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Ride The Bus!
- 1. d60 developing smart software solutions Ride the bus! April 2012
- 2. Mogens Heller Grabe mhg@d60.dk @mookid8000 h8p://mookid.dk/oncode
- 3. Agenda • What is messaging • Doing it with NServiceBus • Enter the saga
- 4. What is messaging? void CreatePresentation(string name); -‐-‐ someObject.CreatePresentation(“Ride The Bus!”);
- 5. What is messaging? • Networks are unreliable • Inter-‐process communicaKon is dead slow • The other process might not be there at the moment • etc • etc
- 6. What is messaging? void CreatePresentation(CreatePresentationArgs args); -‐-‐ var args = new CreatePresentationArgs { Title = “Ride The Bus!” }; someObject.CreatePresentation(args);
- 7. What is messaging? void Process(Args args); -‐-‐ someObject.Process(new CreatePresentation { Title = “Ride The Bus!” }); someObject.Process(new Something()); someObject.Process(new SomethingElse());
- 8. What is messaging? void
- 9. InteresKng properKes • Can be persisted • Can be forwarded • etc
- 10. Persisted?
- 11. MSMQ can do that! • Ships with all modern versions of Windows • Your MSMQ endpoint is always local – remoKng is taken care of via outgoing queues • .NET client in System.Messaging (GAC).
- 12. Bus?
- 15. • Each service has its own input queue. • When a service needs to send a message, the bus looks up the desKnaKon somehow. • How desKnaKons are looked up depends on whether the service is sending or publishing.
- 18. “Request/reply” + “Return address” + maybe “CorrelaKon idenKfier”
- 23. “Process manager” + “CorrelaKon idenKfier”
- 24. How to do these things IRL • Commercial – NServiceBus • Free alternaKves – MassTransit – RhinoESB – Rebus(*)
- 25. NServiceBus • Currently in version 3.0 • Licensing – <= 2.0 are free – >= 2.5 cost money
- 26. Show me the code • Now let’s see how “Request/reply” looks with NServiceBus – We have a pre8y unreliable web service, umm “Whatchamacallit”, that we want to call. – We build an integraKon service with NServiceBus that works as a messaging façade towards the web service. – Our system requests stuff from the façade, the façade replies.
- 27. Show me the code • Now, let’s see an example with some Pub/sub acKon – We have a service that processes something, “Somekindofprocessor”, when it receives a ProcessSomething command. – In order to process stuff, it needs to get the important string from our unreliable web service from before. – When processing is done, it should publish the result, allowing any other interested services to react to this.
- 30. The real world is a place... • ...where we can’t always process messages in a stateless manner like this... • ...where mulKple things need coordinaKon and will not always succeed/fail as a whole...
- 31. Enter the saga! • A model for long-‐lived transacKons. • “A long-‐lived transacKon is a saga if it can be wri8en as a sequence of transacKons that can be interleaved with other transacKons.” • For some reason, Mike Amundsen keeps a copy of the original whitepaper PDF here: h8p://www.amundsen.com/downloads/sagas.pdf
- 32. Sagas • Implemented with an implementaKon of ISagaEntity, TEntity and deriving a message handler from Saga<TEntity>. • All handled messages should somehow be correlated with the sata data.
- 33. Show me the code • Just do it
- 34. Sagas • Use them to – implement short conversaKons – implement long conversaKons – handle Kmeouts – implement idempotency
- 35. Thanks for listening! mhg@d60.dk @mookid8000 h8p://mookid.dk/oncode
- 36. Image credits “It’s the same mouth, just flipped”: h8p://humor-‐image.com/its-‐the-‐same-‐mouth-‐just-‐flipped/ Thanks for lepng me borrow your awesome images – if you ever meet me, I’ll buy you guys and girls a beer. Seriously, I will.