarm mode manager nodes share data using Raft, there must be an odd number of managers. The swarm can continue to function after as long as a quorum of more than half of the manager nodes are available.
For more detail about swarm managers and administering a swarm, see Administer and maintain a swarm of Docker Engines.
To retrieve the join command including the join token for manager nodes, run the following command on a manager node:
$ docker swarm join-token manager To add a manager to this swarm, run the following command: docker swarm join \ --token SWMTKN-1-61ztec5kyafptydic6jfc1i33t37flcl4nuipzcusor96k7kby-5vy9t8u35tuqm7vh67lrz9xp6 \ 192.168.99.100:2377
Run the command from the output on the new manager node to join it to the swarm:
$ docker swarm join \ --token SWMTKN-1-61ztec5kyafptydic6jfc1i33t37flcl4nuipzcusor96k7kby-5vy9t8u35tuqm7vh67lrz9xp6 \ 192.168.99.100:2377 This node joined a swarm as a manager.