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Messaging Patterns

Messaging Patterns. An alternative approach to modeling with ESB’s. Jimmy P @ pjimmy mail@thejimmyp.com http:// www.blog.thejimmyp.com. Outline. Some Context Some Problems Intro to Messaging Systems Some Solutions And The Focus Some Patterns. Platform. Temporal. Spatial. Afferent.

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Messaging Patterns

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  1. Messaging Patterns An alternative approach to modeling with ESB’s Jimmy P @pjimmy mail@thejimmyp.com http://www.blog.thejimmyp.com

  2. Outline • Some Context • Some Problems • Intro to Messaging Systems • Some Solutions • And The Focus • Some Patterns

  3. Platform Temporal Spatial Afferent Efferent It’s mainly about coupling

  4. Platform Temporal Spatial Afferent Efferent AKA interoperability Most RPC and other common messaging technologies are platform dependent in painful places

  5. Platform Temporal Spatial Afferent Efferent When A calls B synchronously B’s processing time affects A A B A Calls B A Blocks While B Processes B Processes B Returns

  6. Platform Temporal Spatial Afferent Efferent Where are the components physically? Is there multiple instances, and where are they? How do I decide which of multiple logically identical components I should send my message to? What happens if the only physical instance I know of is down?

  7. Platform Temporal Spatial Afferent Efferent Afferent - What do I take a dependency on? Efferent - What takes a dependency on me?

  8. But it’s also a little about data loss

  9. When Servers Crash DB App Tx [HTTP] $$ Order Call 1 of 3 Call 2 of 3 Critical Windows Patch Rollback Where’s the order!?

  10. When Databases Are Down DB App Tx Exception Down Write to log [HTTP] $$ Order Call 1 of 3 Where’s the order!?

  11. When Deadlocks Happen DB App Tx Exception A B Write to log [HTTP] $$ Order Call 1 of 3 Call 2 of 3 Deadlock Where’s the order!?

  12. Data Loss Using Web Services A B C D $$ Order Not Rolled back [HTTP] Invoke DB WS Rollback Deadlock

  13. So What is SOA and what are messaging systems?

  14. Bus vs. Brokervs. RPC Broker .NET WCF Service JAVA WEB Service External JSON Service SalesForce SVC A SVC B SVC C SAP BUS BUS BUS Service A Service C Service B Service D Service E Service C Service F

  15. What makes up a messaging system • Messages travel between queues • Queues are persistent stores located on the machine the service is deployed to • Queues can persist messages to non volatile storage in case of faults • Adding and removing messages from queues can be transactional • Queues provide us with our asynchronous behavior

  16. So How does messaging help with coupling?

  17. Platform Temporal Spatial Afferent Efferent XML for message format & XSD for message schema Communication protocol and addressing is a problem

  18. Platform Temporal Spatial Afferent Efferent Asynchronous messaging

  19. Platform Temporal Spatial Afferent Efferent Create logically autonomous services Address services logically not physically

  20. Platform Temporal Spatial Afferent Efferent Use the message schema to create a level of indirection between services so there is no direct dependency Schema A Schema B Service A Service B Communications Infrastructure

  21. And with data loss?

  22. Messages are transactions Tx Q Receive App DB $$ Order Call 1 of 3 Call 2 of 3 Rollback Rollback The order is back in the queue

  23. Web Services with Messaging The message won’t be sent if there’s a failure A B C D $$ Order Msg [HTTP] Invoke DB Messaging Gateway WS

  24. So messaging is the silver bullet ;)Let’s look at some patterns

  25. Return Address Pattern • Provides a place to specify a physical address per message, allowing of logical addressing per message type • Now EndpointA can do other work while waiting for it’s response

  26. Load Balancing with Return Address • EndpointA can specify an endpoint under less load to process the response if it has that information

  27. Correlated Request/Response • An extension of Return Address • Allows services to maintain state

  28. Multiple Responses with Correlated Request/Response • User may not know or care about ALL of the responses

  29. Multiple Handlers with Correlated Request/Response • Ultimate in SRP

  30. Publish/Subscribe • Allows us to add Events to our modeling arsenal • By subscribing to message types from a logical address we are only coupled to schema • This allows us to trivially increase parallelism as required

  31. Modeling Business with Messaging Systems • Simpler more Robust systems

  32. Resources and Thanks • http://www.nservicebus.com/ • service-orientated-architecture@yahoogroups.com • nservicebus@yahoogroups.com • dddcqrs+noreply@googlegroups.com • If you are really keen watch this space http://www.udidahan.com/training/ a truly life changing course • And many thanks to Udi for letting me steal his pretty animated slides and a diagram here and there. Made me look better than I deserved and saved me heaps of work

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