How to stop the ENTIRE cluster with sharding (spanning multiple machines - nodes) from one actor?
I know I can stop the actor system on 'this' node context.system.terminate()
I know I can stop the local Sharding Region.
I found .prepareForFullClusterShutdown() but it doesn't actually stop the nodes.
I suppose there is no single command to do that, but there must be some way to do this.
There's no out-of-the-box way to do this that I'm aware of: the overall expectation is that there's an external control plane (e.g. kubernetes) which manages this.
However, one could have an actor on every node of the cluster that listens for membership events and also subscribes to a pubsub topic. This actor would track the current cluster membership and, when told to begin a cluster shutdown, it publishes a (e.g.) ShutdownCluster message to the topic and tracks which nodes leave. After some length of time (since distributed pubsub is at-most-once) if there are nodes besides this one that haven't left, it sends it again. Eventually, after all other nodes in the cluster have left, this actor then shuts down its node. When other nodes see a ShutdownCluster message, they immediately shut themselves down.
Of course, this sort of scheme will probably not play nicely with any form of external orchestration (whether it's a container scheduler like kubernetes, mesos, or nomad; or even something simple like monit which notices that the service isn't running and restarts it).