Swarm Manager High Availability (HA)

Swarm managers

Swarm clusters are highly available (HA), meaning one or more managers can fail, and the swarm will keep running.

Technically speaking, Swarm implements active/passive multi-manager HA. This means a swarm with three managers will have one active manager, and the other two will be passive. In a swarm, we call the active manager the leader and the passive manager's followers, and the leader is the only manager that can update the swarm configuration. If the leader fails, one of the followers will be elected as the new leader, and the swarm will keep running without any service interruption. If you send commands to a follower, it proxies them to the leader.

Command execution in a swarm

The figure below shows you issuing a command to a follower manager requesting an update to the swarm.

• Step 1 shows you issuing the command.

• Step 2 shows the follower manager receiving and proxying the command to the leader.

• Step 3 shows the leader executing it.