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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.
Citation preview
Distributed Application Development with NServiceBus
David Boikewww.make-awesome.com
@DavidBoike
Presentation and source: http://bit.ly/fOn4U9
Real-Life Exampleusing (TransactionScope ts = new TransactionScope()){
InsertOrUpdateAlertPreferences();UpdateAlertEmails();
InternalWebService.UpdateEmailSettings(listID, emailAddresses);
ts.Complete();}
Real-Life Example – It Gets Worseusing (TransactionScope ts = new TransactionScope()){
InsertOrUpdateAlertPreferences();UpdateAlertEmails();
InternalWebService.UpdateEmailSettings(listID, emailAddresses);
ExternalWebService.UpdateSmsSettings(keyword, phoneNumber);
ts.Complete();}
NServiceBus to the rescue!Enterprise Service Bus for .NET
Not a centralized broker like BizTalkNot a services communication framework like
WCFCreated by Udi Dahan, internationally
renowned expert on software architecture and design
Focuses on messaging and publish/subscribeUltra reliableProvides friction against poor architecture
decisions
How it WorksUtilizes assembly scanning for component
discoveryUses 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
App
How an Endpoint Works
MSMQ
TransactionalReceive
Transaction
App
How an Endpoint Works
MSMQ
TransactionalReceive
Transaction
App
How an Endpoint Works
MSMQ
DB
Perform database operations within the distributed transaction
Transaction
App
How an Endpoint Works
MSMQ
Web Service
Or connect to a traditional web service
Transaction
App
How an Endpoint Works
MSMQ Send or publish additional messages
Transaction
Transient ErrorsIf an exception happens, the transaction rolls back and returns the message to the queue.
TransactionRolling Back
ExceptionApp
MSMQ
Automatic retries are an integral part of the system.
TransactionRolling Back
Poison MessagesAfter a configurable number of retries, poison messages get sent to an error queue.
App
MSMQ
Error
Fix the underlying issue, and you can return error messages to their source queue.
Real-Life Example - RevisitedWebapp Bus.Send(new
SaveAlertsCmd());
AlertService
Bus.Publish(new AlertsUpdatedEvent());
SMS Adapter
Web Svc Adapter
Bus.Subscribe<AlertsUpdatedEvent>();
Subscriptions
Getting StartedGo to http://www.nservicebus.comClick the Download linkFollow the instructionsBe sure to run RunMeFirst.bat from the
command prompt with admin rights!Installs and/or verifies MSMQ configurationSets the appropriate settings on the Microsoft
Distributed Transaction CoordinatorInstalls performance counters
Run from the command prompt so you can see if there are any errors.
Let’s Build Something
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.
Code Phase 1: MessagingCreate MyMessages assembly
Add reference to NServiceBus.dllAdd CreateUserCmd
Code Phase 1: MessagingCreate UserService assembly
Add reference to NServiceBus.dll, NServiceBus.Core.dll, NServiceBus.Host.exe, and Log4Net
Add IConfigureThisEndpoint, AsA_PublisherAdd UserCreator service implementing
IHandleMessages<CreateUserCmd>Add Start Action to run NServiceBus.Host.exe
Code Phase 1: MessagingModify 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
Code Phase 2: Saga/VerificationCreateUserSagaData : ISagaEntity
Copy properties from CreateUserCmdAdd VerificationString property
Change from service handling CreateUserCmd to saga started by CreateUserCmdSet saga data from commandOverride ConfigureHowToFindSaga, calling
ConfigureMapping<CreateUserCmd>() method
Code Phase 2: Saga/Verification“Send” verification email
Create SendVerificationEmailCmdCreate mock handler that logs verification code
to consoleConfigure UserCreator App.config to send to
the UserService (itself, although this could be a separate project)
Send SendVerificationEmailCmd from the Handle<CreateUserCmd> method
Code Phase 2: Saga/VerificationVerify the email
Create VerifyEmailCmd in MyMessagesCreate UserCreatedEvent in MyMessagesAdd 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)
Code Phase 2: Saga/VerificationWeb handler for email link
Create Verify.aspxConfigure Web.config to send VerifyEmailCmd
to UserServiceChange Register.aspx.cs redirect from Login to
Verify
All caught up!
Where to learn moreNServiceBus website: www.nservicebus.comMy blog: www.make-awesome.comAsk on Stack Overflow (tag with
“nservicebus”)Udi’s blog: www.udidahan.comAndreas Ohlund’s blog:
www.andreasohlund.netJonathan Oliver’s blog:
www.jonathanoliver.comTwitter: #NServiceBusPresentation Source Code: http://
bit.ly/fOn4U9
