ASP.NET Core Web API Interview Question #190

What is the Outbox pattern?

Senior API Design, Architecture, Scalability & Production Scenarios Senior Advanced

Quick Interview Answer

The Outbox pattern helps reliably coordinate a database state change with publication of an integration message. The application writes both the business change and an outbox record in the same local database transaction.

Detailed Explanation

A background publisher later sends unsent outbox messages and marks them processed. Consumers should still be idempotent because message delivery can occur more than once.

Code Example

await using var tx = await db.Database.BeginTransactionAsync(token);

db.Orders.Add(order);
db.OutboxMessages.Add(new OutboxMessage(eventJson));

await db.SaveChangesAsync(token);
await tx.CommitAsync(token);

// Background worker publishes the outbox message.