Stratara.Outbox.RabbitMQ 4.4.4

Stratara.Outbox.RabbitMQ

Derived. The behaviour described here is specified under openspec/specs/. Those specifications are the source; this page explains and illustrates them.

License: MIT.

Outbox-pattern command + event dispatch for the Stratara event-sourced stack with a RabbitMQ message-bus implementation. Contains the write-side dispatchers, the outbox-retry worker, the read-side mediator command worker, the RabbitMQ bus, and the ProjectionReplayState that coordinates dispatch skip during projection replay — shared over Redis where a connection is registered, held in process otherwise. Azure Service Bus ships separately as Stratara.Outbox.AzureServiceBus.

What's in the box

Quick start

// In your API host:
builder.AddMessaging();                          // IMessageBus + MessagingOptions binding
builder.Services
    .AddOutboxDispatcher()                       // CommandOutboxDispatcher + EventBundleOutboxDispatcher + ProjectionReplayState
    .AddOutboxWorker(builder.Configuration);     // OutboxWorker hosted service (only if this host owns retries)

// In your command worker:
builder.Services
    .AddMediatorWorker();                        // MediatorCommandWorker hosted service

The dispatchers consult IProjectionReplayState.IsReplayActive before each publish and skip dispatch (writing to the outbox table only) while a replay is in progress. They also record the outbox.published counter for what the broker accepted — the worker counts nothing, because only the dispatcher knows what went out.

The replay marking and its progress counters are held on the lease configured by ProjectionReplayOptions.LeaseSeconds (default 300), which the replay renews every time it reports progress. A replay whose host is killed stops renewing it and the marking lapses on its own, instead of suppressing publication indefinitely. AddProjectionReplayState() reads the options from the ProjectionReplay section of the host's configuration; services.Configure<ProjectionReplayOptions>(...) after that call takes precedence. A lease of zero or less fails the host at start. Set it longer than the slowest stretch between two progress reports — too short lets the marking lapse while the replay is still running.

A drain cycle takes one batch of each kind and ends. Rows the broker would not accept stay in the table for the next interval; a cycle never re-reads what it just failed to publish, so an unreachable broker or a suppressed drain cannot turn a cycle into a loop over the same rows.

Multi-instance outbox workers

AddOutboxWorker registers NullOutboxLock as the default IOutboxLock — a no-op that preserves the single-instance assumption. For multi-replica deployments call AddRedisOutboxLock() afterwards; it replaces the no-op with a Redis-leased lock (SET stratara:outbox:lock NX EX) so only one replica drains at a time:

builder.AddCaching();                              // registers IConnectionMultiplexer
builder.Services
    .AddOutboxDispatcher()
    .AddOutboxWorker(builder.Configuration)
    .AddRedisOutboxLock();                         // multi-replica safe

The lease defaults to 60 s (OutboxOptions.LockLeaseSeconds). Tune it so it exceeds the worst-case drain duration; otherwise the lock can expire mid-cycle and a peer may start a concurrent drain. Outbox semantics are still at-least-once, so a duplicate publish is recoverable provided handlers stay idempotent.

Dependencies

• Stratara.Abstractions — for ICommand, IEvent, IMessageBus, ICommandOutboxDispatcher, IEventBundleOutboxDispatcher, IProjectionReplayState, IMessagingIdentifier, IWriteUnitOfWork (used at runtime via the outbox repository).
• Stratara.Contracts — for EventBundle + CommandEnvelope messages.
• Stratara.Mediator — MediatorCommandWorker dispatches into the in-process IMediator.
• Stratara.Sessions — dispatcher hydrates CommandEnvelope from the current session context.
• Stratara.Shared — for messaging primitives, resilience pipeline names, mapping helpers, and the diagnostics base.
• RabbitMQ.Client, StackExchange.Redis (only used when a connection is registered: shared replay state, optional outbox lock).
• Microsoft.Extensions.Hosting.Abstractions + Microsoft.Extensions.Options.ConfigurationExtensions — for hosted services + options binding.

The outbox dispatcher persists rows through IWriteUnitOfWork.CreateOutboxRepository — that interface lives in Stratara.Abstractions, but the concrete implementation comes from Stratara.EventSourcing.EntityFrameworkCore. Reference that package alongside this one to get a working stack.