Akka Hosting Actor Patterns

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Five audit layers

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CLAUDE.md

Audit 0.4.1 · source sha 871f73ffcae3 · 18 Oct 2026Report an issue or request a re-scan

• PublisherAaronontheweb GitHub userOwner of the repository this skill is read from
• Source folderAaronontheweb/dotnet-skills/skills/akka-hosting-actor-patternsThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict871f73ffcae3A new audit runs when the source changes
• Repository statusNot archivedLast push 7 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: Patterns for building entity actors with Akka.Hosting - GenericChildPerEntityParent, message extractors, cluster sharding abstraction, akka-reminders, and ITimeProvider. Supports both local testing and clustered…

---
name: akka-hosting-actor-patterns
description: Patterns for building entity actors with Akka.Hosting - GenericChildPerEntityParent, message extractors, cluster sharding abstraction, akka-reminders, and ITimeProvider. Supports both local testing and clustered production modes.
user-invocable: false
---

# Akka.Hosting Actor Patterns

## When to Use This Skill

Use this skill when:
- Building entity actors that represent domain objects (users, orders, invoices, etc.)
- Need actors that work in both unit tests (no clustering) and production (cluster sharding)
- Setting up scheduled tasks with akka-reminders
- Registering actors with Akka.Hosting extension methods
- Creating reusable actor configuration patterns

## Core Principles

1. **Execution Mode Abstraction** - Same actor code runs locally (tests) or clustered (production)
2. **GenericChildPerEntityParent for Local** - Mimics sharding semantics without cluster overhead
3. **Message Extractors for Routing** - Reuse Akka.Cluster.Sharding's IMessageExtractor interface
4. **Akka.Hosting Extension Methods** - Fluent configuration that composes well
5. **ITimeProvider for Testability** - Use ActorSystem.Scheduler instead of DateTime.Now

## Execution Modes

Define an enum to control actor behavior:

```csharp
/// <summary>
/// Determines how Akka.NET should be configured
/// </summary>
public enum AkkaExecutionMode
{
    /// <summary>
    /// Pure local actor system - no remoting, no clustering.
    /// Use GenericChildPerEntityParent instead of ShardRegion.
    /// Ideal for unit tests and simple scenarios.
    /// </summary>
    LocalTest,

    /// <summary>
    /// Full clustering with ShardRegion.
    /// Use for integration testing and production.
    /// </summary>
    Clustered
}
```

## GenericChildPerEntityParent

A lightweight parent actor that routes messages to child entities, mimicking cluster sharding semantics without requiring a cluster:

```csharp
using Akka.Actor;
using Akka.Cluster.Sharding;

/// <summary>
/// A generic "child per entity" parent actor.
/// </summary>
/// <remarks>
/// Reuses Akka.Cluster.Sharding's IMessageExtractor for consistent routing.
/// Ideal for unit tests where clustering overhead is unnecessary.
/// </remarks>
public sealed class GenericChildPerEntityParent : ReceiveActor
{
    public static Props CreateProps(
        IMessageExtractor extractor,
        Func<string, Props> propsFactory)
    {
        return Props.Create(() =>
            new GenericChildPerEntityParent(extractor, propsFactory));
    }

    private readonly IMessageExtractor _extractor;
    private readonly Func<string, Props> _propsFactory;

    public GenericChildPerEntityParent(
        IMessageExtractor extractor,
        Func<string, Props> propsFactory)
    {
        _extractor = extractor;
        _propsFactory = propsFactory;

        ReceiveAny(message =>
        {
            var entityId = _extractor.EntityId(message);
            if (entityId is null) return;

            // Get existing child or create new one
            Context.Child(entityId)
                .GetOrElse(() => Context.ActorOf(_propsFactory(entityId), entityId))
                .Forward(_extractor.EntityMessage(message));
        });
    }
}
```

## Message Extractors

Create extractors that implement `IMessageExtractor` from Akka.Cluster.Sharding:

```csharp
using Akka.Cluster.Sharding;

/// <summary>
/// Routes messages to entity actors based on a strongly-typed ID.
/// </summary>
public sealed class OrderMessageExtractor : HashCodeMessageExtractor
{
    public const int DefaultShardCount = 40;

    public OrderMessageExtractor(int maxNumberOfShards = DefaultShardCount)
        : base(maxNumberOfShards)
    {
    }

    public override string? EntityId(object message)
    {
        return message switch
        {
            IWithOrderId msg => msg.OrderId.Value.ToString(),
            _ => null
        };
    }
}

// Define an interface for messages that target a specific entity
public interface IWithOrderId
{
    OrderId OrderId { get; }
}

// Use strongly-typed IDs
public readonly record struct OrderId(Guid Value)
{
    public static OrderId New() => new(Guid.NewGuid());
    public override string ToString() => Value.ToString();
}
```

## Akka.Hosting Extension Methods

Create extension methods that abstract the execution mode:

```csharp
using Akka.Cluster.Hosting;
using Akka.Cluster.Sharding;
using Akka.Hosting;

public static class OrderActorHostingExtensions
{
    /// <summary>
    /// Adds OrderActor with support for both local and clustered modes.
    /// </summary>
    public static AkkaConfigurationBuilder WithOrderActor(
        this AkkaConfigurationBuilder builder,
        AkkaExecutionMode executionMode = AkkaExecutionMode.Clustered,
        string? clusterRole = null)
    {
        if (executionMode == AkkaExecutionMode.LocalTest)
        {
            // Non-clustered mode: Use GenericChildPerEntityParent
            builder.WithActors((system, registry, resolver) =>
            {
                var parent = system.ActorOf(
                    GenericChildPerEntityParent.CreateProps(
                        new OrderMessageExtractor(),
                        entityId => resolver.Props<OrderActor>(entityId)),
                    "orders");

                registry.Register<OrderActor>(parent);
            });
        }
        else
        {
            // Clustered mode: Use ShardRegion
            builder.WithShardRegion<OrderActor>(
                "orders",
                (system, registry, resolver) =>
                    entityId => resolver.Props<OrderActor>(entityId),
                new OrderMessageExtractor(),
                new ShardOptions
                {
                    StateStoreMode = StateStoreMode.DData,
                    Role = clusterRole
                });
        }

        return builder;
    }
}
```

## Composing Multiple Actors

Create a convenience method that registers all domain actors:

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git clone https://github.com/Aaronontheweb/dotnet-skills
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Works in

1. 2026-10-18
   ✓SAFE B 89 / 100

   first audit · source 871f73ffcae3

Questions about Akka Hosting Actor Patterns

• github.com/Aaronontheweb/dotnet-skills/tree/master/skills/akka-h — the audited source at commit 871f73ffcae3 and every finding aboveObserved · 18 Oct 2026

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