Does Rancher require quorum for HA? Article http://rancher.com/5-keys-running-workloads-resiliently-rancher-docker-part-1/ gives me the impression that it does.
Excerpts from the article:
Cluster size, notice how everything is odd? Behind the scenes, Rancher HA sets up a ZooKeeper Quorum to keep locks in sync (More on this in the appendix). ZooKeeper recommends odd numbers because an even number of servers does not provide additional fault tolerance.
Appendix
For any distributed system, there is an explicit way to manage state and changes. Multiple servers need a process to coordinate between updates.
Rancher’s management process works by keeping state and desired state in the database; then emitting events to be handled by processing entities to realize the desired state.
When an event is being processed, there is a lock on it, and it is up to the processing entity to update the state in the database.
In the single server setup, all of the coordination happens in memory on the host. Once you go to a multi server setup, the additional components like ZooKeeper and Redis are needed.