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Replicated Sharding improvements (#29483)

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* WIP

* Finishing touches to sharding updates

* Review feedback
This commit is contained in:
Christopher Batey 2020-08-13 11:27:00 +01:00
parent 779e827495
commit 849018b81e
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akka-docs/src/main/paradox/typed/replicated-eventsourcing.md
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@ -298,27 +298,50 @@ When comparing two version vectors `v1` and `v2`:
## Sharded Replicated Event Sourced entities
To simplify what probably are the most common use cases for how you will want to distribute the replicated actors there is a minimal API for running multiple instances of @ref[Akka Cluster Sharding](cluster-sharding.md),
each instance holding the entities for a single replica.
There are three ways to integrate replicated event sourced entities with sharding:
The distribution of the replicas can be controlled either through cluster roles or using the @ref[multi datacenter](cluster-dc.md) support in Akka Cluster.
* Ensure that each replica has a unique entity id by using the replica id as part of the entity id
* Use @ref[multi datacenter](cluster-dc.md) to run a full copy of sharding per replica
* Use roles to run a full copy of sharding per replica
The API consists of bootstrapping logic for starting the sharding instances through @apidoc[ReplicatedShardingExtension] available from the
To simplify all three cases the @apidoc[ReplicatedShardingExtension] is available from the
`akka-cluster-sharding-typed` module.
Scala
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/ReplicatedShardingSpec.scala) { #bootstrap }
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.scala) { #bootstrap }
Java
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/akka/cluster/sharding/typed/ReplicatedShardingTest.java) { #bootstrap }
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.java) { #bootstrap }
This will run a single instance of sharding and the replicas will be differentiated by having the replica id in the sharding entity id.
Replicas could be on the same node if they end up in the same shard or if the shards get allocated to the same node.
To prevent this roles can be used. You could for instance add a cluster role per availability zone / rack and have a replica per rack.
Scala
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.scala) { #bootstrap-role }
Java
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.java) { #bootstrap-role }
Lastly if your Akka Cluster is setup across DCs you can run a replica per DC.
Scala
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.scala) { #bootstrap-dc }
Java
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.java) { #bootstrap-dc }
Regardless of which replication strategy you use sending messages to the replicated entities is the same.
`init` returns an @apidoc[ReplicatedSharding] instance which gives access to @apidoc[EntityRef]s for each of the replicas for arbitrary routing logic:
Scala
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/akka/cluster/sharding/typed/ReplicatedShardingSpec.scala) { #all-entity-refs }
: @@snip [ReplicatedShardingSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.scala) { #sending-messages }
Java
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/akka/cluster/sharding/typed/ReplicatedShardingTest.java) { #all-entity-refs }
: @@snip [ReplicatedShardingTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/ReplicatedShardingCompileOnlySpec.java) { #sending-messages }
More advanced routing among the replicas is currently left as an exercise for the reader (or may be covered in a future release [#29281](https://github.com/akka/akka/issues/29281), [#29319](https://github.com/akka/akka/issues/29319)).