Outbox

Definition: The Outbox Pattern solves the problem of reliably updating a database and publishing an event/message.
The service stores the business change and an “outbox event” in the same database transaction, then a separate process publishes the event.

Without Outbox

Update DB ✅
Publish Kafka message ❌

Now the database changed but nobody knows about it.

With Outbox

DB transaction:
    Update Order
    Insert Outbox Event
          ↓
    Commit ✅
          ↓
Outbox Publisher
          ↓
Kafka

Examples:

1. Create order + OrderCreated event.
2. Register user + UserRegistered event.
3. Change payment status + PaymentCompleted event.

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Database My-Journey-In-Codeless