Why would you use a message based system?

Question

What are the motivations for using a message based system?

I'm seeing a lot about service buses such as NServiceBus and Mass Transit and I'm wondering what the benefits of the underlying methodology are.

Answer 1

There are multiple advantages to using message based systems.

1. Messages form a well defined technology neutral interface between applications.
2. Enables loose coupling of applications.
3. Lots of options for performance, tuning and scaling:
   • Deploy requester and service process on different hardware
   • Multiple requesters sharing single server
   • Multiple requesters sharing multiple servers
4. The various messaging middlewares implement the common messaging patterns independently from you application.
   • Request/Reply
   • Fire and Forget offline updates
   • Publish/Subscribe
5. Many of the middleware products handle message transformation (e.g. SWIFT to SWIFTXML).
6. Many of the middleware products can decompose a single large request into several smaller requests.
7. They nearly all support multiple platforms.

Incidentally the two market leaders in this area are IBM with their Websphere MQ and related products, and, TIBCO with their Enterprise Service Bus.

Answer 2

A message-based architecture de-couples producers and consumers of messages, both in time and space. This has a lot of benefits:

• producers and consumers can run on different machines
• producers and consumers can run at different times.
• producers and consumers can run on different hardware/software platforms (they only need to understand the same message protocol)
• it's easy to coordinate multiple producers / consumers (e.g. for compute-intensive jobs that need multiple machines, as Dave Markle has described)
• higher stability when services are temporarily unavailble (e.g. when doing order processing, using a messaging system can help avoid "dropping" orders)

You lose most of these benefits when you do RPC-style communication (i.e. when you block while waiting for service responses)