The initial contact paths should be assumed as published as that's what client subscribers will receive upon subscription. Any changes to contact points are a delta to that.
* CoordinatedShutdown that can run tasks for configured phases in order (DAG)
* coordinate handover/shutdown of singleton with cluster exiting/shutdown
* phase config obj with depends-on list
* integrate graceful leaving of sharding in coordinated shutdown
* add timeout and recover
* add some missing artery ports to tests
* leave via CoordinatedShutdown.run
* optionally exit-jvm in last phase
* run via jvm shutdown hook
* send ExitingConfirmed to leader before shutdown of Exiting
to not have to wait for failure detector to mark it as
unreachable before removing
* the unreachable signal is still kept as a safe guard if
message is lost or leader dies
* PhaseClusterExiting vs MemberExited in ClusterSingletonManager
* terminate ActorSystem when cluster shutdown (via Down)
* add more predefined and custom phases
* reference documentation
* migration guide
* problem when the leader order was sys2, sys1, sys3,
then sys3 could not perform it's duties and move Leving sys1 to
Exiting because it was observing sys1 as unreachable
* exclude Leaving with exitingConfirmed from convergence condidtion
* Provide shorter aliases for the ActorRefProviders #20649
* Use the new actorefprovider aliases throughout code and docs
* Cleaner alias replacement logic
Allows the cluster client and its receptionist to be observable in terms of contact points becoming available and client heartbeats. Furthermore a query API for requesting the current state has been provided.
* number-of-contacts is by default 3, and in this test
with 4 server nodes we shutdown all but one in the end
and sometimes the client has all other except the remaining
node in its list of contacts, so it will never get contact
with the remaining node
* because it will result in quarantine if failure
detection triggers and that kind of coupling is
exactly what is not desired for a ClusterClient
* replace by simple heartbeat failure detection,
DeadlineFailureDetector
* DeadLetterSuppression
