Event-Driven Architecture with MassTransit
Build event-driven microservices with MassTransit — message consumers, sagas, request-response, and integration with RabbitMQ and Azure Service Bus.
50 min•By Priygop Team•Last updated: Feb 2026
MassTransit Fundamentals
- Abstraction: MassTransit abstracts message broker details — switch between RabbitMQ, Azure Service Bus, and Kafka without changing business logic
- Consumers: Classes that handle messages — each consumer processes one message type. Automatic retry, error handling, and dead-letter queuing
- Publish-Subscribe: Publish events (OrderCreated) — all interested consumers receive a copy. Loose coupling between publishers and subscribers
- Request-Response: Synchronous request over message broker — client sends request, waits for response. Used when synchronous pattern is needed
- Saga State Machine: Manage long-running processes — Automatonymous state machines track order fulfillment across multiple services with compensation
- Outbox: Transactional outbox pattern — ensures messages are only sent when database transaction commits. Prevents message loss and double-publishing
Event-Driven Patterns
- Domain Events: Notify other services about business events — OrderPlaced, PaymentProcessed, ShipmentDispatched. Published via MassTransit or MediatR
- Integration Events: Events crossing service boundaries — include all data the consumer needs (not just IDs) to avoid synchronous callbacks
- Idempotent Consumers: Messages may be delivered more than once — consumers must produce the same result regardless. Use InMemoryOutbox or message deduplication
- Dead Letter Queue: Messages that fail after max retries go to DLQ — monitor DLQ size, investigate and reprocess failed messages
- Event Versioning: Add new fields with defaults, never remove existing fields — backward compatibility allows independent service deployment
- Monitoring: Track message throughput, consumer lag, retry rates, DLQ size — Prometheus metrics built into MassTransit