Providing high availability with Docker Swarm

The Docker Swarm orchestrator will provide out-of-the-box high availability if we use an odd number of manager nodes. The Raft protocol used to manage the internal database requires an odd number of nodes to maintain it healthily. Having said that, the minimum number of healthy managers for the cluster to be fully functional is N/2+1, as discussed earlier in this chapter. However, no matter how many managers are working, your application’s functionality may not be impacted. Worker nodes will continue working even when you don’t have the minimum number of required manager nodes. An application’s services will continue running unless a container fails. In this situation, if the managers aren’t functional, your containers will not be managed by the cluster and thus your application will be impacted. It is important to understand this because it is the key to preparing your clusters for these situations.

Although...