remember entities and changing shardIdExtractor (#22894)

* Test case covering changing shard id extractor with remember-entities

* This should do the trick

* Feedback addressed

* Docs and migration guide mention

* Correct logic to persist that entity has moved off off shard

akka-cluster-sharding/src/main/protobuf/ClusterShardingMessages.proto

@@ -52,3 +52,12 @@ message ShardStats {
     required string shard = 1;
     required int32 entityCount = 2;
 }
+
+message StartEntity {
+    required string entityId = 1;
+}
+
+message StartEntityAck {
+    required string entityId = 1;
+    required string shardId = 2;
+}

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala

@@ -47,7 +47,7 @@ private[akka] object Shard {
   sealed trait ShardCommand
 
   /**
-   * When an remembering entities and the entity stops without issuing a `Passivate`, we
+   * When remembering entities and the entity stops without issuing a `Passivate`, we
    * restart it after a back off using this message.
    */
   final case class RestartEntity(entity: EntityId) extends ShardCommand
@@ -170,6 +170,8 @@ private[akka] class Shard(
     case Terminated(ref)                         ⇒ receiveTerminated(ref)
     case msg: CoordinatorMessage                 ⇒ receiveCoordinatorMessage(msg)
     case msg: ShardCommand                       ⇒ receiveShardCommand(msg)
+    case msg: ShardRegion.StartEntity            ⇒ receiveStartEntity(msg)
+    case msg: ShardRegion.StartEntityAck         ⇒ receiveStartEntityAck(msg)
     case msg: ShardRegionCommand                 ⇒ receiveShardRegionCommand(msg)
     case msg: ShardQuery                         ⇒ receiveShardQuery(msg)
     case msg if extractEntityId.isDefinedAt(msg) ⇒ deliverMessage(msg, sender())
@@ -177,7 +179,27 @@ private[akka] class Shard(
 
   def receiveShardCommand(msg: ShardCommand): Unit = msg match {
     case RestartEntity(id)    ⇒ getEntity(id)
-    case RestartEntities(ids) ⇒ ids foreach getEntity
+    case RestartEntities(ids) ⇒ restartEntities(ids)
+  }
+
+  def receiveStartEntity(start: ShardRegion.StartEntity): Unit = {
+    log.debug("Got a request from [{}] to start entity [{}] in shard [{}]", sender(), start.entityId, shardId)
+    getEntity(start.entityId)
+    sender() ! ShardRegion.StartEntityAck(start.entityId, shardId)
+  }
+
+  def receiveStartEntityAck(ack: ShardRegion.StartEntityAck): Unit = {
+    if (ack.shardId != shardId && state.entities.contains(ack.entityId)) {
+      log.debug("Entity [{}] previously owned by shard [{}] started in shard [{}]", ack.entityId, shardId, ack.shardId)
+      processChange(EntityStopped(ack.entityId)) { _ ⇒
+        state = state.copy(state.entities - ack.entityId)
+        messageBuffers.remove(ack.entityId)
+      }
+    }
+  }
+
+  def restartEntities(ids: Set[EntityId]): Unit = {
+    context.actorOf(RememberEntityStarter.props(typeName, shardId, ids, settings, sender()))
   }
 
   def receiveShardRegionCommand(msg: ShardRegionCommand): Unit = msg match {
@@ -318,6 +340,63 @@ private[akka] class Shard(
   }
 }
 
+private[akka] object RememberEntityStarter {
+  def props(
+    typeName:  String,
+    shardId:   ShardRegion.ShardId,
+    ids:       Set[ShardRegion.EntityId],
+    settings:  ClusterShardingSettings,
+    requestor: ActorRef) =
+    Props(new RememberEntityStarter(typeName, shardId, ids, settings, requestor))
+}
+
+/**
+ * INTERNAL API: Actor responsible for starting entities when rememberEntities is enabled
+ */
+private[akka] class RememberEntityStarter(
+  typeName:  String,
+  shardId:   ShardRegion.ShardId,
+  ids:       Set[ShardRegion.EntityId],
+  settings:  ClusterShardingSettings,
+  requestor: ActorRef
+) extends Actor {
+
+  import context.dispatcher
+  import scala.concurrent.duration._
+
+  case object Tick
+
+  val region = ClusterSharding(context.system).shardRegion(typeName)
+  var waitingForAck = ids
+
+  sendStart(ids)
+
+  val tickTask = {
+    val resendInterval = settings.tuningParameters.retryInterval
+    context.system.scheduler.schedule(resendInterval, resendInterval, self, Tick)
+  }
+
+  def sendStart(ids: Set[ShardRegion.EntityId]): Unit = {
+    ids.foreach(id ⇒ region ! ShardRegion.StartEntity(id))
+  }
+
+  override def receive = {
+    case ack: ShardRegion.StartEntityAck ⇒
+      waitingForAck -= ack.entityId
+      // inform whoever requested the start that it happened
+      requestor ! ack
+      if (waitingForAck.isEmpty) context.stop(self)
+
+    case Tick ⇒
+      sendStart(waitingForAck)
+
+  }
+
+  override def postStop(): Unit = {
+    tickTask.cancel()
+  }
+}
+
 /**
  * INTERNAL API: Common things for PersistentShard and DDataShard
  */

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ShardRegion.scala

@@ -4,6 +4,7 @@
 package akka.cluster.sharding
 
 import java.net.URLEncoder
+
 import akka.pattern.AskTimeoutException
 import akka.util.{ MessageBufferMap, Timeout }
 import akka.pattern.{ ask, pipe }
@@ -12,6 +13,7 @@ import akka.cluster.Cluster
 import akka.cluster.ClusterEvent._
 import akka.cluster.Member
 import akka.cluster.MemberStatus
+
 import scala.collection.immutable
 import scala.concurrent.duration._
 import scala.concurrent.Future
@@ -300,6 +302,19 @@ object ShardRegion {
    */
   private final case class RestartShard(shardId: ShardId)
 
+  /**
+   * When remembering entities and a shard is started, each entity id that needs to
+   * be running will trigger this message being sent through sharding. For this to work
+   * the message *must* be handled by the shard id extractor.
+   */
+  final case class StartEntity(entityId: EntityId) extends ClusterShardingSerializable
+
+  /**
+   * Sent back when a `ShardRegion.StartEntity` message was received and triggered the entity
+   * to start (it does not guarantee the entity successfully started)
+   */
+  final case class StartEntityAck(entityId: EntityId, shardId: ShardRegion.ShardId) extends ClusterShardingSerializable
+
   private def roleOption(role: String): Option[String] =
     if (role == "") None else Option(role)
 
@@ -438,6 +453,7 @@ private[akka] class ShardRegion(
     case cmd: ShardRegionCommand                 ⇒ receiveCommand(cmd)
     case query: ShardRegionQuery                 ⇒ receiveQuery(query)
     case msg: RestartShard                       ⇒ deliverMessage(msg, sender())
+    case msg: StartEntity                        ⇒ deliverStartEntity(msg, sender())
     case msg if extractEntityId.isDefinedAt(msg) ⇒ deliverMessage(msg, sender())
     case unknownMsg                              ⇒ log.warning("Message does not have an extractor defined in shard [{}] so it was ignored: {}", typeName, unknownMsg)
   }
@@ -699,6 +715,15 @@ private[akka] class ShardRegion(
     retryCount = 0
   }
 
+  def deliverStartEntity(msg: StartEntity, snd: ActorRef): Unit = {
+    try {
+      deliverMessage(msg, snd)
+    } catch {
+      case ex: MatchError ⇒
+        log.error(ex, "When using remember-entities the shard id extractor must handle ShardRegion.StartEntity(id).")
+    }
+  }
+
   def deliverMessage(msg: Any, snd: ActorRef): Unit =
     msg match {
       case RestartShard(shardId) ⇒

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/protobuf/ClusterShardingMessageSerializer.scala

@@ -10,7 +10,6 @@ import java.util.zip.GZIPOutputStream
 import scala.annotation.tailrec
 import scala.collection.JavaConverters._
 import scala.collection.breakOut
-
 import akka.actor.ActorRef
 import akka.actor.ExtendedActorSystem
 import akka.cluster.sharding.Shard
@@ -18,11 +17,12 @@ import akka.cluster.sharding.ShardCoordinator
 import akka.cluster.sharding.protobuf.msg.{ ClusterShardingMessages ⇒ sm }
 import akka.serialization.BaseSerializer
 import akka.serialization.Serialization
-import akka.serialization.SerializationExtension
 import akka.serialization.SerializerWithStringManifest
 import akka.protobuf.MessageLite
 import java.io.NotSerializableException
 
+import akka.cluster.sharding.ShardRegion.{ StartEntity, StartEntityAck }
+
 /**
  * INTERNAL API: Protobuf serializer of ClusterSharding messages.
  */
@@ -59,6 +59,9 @@ private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSy
   private val EntityStartedManifest = "CB"
   private val EntityStoppedManifest = "CD"
 
+  private val StartEntityManifest = "EA"
+  private val StartEntityAckManifest = "EB"
+
   private val GetShardStatsManifest = "DA"
   private val ShardStatsManifest = "DB"
 
@@ -89,7 +92,11 @@ private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSy
     GracefulShutdownReqManifest → { bytes ⇒ GracefulShutdownReq(actorRefMessageFromBinary(bytes)) },
 
     GetShardStatsManifest → { bytes ⇒ GetShardStats },
-    ShardStatsManifest → { bytes ⇒ shardStatsFromBinary(bytes) })
+    ShardStatsManifest → { bytes ⇒ shardStatsFromBinary(bytes) },
+
+    StartEntityManifest → { startEntityFromBinary(_) },
+    StartEntityAckManifest → { startEntityAckFromBinary(_) }
+  )
 
   override def manifest(obj: AnyRef): String = obj match {
     case _: EntityState                ⇒ EntityStateManifest
@@ -117,6 +124,9 @@ private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSy
     case _: ShardStopped               ⇒ ShardStoppedManifest
     case _: GracefulShutdownReq        ⇒ GracefulShutdownReqManifest
 
+    case _: StartEntity                ⇒ StartEntityManifest
+    case _: StartEntityAck             ⇒ StartEntityAckManifest
+
     case GetShardStats                 ⇒ GetShardStatsManifest
     case _: ShardStats                 ⇒ ShardStatsManifest
     case _ ⇒
@@ -146,12 +156,15 @@ private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSy
     case GracefulShutdownReq(ref) ⇒
       actorRefMessageToProto(ref).toByteArray
 
-    case m: EntityState   ⇒ entityStateToProto(m).toByteArray
+    case m: EntityState    ⇒ entityStateToProto(m).toByteArray
-    case m: EntityStarted ⇒ entityStartedToProto(m).toByteArray
+    case m: EntityStarted  ⇒ entityStartedToProto(m).toByteArray
-    case m: EntityStopped ⇒ entityStoppedToProto(m).toByteArray
+    case m: EntityStopped  ⇒ entityStoppedToProto(m).toByteArray
 
-    case GetShardStats    ⇒ Array.emptyByteArray
+    case s: StartEntity    ⇒ startEntityToByteArray(s)
-    case m: ShardStats    ⇒ shardStatsToProto(m).toByteArray
+    case s: StartEntityAck ⇒ startEntityAckToByteArray(s)
+
+    case GetShardStats     ⇒ Array.emptyByteArray
+    case m: ShardStats     ⇒ shardStatsToProto(m).toByteArray
 
     case _ ⇒
       throw new IllegalArgumentException(s"Can't serialize object of type ${obj.getClass} in [${getClass.getName}]")
@@ -266,6 +279,29 @@ private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSy
     ShardStats(parsed.getShard, parsed.getEntityCount)
   }
 
+  private def startEntityToByteArray(s: StartEntity): Array[Byte] = {
+    val builder = sm.StartEntity.newBuilder()
+    builder.setEntityId(s.entityId)
+    builder.build().toByteArray
+  }
+
+  private def startEntityFromBinary(bytes: Array[Byte]): StartEntity = {
+    val se = sm.StartEntity.parseFrom(bytes)
+    StartEntity(se.getEntityId)
+  }
+
+  private def startEntityAckToByteArray(s: StartEntityAck): Array[Byte] = {
+    val builder = sm.StartEntityAck.newBuilder()
+    builder.setEntityId(s.entityId)
+    builder.setShardId(s.shardId)
+    builder.build().toByteArray
+  }
+
+  private def startEntityAckFromBinary(bytes: Array[Byte]): StartEntityAck = {
+    val sea = sm.StartEntityAck.parseFrom(bytes)
+    StartEntityAck(sea.getEntityId, sea.getShardId)
+  }
+
   private def resolveActorRef(path: String): ActorRef = {
     system.provider.resolveActorRef(path)
   }

akka-cluster-sharding/src/multi-jvm/scala/akka/cluster/sharding/ClusterShardingRememberEntitiesNewExtractorSpec.scala

@@ -0,0 +1,296 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package akka.cluster.sharding
+
+import java.io.File
+
+import akka.actor._
+import akka.cluster.{ Cluster, MemberStatus }
+import akka.persistence.Persistence
+import akka.persistence.journal.leveldb.{ SharedLeveldbJournal, SharedLeveldbStore }
+import akka.remote.testconductor.RoleName
+import akka.remote.testkit.{ MultiNodeConfig, MultiNodeSpec, STMultiNodeSpec }
+import akka.testkit._
+import com.typesafe.config.ConfigFactory
+import org.apache.commons.io.FileUtils
+
+import scala.concurrent.duration._
+
+object ClusterShardingRememberEntitiesNewExtractorSpec {
+
+  final case class Started(ref: ActorRef)
+
+  def props(probe: Option[ActorRef]): Props = Props(new TestEntity(probe))
+
+  class TestEntity(probe: Option[ActorRef]) extends Actor with ActorLogging {
+    log.info("Entity started: " + self.path)
+    probe.foreach(_ ! Started(self))
+
+    def receive = {
+      case m ⇒ sender() ! m
+    }
+  }
+
+  val shardCount = 5
+
+  val extractEntityId: ShardRegion.ExtractEntityId = {
+    case id: Int ⇒ (id.toString, id)
+  }
+
+  val extractShardId1: ShardRegion.ExtractShardId = {
+    case id: Int                     ⇒ (id % shardCount).toString
+    case ShardRegion.StartEntity(id) ⇒ extractShardId1(id.toInt)
+  }
+
+  val extractShardId2: ShardRegion.ExtractShardId = {
+    // always bump it one shard id
+    case id: Int                     ⇒ ((id + 1) % shardCount).toString
+    case ShardRegion.StartEntity(id) ⇒ extractShardId2(id.toInt)
+  }
+
+}
+
+abstract class ClusterShardingRememberEntitiesNewExtractorSpecConfig(val mode: String) extends MultiNodeConfig {
+  val first = role("first")
+  val second = role("second")
+  val third = role("third")
+  val fourth = role("fourth")
+  val fifth = role("fifth")
+
+  commonConfig(ConfigFactory.parseString(s"""
+    akka.loglevel = DEBUG
+    akka.actor.provider = "cluster"
+    akka.cluster.auto-down-unreachable-after = 0s
+    akka.remote.log-remote-lifecycle-events = off
+    akka.persistence.journal.plugin = "akka.persistence.journal.leveldb-shared"
+    akka.persistence.journal.leveldb-shared {
+      timeout = 5s
+      store {
+        native = off
+        dir = "target/ShardingRememberEntitiesNewExtractorSpec/journal"
+      }
+    }
+    akka.persistence.snapshot-store.plugin = "akka.persistence.snapshot-store.local"
+    akka.persistence.snapshot-store.local.dir = "target/ShardingRememberEntitiesNewExtractorSpec/snapshots"
+    akka.cluster.sharding.state-store-mode = "$mode"
+    akka.cluster.sharding.distributed-data.durable.lmdb {
+      dir = target/ShardingRememberEntitiesNewExtractorSpec/sharding-ddata
+      map-size = 10 MiB
+    }
+    """))
+
+  val roleConfig = ConfigFactory.parseString(
+    """
+      akka.cluster.roles = [sharding]
+    """)
+
+  // we pretend node 4 and 5 are new incarnations of node 2 and 3 as they never run in parallel
+  // so we can use the same lmdb store for them and have node 4 pick up the persisted data of node 2
+  val ddataNodeAConfig = ConfigFactory.parseString(
+    """
+      akka.cluster.sharding.distributed-data.durable.lmdb {
+        dir = target/ShardingRememberEntitiesNewExtractorSpec/sharding-node-a
+      }
+    """)
+  val ddataNodeBConfig = ConfigFactory.parseString(
+    """
+      akka.cluster.sharding.distributed-data.durable.lmdb {
+        dir = target/ShardingRememberEntitiesNewExtractorSpec/sharding-node-b
+      }
+    """)
+
+  nodeConfig(second)(roleConfig.withFallback(ddataNodeAConfig))
+  nodeConfig(third)(roleConfig.withFallback(ddataNodeBConfig))
+  nodeConfig(fourth)(roleConfig.withFallback(ddataNodeAConfig))
+  nodeConfig(fifth)(roleConfig.withFallback(ddataNodeBConfig))
+
+}
+
+object PersistentClusterShardingRememberEntitiesSpecNewExtractorConfig extends ClusterShardingRememberEntitiesNewExtractorSpecConfig(
+  ClusterShardingSettings.StateStoreModePersistence)
+object DDataClusterShardingRememberEntitiesNewExtractorSpecConfig extends ClusterShardingRememberEntitiesNewExtractorSpecConfig(
+  ClusterShardingSettings.StateStoreModeDData)
+
+class PersistentClusterShardingRememberEntitiesNewExtractorSpec extends ClusterShardingRememberEntitiesNewExtractorSpec(
+  PersistentClusterShardingRememberEntitiesSpecNewExtractorConfig)
+
+class PersistentClusterShardingRememberEntitiesNewExtractorMultiJvmNode1 extends PersistentClusterShardingRememberEntitiesNewExtractorSpec
+class PersistentClusterShardingRememberEntitiesNewExtractorMultiJvmNode2 extends PersistentClusterShardingRememberEntitiesNewExtractorSpec
+class PersistentClusterShardingRememberEntitiesNewExtractorMultiJvmNode3 extends PersistentClusterShardingRememberEntitiesNewExtractorSpec
+class PersistentClusterShardingRememberEntitiesNewExtractorMultiJvmNode4 extends PersistentClusterShardingRememberEntitiesNewExtractorSpec
+class PersistentClusterShardingRememberEntitiesNewExtractorMultiJvmNode5 extends PersistentClusterShardingRememberEntitiesNewExtractorSpec
+
+class DDataClusterShardingRememberEntitiesNewExtractorSpec extends ClusterShardingRememberEntitiesNewExtractorSpec(
+  DDataClusterShardingRememberEntitiesNewExtractorSpecConfig)
+
+class DDataClusterShardingRememberEntitiesNewExtractorMultiJvmNode1 extends DDataClusterShardingRememberEntitiesNewExtractorSpec
+class DDataClusterShardingRememberEntitiesNewExtractorMultiJvmNode2 extends DDataClusterShardingRememberEntitiesNewExtractorSpec
+class DDataClusterShardingRememberEntitiesNewExtractorMultiJvmNode3 extends DDataClusterShardingRememberEntitiesNewExtractorSpec
+class DDataClusterShardingRememberEntitiesNewExtractorMultiJvmNode4 extends DDataClusterShardingRememberEntitiesNewExtractorSpec
+class DDataClusterShardingRememberEntitiesNewExtractorMultiJvmNode5 extends DDataClusterShardingRememberEntitiesNewExtractorSpec
+
+abstract class ClusterShardingRememberEntitiesNewExtractorSpec(config: ClusterShardingRememberEntitiesNewExtractorSpecConfig) extends MultiNodeSpec(config) with STMultiNodeSpec with ImplicitSender {
+  import ClusterShardingRememberEntitiesNewExtractorSpec._
+  import config._
+
+  val typeName = "Entity"
+
+  override def initialParticipants = roles.size
+
+  val storageLocations = List(new File(system.settings.config.getString(
+    "akka.cluster.sharding.distributed-data.durable.lmdb.dir")).getParentFile)
+
+  override protected def atStartup() {
+    storageLocations.foreach(dir ⇒ if (dir.exists) FileUtils.deleteQuietly(dir))
+    enterBarrier("startup")
+  }
+
+  override protected def afterTermination() {
+    storageLocations.foreach(dir ⇒ if (dir.exists) FileUtils.deleteQuietly(dir))
+  }
+
+  def join(from: RoleName, to: RoleName): Unit = {
+    runOn(from) {
+      Cluster(system) join node(to).address
+    }
+    enterBarrier(from.name + "-joined")
+  }
+
+  val cluster = Cluster(system)
+
+  def startShardingWithExtractor1(): Unit = {
+    ClusterSharding(system).start(
+      typeName = typeName,
+      entityProps = ClusterShardingRememberEntitiesNewExtractorSpec.props(None),
+      settings = ClusterShardingSettings(system).withRememberEntities(true).withRole("sharding"),
+      extractEntityId = extractEntityId,
+      extractShardId = extractShardId1)
+  }
+
+  def startShardingWithExtractor2(): Unit = {
+    ClusterSharding(system).start(
+      typeName = typeName,
+      entityProps = ClusterShardingRememberEntitiesNewExtractorSpec.props(Some(testActor)),
+      settings = ClusterShardingSettings(system).withRememberEntities(true).withRole("sharding"),
+      extractEntityId = extractEntityId,
+      extractShardId = extractShardId2)
+  }
+
+  lazy val region = ClusterSharding(system).shardRegion(typeName)
+
+  def isDdataMode: Boolean = mode == ClusterShardingSettings.StateStoreModeDData
+
+  s"Cluster with min-nr-of-members using sharding ($mode)" must {
+
+    if (!isDdataMode) {
+      "setup shared journal" in {
+        // start the Persistence extension
+        Persistence(system)
+        runOn(first) {
+          system.actorOf(Props[SharedLeveldbStore], "store")
+        }
+        enterBarrier("persistence-started")
+
+        runOn(second, third, fourth, fifth) {
+          system.actorSelection(node(first) / "user" / "store") ! Identify(None)
+          val sharedStore = expectMsgType[ActorIdentity](10.seconds).ref.get
+          SharedLeveldbJournal.setStore(sharedStore, system)
+        }
+
+        enterBarrier("after-1")
+      }
+    }
+
+    "start up first cluster and sharding" in within(15.seconds) {
+      join(first, first)
+      join(second, first)
+      join(third, first)
+
+      runOn(first, second, third) {
+        within(remaining) {
+          awaitAssert {
+            cluster.state.members.count(_.status == MemberStatus.Up) should ===(3)
+          }
+        }
+      }
+      runOn(second, third) {
+        startShardingWithExtractor1()
+      }
+      enterBarrier("first-cluster-up")
+
+      runOn(second, third) {
+        // one entity for each shard id
+        (1 to 10).foreach { n ⇒
+          region ! n
+          expectMsg(n)
+        }
+      }
+      enterBarrier("first-cluster-entities-up")
+    }
+
+    "shutdown sharding nodes" in within(30.seconds) {
+      runOn(first) {
+        testConductor.exit(second, 0).await
+        testConductor.exit(third, 0).await
+      }
+      runOn(first) {
+        within(remaining) {
+          awaitAssert {
+            cluster.state.members.count(_.status == MemberStatus.Up) should ===(1)
+          }
+        }
+      }
+      enterBarrier("first-sharding-cluster-stopped")
+    }
+
+    "start new nodes with different extractor" in within(15.seconds) {
+
+      // start it with a new shard id extractor, which will put the entities
+      // on different shards
+
+      join(fourth, first)
+      join(fifth, first)
+      runOn(first) {
+        within(remaining) {
+          awaitAssert {
+            cluster.state.members.count(_.status == MemberStatus.Up) should ===(3)
+          }
+        }
+      }
+      runOn(fourth, fifth) {
+        startShardingWithExtractor2()
+      }
+
+      // TODO how do we know that the shards has started??
+      Thread.sleep(7000)
+      enterBarrier("new-nodes-started")
+    }
+
+    "have the remembered entities running on the right shards" in within(15.seconds) {
+      runOn(fourth, fifth) {
+        var stats: ShardRegion.CurrentShardRegionState = null
+        within(remaining) {
+          awaitAssert {
+            region ! ShardRegion.GetShardRegionState
+            val reply = expectMsgType[ShardRegion.CurrentShardRegionState]
+            reply.shards should not be empty
+            stats = reply
+          }
+        }
+
+        for {
+          shardState ← stats.shards
+          entityId ← shardState.entityIds
+        } {
+          val calculatedShardId = extractShardId2(entityId.toInt)
+          calculatedShardId should ===(shardState.shardId)
+        }
+      }
+
+      enterBarrier("done")
+    }
+
+  }
+}
+

akka-cluster-sharding/src/test/resources/reference.conf

@@ -1,6 +1,6 @@
 akka {
   actor {
-    serialize-creators = on
+    serialize-creators = off
     serialize-messages = on
     warn-about-java-serializer-usage = off
   }

akka-cluster-sharding/src/test/scala/akka/cluster/sharding/protobuf/ClusterShardingMessageSerializerSpec.scala

@@ -3,11 +3,10 @@
  */
 package akka.cluster.sharding.protobuf
 
-import akka.actor.{ ExtendedActorSystem }
+import akka.actor.ExtendedActorSystem
 import akka.testkit.AkkaSpec
 import akka.actor.Props
-import akka.cluster.sharding.ShardCoordinator
+import akka.cluster.sharding.{ Shard, ShardCoordinator, ShardRegion }
-import akka.cluster.sharding.Shard
 
 class ClusterShardingMessageSerializerSpec extends AkkaSpec {
   import ShardCoordinator.Internal._
@@ -28,7 +27,7 @@ class ClusterShardingMessageSerializerSpec extends AkkaSpec {
 
   "ClusterShardingMessageSerializer" must {
 
-    "be able to serializable ShardCoordinator snapshot State" in {
+    "be able to serialize ShardCoordinator snapshot State" in {
       val state = State(
         shards = Map("a" → region1, "b" → region2, "c" → region2),
         regions = Map(region1 → Vector("a"), region2 → Vector("b", "c"), region3 → Vector.empty[String]),
@@ -37,7 +36,7 @@ class ClusterShardingMessageSerializerSpec extends AkkaSpec {
       checkSerialization(state)
     }
 
-    "be able to serializable ShardCoordinator domain events" in {
+    "be able to serialize ShardCoordinator domain events" in {
       checkSerialization(ShardRegionRegistered(region1))
       checkSerialization(ShardRegionProxyRegistered(regionProxy1))
       checkSerialization(ShardRegionTerminated(region1))
@@ -46,7 +45,7 @@ class ClusterShardingMessageSerializerSpec extends AkkaSpec {
       checkSerialization(ShardHomeDeallocated("a"))
     }
 
-    "be able to serializable ShardCoordinator remote messages" in {
+    "be able to serialize ShardCoordinator remote messages" in {
       checkSerialization(Register(region1))
       checkSerialization(RegisterProxy(regionProxy1))
       checkSerialization(RegisterAck(region1))
@@ -61,21 +60,26 @@ class ClusterShardingMessageSerializerSpec extends AkkaSpec {
       checkSerialization(GracefulShutdownReq(region1))
     }
 
-    "be able to serializable PersistentShard snapshot state" in {
+    "be able to serialize PersistentShard snapshot state" in {
       checkSerialization(Shard.State(Set("e1", "e2", "e3")))
     }
 
-    "be able to serializable PersistentShard domain events" in {
+    "be able to serialize PersistentShard domain events" in {
       checkSerialization(Shard.EntityStarted("e1"))
       checkSerialization(Shard.EntityStopped("e1"))
     }
 
-    "be able to serializable GetShardStats" in {
+    "be able to serialize GetShardStats" in {
       checkSerialization(Shard.GetShardStats)
     }
 
-    "be able to serializable ShardStats" in {
+    "be able to serialize ShardStats" in {
       checkSerialization(Shard.ShardStats("a", 23))
     }
+
+    "be able to serialize StartEntity" in {
+      checkSerialization(ShardRegion.StartEntity("42"))
+      checkSerialization(ShardRegion.StartEntityAck("13", "37"))
+    }
   }
 }

akka-docs/src/main/paradox/java/cluster-sharding.md

@@ -267,12 +267,15 @@ are thereafter delivered to a new incarnation of the entity.
 
 The list of entities in each `Shard` can be made persistent (durable) by setting
 the `rememberEntities` flag to true in `ClusterShardingSettings` when calling 
-`ClusterSharding.start`. When configured to remember entities, whenever a `Shard` 
+`ClusterSharding.start` and making sure the `shardIdExtractor` handles
-is rebalanced onto another node or recovers after a crash it will recreate all the
+`Shard.StartEntity(EntityId)` which implies that a `ShardId` must be possible to
-entities which were previously running in that `Shard`. To permanently stop entities, 
+extract from the `EntityId`.
-a `Passivate` message must be sent to the parent of the entity actor, otherwise the
+
-entity will be automatically restarted after the entity restart backoff specified in 
+When configured to remember entities, whenever a `Shard` is rebalanced onto another
-the configuration.
+node or recovers after a crash it will recreate all the entities which were previously
+running in that `Shard`. To permanently stop entities, a `Passivate` message must be
+sent to the parent of the entity actor, otherwise the entity will be automatically
+restarted after the entity restart backoff specified in the configuration.
 
 When [Distributed Data mode](#cluster-sharding-mode) is used the identifiers of the entities are
 stored in @ref:[Durable Storage](distributed-data.md#ddata-durable) of Distributed Data. You may want to change the 

akka-docs/src/main/paradox/scala/cluster-sharding.md

@@ -270,12 +270,15 @@ are thereafter delivered to a new incarnation of the entity.
 
 The list of entities in each `Shard` can be made persistent (durable) by setting
 the `rememberEntities` flag to true in `ClusterShardingSettings` when calling
-`ClusterSharding.start`. When configured to remember entities, whenever a `Shard`
+`ClusterSharding.start` and making sure the `shardIdExtractor` handles
-is rebalanced onto another node or recovers after a crash it will recreate all the
+`Shard.StartEntity(EntityId)` which implies that a `ShardId` must be possible to
-entities which were previously running in that `Shard`. To permanently stop entities,
+extract from the `EntityId`.
-a `Passivate` message must be sent to the parent of the entity actor, otherwise the
+
-entity will be automatically restarted after the entity restart backoff specified in
+When configured to remember entities, whenever a `Shard` is rebalanced onto another
-the configuration.
+node or recovers after a crash it will recreate all the entities which were previously
+running in that `Shard`. To permanently stop entities, a `Passivate` message must be
+sent to the parent of the entity actor, otherwise the entity will be automatically
+restarted after the entity restart backoff specified in the configuration.
 
 When [Distributed Data mode](#cluster-sharding-mode) is used the identifiers of the entities are
 stored in @ref:[Durable Storage](distributed-data.md#ddata-durable) of Distributed Data. You may want to change the

akka-docs/src/main/paradox/scala/project/migration-guide-2.4.x-2.5.x.md

@@ -479,6 +479,18 @@ Note that the stored @ref:[Remembering Entities](../cluster-sharding.md#cluster-
 be migrated to the `data` mode. Such entities must be started again in some other way when using
 `ddata` mode.
 
+### Cluster Sharding remember entities
+
+To use *remember entities* with cluster sharding there are now an additional requirement added: the
+`extractShardId` must be able to extract the shard id from the message `Shard.StartEntity(EntityId)`.
+This is implies that it must be possible to calculate a shard id from an entity id when using remember
+entities.
+
+This was added to be able to gracefully handle when persisted locations of entities does not match
+where the entities should live when a shard region starts up. Such states could be cause by changing
+the `extractShardId` logic and restart a system using *remember entities*.
+
+
 ### Cluster Management Command Line Tool
 
 There is a new cluster management tool with HTTP API that has the same functionality as the command line tool.