Inbox Kafka Dispatch

ID: dispatch.inbox.kafka
Name: Inbox Kafka dispatch
Maturity: GA
Summary: Publish leased inbox envelopes to Kafka topics through UseKafkaDispatch with manual offset semantics on the consumer side.

What It Does

Registers TransportInboxDispatchModule with KafkaTransportModule. DefaultDestination is the topic; route is the record key (defaults via contract name or custom resolver). Kafka transport uses manual offset commit on consume; dispatch publish does not commit offsets.

Pair Kafka dispatch with inbox idempotency and idempotent handlers. Kafka has no queue-style lease equivalent on the broker.

Packages

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

Requires

dispatch.transport-core
transport.kafka
durable-core.inbox

Invariants

Consumer offset commit happens on ingress/consume path, not dispatch.
Failed consume records seek back for in-session retry (transport behavior).
Handlers must tolerate redelivery after rebalance or uncommitted offsets.

Non-Goals

Does not implement Kafka transactions for consume-process-produce loops.
Does not manage topic creation or schema registry.

Public Surface

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

    litebus.AddInbox(inbox =>
    {
        inbox.EnableInboxProcessor();
        inbox.UseKafkaDispatch(
            options =>
            {
                options.DefaultDestination = "orders.commands";
                options.ResolveRoute = envelope => envelope.ContractName;
            });
    });
});

API	Role
`InboxModuleBuilder.UseKafkaDispatch(Action<TransportInboxDispatcherOptions>)`	Registers inbox transport dispatcher that requires the root Kafka transport
`TransportInboxDispatcher.DispatchAsync(InboxEnvelope, CancellationToken)`	Publishes inbox lease payload and headers to Kafka

KafkaTransportOptions:

Property	Default	Role
`BootstrapServers`	required	Kafka bootstrap server list
`ClientId`	`null`	Producer and consumer client id
`ConsumerGroupId`	`litebus-transport`	Group id for transport consumer side
`MessageTimeoutMs`	`null`	Producer local message timeout override
`SeekFailureBackoffInitial`	`00:00:00.250`	Initial seek retry delay
`SeekFailureBackoffMax`	`00:00:30`	Max seek retry delay
`SeekFailureBackoffMultiplier`	`2.0`	Seek retry multiplier

Observability

Signal	Detail
`send {destination}`	Tags include topic as `messaging.destination.name`, record key as `messaging.kafka.message.key`
`litebus.transport.circuit_breaker.*`	Broker tag `kafka`
`process {destination}`	Not emitted on dispatch; consumer/ingress path only
`litebus.inbox.processor.*`	Standard inbox processor counters and dispatch duration histogram

Register Kafka transport metrics through AddLiteBusTransportMetrics() from LiteBus.Transport.Extensions.OpenTelemetry.

Deep Docs

Architecture.md: Kafka at-least-once semantics

Test Coverage

Covered

Test method	Project
`InboxDispatchExtensions_ShouldRegisterTransportDispatcher`	`LiteBus.Durable.IntegrationTests` (`Registration/`) (Kafka Theory case)
`ProcessPendingAsync_ShouldPublishLeasedEnvelopeToKafkaTopic`	`LiteBus.Durable.IntegrationTests` (`Dispatch/Inbox/Kafka/`)

Untested

Inbox dispatch failure on unreachable brokers.
Route override and tenant route strategy coverage.
Kafka transaction usage, which is not part of current dispatcher contracts.

Out-of-Scope

Kafka transactions for consume-process-produce loops
Topic creation and schema registry management