High availability in Swarm
High availability in Docker Swarm
In Docker Swarm, the Swarm manager is responsible for the entire cluster and manages the resources of multiple Docker hosts at scale. If the Swarm manager dies, you must create a new one and deal with an interruption of service.
The High Availability feature allows a Docker Swarm to gracefully handle the failover of a manager instance. Using this feature, you can create a single primary manager instance and multiple replica instances.
A primary manager is the main point of contact with the Docker Swarm cluster. You can also create and talk to replica instances that will act as backups. Requests issued on a replica are automatically proxied to the primary manager. If the primary manager fails, a replica takes away the lead. In this way, you always keep a point of contact with the cluster.