Building reliable, scalable, maintainable distributed applications is next to impossible without the right tools. NServiceBus is an open-source .NET framework that will help you to do just that. This code-focused presentation covers the fundamentals of NServiceBus development, including one-way messaging, publish and subscribe, and implementing long-running business processes. In the code example, we start with fairly simple code for a user to create an account on a website and expand it to include an email verification feature using NServiceBus. In the first phase, we’ll move the work of creating the user into the service layer, so that we can get an example of how NServiceBus works at its most fundamental level. In the second phase, we will up the ante significantly, using a Saga (a long running business process) to implement an email verification check. This includes sending an email with a verification code to the user, and then verifying that code before finally creating the user.

1. Distributed Application Development with NServiceBus David Boike www.make-awesome.com @DavidBoike Presentation and source: http://bit.ly/fOn4U9

2. Real-Life Example using (TransactionScopets = newTransactionScope()) { InsertOrUpdateAlertPreferences(); UpdateAlertEmails(); InternalWebService.UpdateEmailSettings(listID, emailAddresses); ts.Complete(); }

3. Real-Life Example – It Gets Worse using (TransactionScopets = newTransactionScope()) { InsertOrUpdateAlertPreferences(); UpdateAlertEmails(); InternalWebService.UpdateEmailSettings(listID, emailAddresses); ExternalWebService.UpdateSmsSettings(keyword, phoneNumber); ts.Complete(); }

4. NServiceBus to the rescue! Enterprise Service Bus for .NET Not a centralized broker like BizTalk Not a services communication framework like WCF Created by UdiDahan, internationally renowned expert on software architecture and design Focuses on messaging and publish/subscribe Ultra reliable Provides friction against poor architecture decisions

5. How it Works Utilizes assembly scanning for component discovery Uses marker interfaces to identify message schemas, message handlers, configuration sources, etc. Uses dependency injection (inversion of control) to detect and provide dependencies and services Everything is pluggable

6. App How an Endpoint Works MSMQ Transactional Receive

7. Transaction App How an Endpoint Works MSMQ Transactional Receive

8. Transaction How an Endpoint Works Perform database operations within the distributed transaction MSMQ DB App

9. Transaction How an Endpoint Works Or connect to a traditional web service MSMQ App Web Service

10. Transaction App How an Endpoint Works Send or publish additional messages MSMQ

11. Transaction Transient Errors If an exception happens, the transaction rolls back and returns the message to the queue. Transaction Rolling Back MSMQ Automatic retries are an integral part of the system. Exception App

12. Poison Messages After a configurable number of retries, poison messages get sent to an error queue. Transaction Rolling Back MSMQ Fix the underlying issue, and you can return error messages to their source queue. App Error

13. Real-Life Example - Revisited Webapp Bus.Send(new SaveAlertsCmd()); Alert Service Bus.Publish(new AlertsUpdatedEvent()); Subscriptions Bus.Subscribe<AlertsUpdatedEvent>(); Web Svc Adapter SMS Adapter

14. Getting Started Go to http://www.nservicebus.com Click the Download link Follow the instructions Be sure to run RunMeFirst.bat fromthe command prompt with admin rights! Installs and/or verifies MSMQ configuration Sets the appropriate settings on the Microsoft Distributed Transaction Coordinator Installs performance counters Run from the command prompt so you can see if there are any errors.

15. Let’s Build Something

16. In case you missed it… If you are watching the presentation live, the next several slides are apt to be very boring. Sorry. For those of you at home, this is what we did so you can follow along in the code samples.

17. Code Phase 1: Messaging Create MyMessages assembly Add reference to NServiceBus.dll Add CreateUserCmd

18. Code Phase 1: Messaging Create UserService assembly Add reference to NServiceBus.dll, NServiceBus.Core.dll, NServiceBus.Host.exe, and Log4Net Add IConfigureThisEndpoint, AsA_Publisher Add UserCreatorservice implementing IHandleMessages<CreateUserCmd> Add Start Action to run NServiceBus.Host.exe

19. Code Phase 1: Messaging Modify web project Add Global.asax, providing a global home for the web application’s IBus instance Modify Web.config with NServiceBus configuration Modify Register.aspx.cs to send the message

20. Code Phase 2: Saga/Verification CreateUserSagaData : ISagaEntity Copy properties from CreateUserCmd Add VerificationString property Change from service handling CreateUserCmd to saga started by CreateUserCmd Set saga data from command Override ConfigureHowToFindSaga, calling ConfigureMapping<CreateUserCmd>() method

21. Code Phase 2: Saga/Verification “Send” verification email Create SendVerificationEmailCmd Create mock handler that logs verification code to console Configure UserCreatorApp.config to send to the UserService (itself, although this could be a separate project) Send SendVerificationEmailCmd from the Handle<CreateUserCmd> method

22. Code Phase 2: Saga/Verification Verify the email Create VerifyEmailCmd in MyMessages Create UserCreatedEvent in MyMessages Add IHandle<VerifyEmailCmd> to saga and configure how to find saga data from this command Add implementation, actually creating user in DB MarkAsComplete(), log, and Bus.Return(0)

23. Code Phase 2: Saga/Verification Web handler for email link Create Verify.aspx Configure Web.config to send VerifyEmailCmd to UserService Change Register.aspx.cs redirect from Login to Verify

24. All caught up!

25. Where to learn more NServiceBus website: www.nservicebus.com My blog: www.make-awesome.com Ask on Stack Overflow (tag with “nservicebus”) Udi’sblog: www.udidahan.com Andreas Ohlund’sblog: www.andreasohlund.net Jonathan Oliver’s blog: www.jonathanoliver.com Twitter: #NServiceBus Presentation Source Code: http://bit.ly/fOn4U9