Akka Best Practices

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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-best-practicesThe 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
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Its description: Critical Akka.NET best practices including EventStream vs DistributedPubSub, supervision strategies, error handling, Props vs DependencyResolver, work distribution patterns, and cluster/local mode abstractions for…

---
name: akka-net-best-practices
description: Critical Akka.NET best practices including EventStream vs DistributedPubSub, supervision strategies, error handling, Props vs DependencyResolver, work distribution patterns, and cluster/local mode abstractions for testability.
user-invocable: false
---

# Akka.NET Best Practices

## When to Use This Skill

Use this skill when:
- Designing actor communication patterns
- Deciding between EventStream and DistributedPubSub
- Implementing error handling in actors
- Understanding supervision strategies
- Choosing between Props patterns and DependencyResolver
- Designing work distribution across nodes
- Creating testable actor systems that can run with or without cluster infrastructure
- Abstracting over Cluster Sharding for local testing scenarios

## Reference Files

- [work-distribution-patterns.md](work-distribution-patterns.md): Database queues, Akka.Streams throttling, outbox pattern
- [cluster-local-abstractions.md](cluster-local-abstractions.md): GenericChildPerEntityParent, IPubSubMediator, execution mode wiring
- [async-cancellation-patterns.md](async-cancellation-patterns.md): Actor-scoped CancellationToken, linked CTS, timeout handling

---

## 1. EventStream vs DistributedPubSub

### Critical: EventStream is LOCAL ONLY

`Context.System.EventStream` is **local to a single ActorSystem process**. It does NOT work across cluster nodes.

```csharp
// BAD: This only works on a single server
// When you add a second server, subscribers on server 2 won't receive events from server 1
Context.System.EventStream.Subscribe(Self, typeof(PostCreated));
Context.System.EventStream.Publish(new PostCreated(postId, authorId));
```

**When EventStream is appropriate:**
- Logging and diagnostics within a single process
- Local event bus for truly single-process applications
- Development/testing scenarios

### Use DistributedPubSub for Multi-Node

For events that must reach actors across multiple cluster nodes, use `Akka.Cluster.Tools.PublishSubscribe`:

```csharp
using Akka.Cluster.Tools.PublishSubscribe;

public class TimelineUpdatePublisher : ReceiveActor
{
    private readonly IActorRef _mediator;

    public TimelineUpdatePublisher()
    {
        // Get the DistributedPubSub mediator
        _mediator = DistributedPubSub.Get(Context.System).Mediator;

        Receive<PublishTimelineUpdate>(msg =>
        {
            // Publish to a topic - reaches all subscribers across all nodes
            _mediator.Tell(new Publish($"timeline:{msg.UserId}", msg.Update));
        });
    }
}
```

### Akka.Hosting Configuration for DistributedPubSub

```csharp
builder.WithDistributedPubSub(role: null); // Available on all roles, or specify a role
```

### Topic Design Patterns

| Pattern | Topic Format | Use Case |
|---------|--------------|----------|
| Per-user | `timeline:{userId}` | Timeline updates, notifications |
| Per-entity | `post:{postId}` | Post engagement updates |
| Broadcast | `system:announcements` | System-wide notifications |
| Role-based | `workers:rss-poller` | Work distribution |

---

## 2. Supervision Strategies

### Key Clarification: Supervision is for CHILDREN

A supervision strategy defined on an actor dictates **how that actor supervises its children**, NOT how the actor itself is supervised.

```csharp
public class ParentActor : ReceiveActor
{
    // This strategy applies to children of ParentActor, NOT to ParentActor itself
    protected override SupervisorStrategy SupervisorStrategy()
    {
        return new OneForOneStrategy(
            maxNrOfRetries: 10,
            withinTimeRange: TimeSpan.FromSeconds(30),
            decider: ex => ex switch
            {
                ArithmeticException => Directive.Resume,
                NullReferenceException => Directive.Restart,
                ArgumentException => Directive.Stop,
                _ => Directive.Escalate
            });
    }
}
```

### Default Supervision Strategy

The default `OneForOneStrategy` already includes rate limiting:
- **10 restarts within 1 second** = actor is permanently stopped
- This prevents infinite restart loops

**You rarely need a custom strategy** unless you have specific requirements.

### When to Define Custom Supervision

**Good reasons:**
- Actor throws exceptions indicating irrecoverable state corruption -> Restart
- Actor throws exceptions that should NOT cause restart (expected failures) -> Resume
- Child failures should affect siblings -> Use `AllForOneStrategy`
- Need different retry limits than the default

**Bad reasons:**
- "Just to be safe" - the default is already safe
- Don't understand what the actor does - understand it first

---

## 3. Error Handling: Supervision vs Try-Catch

### When to Use Try-Catch (Most Cases)

**Use try-catch when:**
- The failure is **expected** (network timeout, invalid input, external service down)
- You know **exactly why** the exception occurred
- You can handle it **gracefully** (retry, return error response, log and continue)
- Restarting would **not help** (same error would occur again)

```csharp
public class RssFeedPollerActor : ReceiveActor
{
    public RssFeedPollerActor()
    {
        ReceiveAsync<PollFeed>(async msg =>
        {
            try
            {
                var feed = await _httpClient.GetStringAsync(msg.FeedUrl);
                var items = ParseFeed(feed);
                // Process items...
            }
            catch (HttpRequestException ex)
            {
                // Expected failure - log and schedule retry
                _log.Warning("Feed {Url} unavailable: {Error}", msg.FeedUrl, ex.Message);
                Context.System.Scheduler.ScheduleTellOnce(
                    TimeSpan.FromMinutes(5), Self, msg, Self);
            }
            catch (XmlException ex)
            {
                // Invalid feed format - log and mark as bad
                _log.Error("Feed {Url} has invalid format: {Error}", msg.FeedUrl, ex.Message);
                Sender.Tel

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

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 Best Practices

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