Backport of the feature called ClusterDistribution in Lagom

docs/articles/clustering/cluster-sharded-daemon-process.md

@@ -0,0 +1,51 @@
+# Sharded Daemon Process
+
+> [!WARNING]
+>This module is currently marked as [may change](../utilities/may-change.md) because it is a new feature that
+>needs feedback from real usage before finalizing the API. This means that API or semantics can change without
+>warning or deprecation period. It is also not recommended to use this module in production just yet.
+
+## Introduction
+
+Sharded Daemon Process provides a way to run `N` actors, each given a numeric id starting from `0` that are then kept alive
+and balanced across the cluster. When a rebalance is needed the actor is stopped and, triggered by a keep alive running on 
+all nodes, started on a new node (the keep alive should be seen as an implementation detail and may change in future versions).
+
+The intended use case is for splitting data processing workloads across a set number of workers that each get to work on a subset
+of the data that needs to be processed. This is commonly needed to create projections based on the event streams available
+from all the [Persistent Actors](../persistence/event-sourcing.md) in a CQRS application. Events are tagged with one out of `N` tags
+used to split the workload of consuming and updating a projection between `N` workers.
+
+For cases where a single actor needs to be kept alive see [Cluster Singleton](cluster-singleton.md)
+
+## Basic example
+
+To set up a set of actors running with Sharded Daemon process each node in the cluster needs to run the same initialization
+when starting up:
+
+```csharp
+class TagProcessor : ReceiveActor
+{
+    public string Tag { get; }
+
+    public static Props Props(string tag) =>
+        Actor.Props.Create(() => new TagProcessor(tag));
+
+    public TagProcessor(string tag) => Tag = tag;
+
+    protected override void PreStart()
+    {
+        // start the processing ...
+        base.PreStart();
+        Context.System.Log.Debug("Starting processor for tag {0}", Tag);
+    }
+}
+
+var tags = new[] { "tag-1", "tag-2", "tag-3" };
+ShardedDaemonProcess.Get(Sys).Init("TagProcessors", tags.Length, id => TagProcessor.Props(tags[id]));
+```
+
+## Scalability  
+
+This cluster tool is intended for small numbers of consumers and will not scale well to a large set. In large clusters 
+it is recommended to limit the nodes the sharded daemon process will run on using a role.

src/contrib/cluster/Akka.Cluster.Sharding.Tests.MultiNode/ShardedDaemonProcessSpec.cs

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+//-----------------------------------------------------------------------
+// <copyright file="ClusterShardingSpec.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2020 Lightbend Inc. <http://www.lightbend.com>
+//     Copyright (C) 2013-2020 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// </copyright>
+//-----------------------------------------------------------------------
+
+using System;
+using System.Linq;
+using Akka.Actor;
+using Akka.Cluster.TestKit;
+using Akka.Cluster.Tools.Singleton;
+using Akka.Configuration;
+using Akka.Remote.TestKit;
+using FluentAssertions;
+
+namespace Akka.Cluster.Sharding.Tests.MultiNode
+{
+    public class ShardedDaemonProcessSpecConfig : MultiNodeConfig
+    {
+        public RoleName First { get; }
+        public RoleName Second { get; }
+        public RoleName Third { get; }
+
+        public ShardedDaemonProcessSpecConfig()
+        {
+            First = Role("first");
+            Second = Role("second");
+            Third = Role("third");
+
+            CommonConfig = DebugConfig(false)
+                .WithFallback(ConfigurationFactory.ParseString(@"
+                    akka.loglevel = INFO
+                    akka.cluster.sharded-daemon-process {{
+                      sharding {{
+                        # First is likely to be ignored as shard coordinator not ready
+                        retry-interval = 0.2s
+                      }}
+                      # quick ping to make test swift
+                      keep-alive-interval = 1s
+                    }}
+                "))
+                .WithFallback(ClusterSharding.DefaultConfig())
+                .WithFallback(ClusterSingletonManager.DefaultConfig())
+                .WithFallback(MultiNodeClusterSpec.ClusterConfig());
+        }
+    }
+
+    public class ShardedDaemonProcessMultiNode : ShardedDaemonProcessSpec
+    {
+        public ShardedDaemonProcessMultiNode() : this(new ShardedDaemonProcessSpecConfig()) { }
+        protected ShardedDaemonProcessMultiNode(ShardedDaemonProcessSpecConfig config) : base(config, typeof(ShardedDaemonProcessMultiNode)) { }
+    }
+
+    public abstract class ShardedDaemonProcessSpec : MultiNodeClusterSpec
+    {
+        private readonly ShardedDaemonProcessSpecConfig _config;
+
+        protected ShardedDaemonProcessSpec(ShardedDaemonProcessSpecConfig config, Type type)
+            : base(config, type)
+        {
+            _config = config;
+        }
+
+        [MultiNodeFact]
+        public void ShardedDaemonProcess_Specs()
+        {
+            ShardedDaemonProcess_Should_Init_Actor_Set();
+        }
+
+        public void ShardedDaemonProcess_Should_Init_Actor_Set()
+        {
+            // HACK
+            RunOn(() => FormCluster(_config.First, _config.Second, _config.Third), _config.First);
+
+            var probe = CreateTestProbe();
+            ShardedDaemonProcess.Get(Sys).Init("the-fearless", 4, id => ProcessActor.Props(id, probe.Ref));
+            EnterBarrier("actor-set-initialized");
+
+            RunOn(() =>
+            {
+                var startedIds = Enumerable.Range(0, 4).Select(_ =>
+                {
+                    var evt = probe.ExpectMsg<ProcessActorEvent>(TimeSpan.FromSeconds(5));
+                    evt.Event.Should().Be("Started");
+                    return evt.Id;
+                }).ToList();
+                startedIds.Count.Should().Be(4);
+            }, _config.First);
+            EnterBarrier("actor-set-started");
+        }
+
+        private void FormCluster(RoleName first, params RoleName[] rest)
+        {
+            RunOn(() =>
+            {
+                Cluster.Join(GetAddress(first));
+                AwaitAssert(() =>
+                {
+                    Cluster.State.Members.Select(i => i.UniqueAddress).Should().Contain(Cluster.SelfUniqueAddress);
+                    Cluster.State.Members.Select(i => i.Status).Should().OnlyContain(i => i == MemberStatus.Up);
+                });
+            }, first);
+            EnterBarrier(first.Name + "-joined");
+
+            foreach (var node in rest)
+            {
+                RunOn(() =>
+                {
+                    Cluster.Join(GetAddress(first));
+                    AwaitAssert(() =>
+                    {
+                        Cluster.State.Members.Select(i => i.UniqueAddress).Should().Contain(Cluster.SelfUniqueAddress);
+                        Cluster.State.Members.Select(i => i.Status).Should().OnlyContain(i => i == MemberStatus.Up);
+                    });
+                }, node);
+            }
+            EnterBarrier("all-joined");
+        }
+    }
+
+    internal class ProcessActor : UntypedActor
+    {
+        #region Protocol
+
+        [Serializable]
+        public sealed class Stop
+        {
+            public static readonly Stop Instance = new Stop();
+            private Stop() { }
+        }
+
+        #endregion
+
+        public static Props Props(int id, IActorRef probe) =>
+            Actor.Props.Create(() => new ProcessActor(id, probe));
+
+        public ProcessActor(int id, IActorRef probe)
+        {
+            Probe = probe;
+            Id = id;
+        }
+
+        public IActorRef Probe { get; }
+        public int Id { get; }
+
+        protected override void PreStart()
+        {
+            base.PreStart();
+            Probe.Tell(new ProcessActorEvent(Id, "Started"));
+        }
+
+        protected override void OnReceive(object message)
+        {
+            if (message is Stop)
+            {
+                Probe.Tell(new ProcessActorEvent(Id, "Stopped"));
+                Context.Stop(Self);
+            }
+        }
+    }
+
+    internal sealed class ProcessActorEvent
+    {
+        public ProcessActorEvent(int id, object @event)
+        {
+            Id = id;
+            Event = @event;
+        }
+
+        public int Id { get; }
+        public object Event { get; }
+    }
+}

src/contrib/cluster/Akka.Cluster.Sharding.Tests/ShardedDaemonProcessSpec.cs

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+//-----------------------------------------------------------------------
+// <copyright file="ClusterSharding.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2020 Lightbend Inc. <http://www.lightbend.com>
+//     Copyright (C) 2013-2020 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// </copyright>
+//-----------------------------------------------------------------------
+
+using System;
+using System.Linq;
+using Akka.Actor;
+using Akka.Cluster.Tools.Singleton;
+using Akka.Configuration;
+using Akka.TestKit;
+using Xunit;
+
+namespace Akka.Cluster.Sharding.Tests
+{
+    public class ShardedDaemonProcessSpec : AkkaSpec
+    {
+        private sealed class Stop
+        {
+            public static Stop Instance { get; } = new Stop();
+            private Stop() { }
+        }
+
+        private sealed class Started
+        {
+            public int Id { get; }
+            public IActorRef SelfRef { get; }
+
+            public Started(int id, IActorRef selfRef)
+            {
+                Id = id;
+                SelfRef = selfRef;
+            }
+        }
+
+        private class MyActor : UntypedActor
+        {
+            public int Id { get; }
+            public IActorRef Probe { get; }
+
+            public static Props Props(int id, IActorRef probe) =>
+                Actor.Props.Create(() => new MyActor(id, probe));
+
+            public MyActor(int id, IActorRef probe)
+            {
+                Id = id;
+                Probe = probe;
+            }
+
+            protected override void PreStart()
+            {
+                base.PreStart();
+                Probe.Tell(new Started(Id, Context.Self));
+            }
+
+            protected override void OnReceive(object message)
+            {
+                if (message is Stop _)
+                    Context.Stop(Self);
+            }
+        }
+
+        private static Config GetConfig()
+        {
+            return ConfigurationFactory.ParseString(@"
+                akka.actor.provider = cluster
+                akka.remote.dot-netty.tcp.port = 0
+                akka.remote.dot-netty.tcp.hostname = 127.0.0.1
+
+                # ping often/start fast for test
+                akka.cluster.sharded-daemon-process.keep-alive-interval = 1s
+
+                akka.coordinated-shutdown.terminate-actor-system = off
+                akka.coordinated-shutdown.run-by-actor-system-terminate = off")                
+                .WithFallback(ClusterSharding.DefaultConfig())
+                .WithFallback(ClusterSingletonProxy.DefaultConfig());
+        }
+
+        public ShardedDaemonProcessSpec()
+            : base(GetConfig())
+        { }
+
+        [Fact]
+        public void ShardedDaemonProcess_must_have_a_single_node_cluster_running_first()
+        {
+            var probe = CreateTestProbe();
+            Cluster.Get(Sys).Join(Cluster.Get(Sys).SelfAddress);
+            probe.AwaitAssert(() => Cluster.Get(Sys).SelfMember.Status.ShouldBe(MemberStatus.Up), TimeSpan.FromSeconds(3));
+        }
+
+        [Fact]
+        public void ShardedDaemonProcess_must_start_N_actors_with_unique_ids()
+        {
+            Cluster.Get(Sys).Join(Cluster.Get(Sys).SelfAddress);
+
+            var probe = CreateTestProbe();
+            ShardedDaemonProcess.Get(Sys).Init("a", 5, id => MyActor.Props(id, probe.Ref));
+
+            var started = probe.ReceiveN(5);
+            started.Count.ShouldBe(5);
+        }
+
+        [Fact]
+        public void ShardedDaemonProcess_must_restart_actors_if_they_stop()
+        {
+            Cluster.Get(Sys).Join(Cluster.Get(Sys).SelfAddress);
+
+            var probe = CreateTestProbe();
+            ShardedDaemonProcess.Get(Sys).Init("stop", 2, id => MyActor.Props(id, probe.Ref));
+
+            foreach (var started in Enumerable.Range(0, 2).Select(_ => probe.ExpectMsg<Started>()))
+                started.SelfRef.Tell(Stop.Instance);
+
+            // periodic ping every 1s makes it restart
+            Enumerable.Range(0, 2).Select(_ => probe.ExpectMsg<Started>(TimeSpan.FromSeconds(3)));
+        }
+
+        [Fact]
+        public void ShardedDaemonProcess_must_not_run_if_the_role_does_not_match_node_role()
+        {
+            Cluster.Get(Sys).Join(Cluster.Get(Sys).SelfAddress);
+
+            var probe = CreateTestProbe();
+            var settings = ShardedDaemonProcessSettings.Create(Sys).WithShardingSettings(ClusterShardingSettings.Create(Sys).WithRole("workers"));
+            ShardedDaemonProcess.Get(Sys).Init("roles", 3, id => MyActor.Props(id, probe.Ref), settings);
+
+            probe.ExpectNoMsg();
+        }
+    }
+}

src/contrib/cluster/Akka.Cluster.Sharding/ShardRegion.cs

@@ -117,7 +117,7 @@ public override int GetHashCode()
         /// to start(it does not guarantee the entity successfully started)
         /// </summary>
         [Serializable]
-        public sealed class StartEntityAck : IClusterShardingSerializable
+        public sealed class StartEntityAck : IClusterShardingSerializable, IDeadLetterSuppression
         {
             /// <summary>
             /// An identifier of a newly started entity. Unique in scope of a given shard.