MassTransit

MassTransit is an open-source .NET framework for building message-based distributed applications. It provides a consistent programming model for sending and receiving messages and supports common integration patterns such as publish/subscribe, request/response, and long-running workflows via sagas. The library is designed to run on the .NET platform and integrates with popular ASP.NET Core applications and other .NET services.

At runtime, MassTransit centers on a bus that connects to a transport (such as RabbitMQ, Azure Service Bus, Amazon SQS, or ActiveMQ). Receive endpoints host consumers that implement business logic in response to specific message types. Sagas implement long-running workflows with state, coordination, and compensating actions. The framework offers a middleware pipeline, dependency injection integration, and tooling for testing and instrumentation.

Key features include support for multiple transports through a pluggable architecture, message retries and fault handling, scheduling and delayed delivery, message correlation, and an in-memory test harness for unit tests. MassTransit also provides support for sagas and state machines, enabling complex orchestration patterns while keeping services loosely coupled.

MassTransit originated as an open-source project in the .NET ecosystem and has grown through community contributions. It is licensed under the Apache 2.0 license and is hosted on GitHub. It is widely used for building microservices and event-driven architectures that rely on a message broker to decouple components and improve scalability and reliability.