Outbox Kafka Dispatch

ID: dispatch.outbox.kafka
Name: Outbox Kafka dispatch
Maturity: GA
Summary: Publish leased outbox envelopes to Kafka topics with contract headers via UseKafkaDispatch.

What It Does

Registers TransportOutboxDispatchModule with KafkaTransportModule. Outbox processor produces records to the configured topic with key from topic metadata, resolver, or contract name. Payload and headers follow the same mapping as other transport outbox adapters.

Packages

Package	Role
`LiteBus.Outbox.Dispatch.Kafka`	Registration glue
`LiteBus.Outbox.Dispatch`	Shared dispatcher
`LiteBus.Transport.Kafka`	Confluent adapter

Requires

dispatch.transport-core
transport.kafka
durable-core.outbox

Invariants

Default hook failure policy: CompleteDespiteHookFailure.
At-least-once: consumers must deduplicate using headers or business logic.
No broker-level deduplication of republished outbox rows after processor crash.

Non-Goals

Does not use Kafka idempotent producer settings as outbox exactly-once guarantee.
Does not consume from topics.

Public Surface

services.AddLiteBus(litebus =>
{
    litebus.AddKafkaTransport(new KafkaTransportOptions
    {
        BootstrapServers = "localhost:9092",
        ClientId = "orders-outbox-dispatch"
    });

    litebus.AddOutbox(outbox =>
    {
        outbox.EnableOutboxProcessor();
        outbox.UseKafkaDispatch(
            options =>
            {
                options.DefaultDestination = "orders.events";
            });
    });
});

API	Role
`OutboxModuleBuilder.UseKafkaDispatch(Action<TransportOutboxDispatcherOptions>)`	Registers outbox transport dispatcher that requires the root Kafka transport
`TransportOutboxDispatchModule.DefaultHookFailurePolicy`	Defaults to `CompleteDespiteHookFailure`
`TransportOutboxDispatcher.DispatchAsync(OutboxEnvelope, CancellationToken)`	Publishes outbox payload and headers to Kafka

Route resolution: tenant strategy, then envelope Topic, then resolver, then contract name.

Observability

Signal	Detail
`send {destination}`	Topic destination, `messaging.kafka.message.key`, and message id attributes
`litebus.transport.circuit_breaker.open` / `failure_count`	Tag `litebus.transport.broker="kafka"`
`litebus.outbox.processor.published` / `failed`	Terminal outcomes after Kafka publish attempt
`litebus.outbox.processor.dispatch_duration`	Includes producer send latency

Failure paths increment circuit breaker when broker is unreachable (KafkaDispatchFailureIntegrationTests).

Deep Docs

Test Coverage

Covered

Test method	Project
`OutboxDispatchExtensions_ShouldRegisterTransportDispatcher`	`LiteBus.Durable.IntegrationTests` (`Registration/`) (Kafka Theory case)
`ProcessPendingAsync_ShouldPublishEnvelopeToKafkaTopic`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Outbox/Kafka/`)
`ProcessPendingAsync_WhenTopicMissing_ShouldUseContractNameAsRoute`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Outbox/Kafka/`)
`ProcessPendingAsync_WhenBrokerUnreachable_ShouldMarkFailedWithVisibleAfter`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Outbox/Kafka/`)
`ProcessPendingAsync_WhenCircuitBreakerOpen_ShouldNotPublish`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Outbox/Kafka/`)

Untested

After-dispatch hook failure path with CompleteDespiteHookFailure.
Tenant route strategy branch and custom resolver branch.
Idempotent producer settings as an exactly-once guarantee, which is outside dispatch guarantees.

Out-of-Scope

Kafka idempotent producer as outbox exactly-once guarantee
Consuming from Kafka topics