NSERVICEBUS

Inspired by: The course authored by Udi Dahan

Oslo/Fagdag

Espen Ekvang/Tomas Jansson

01/03/2013

2AGENDA

• Intro

• Messaging and queues

• Testing

• SOA

• Saga

4INTRO

• Fallacies of distributed computing

• Why NServiceBus?

• Bus vs. Broker

• Service orientation

• Excercises

5FALLACIES OF DISTRIBUTED COMPUTING

1. The network is reliable

2. Latency isn’t a problem

3. Bandwidth isn’t a problem

4. The network is secure

5. The topology won’t change

6. The administrator will know what to do

7. Transport cost isn’t a problem

8. The network is homogeneous

Cant’ assume WHEN the message will arrive,

IF AT ALL

6WHY NSERVICEBUS

1. The network is reliable

2. Latency isn’t a problem

3. Bandwidth isn’t a problem

4. The network is secure

5. The topology won’t change

6. The administrator will know what to do

7. Transport cost isn’t a problem

8. The network is homogeneous

NServiceBus addresses the first five directly

The most developer-friendly service bus for SOA on .NET

7BUS VS. BROKER

Buss.dll

App

Buss.dll

AppBuss.

dll

App

App

App App

Broker

• Bus is not necessarily physically separate• Simpler; no routing or service fail over• No single point of failure

8TENETS OF SERVICE ORIENTATION• Services are autonomous• Share contract & schema, not class or

type• Boundaries are explicit• Compatibitility is base on Policy

9LAYERS & COUPLING

UI

BL

DAL

DB

SalesShippin

gCRM

Tight coupling

Loose coupling

Referential Integrity

Reintroduces coupling

10WHEN CAN I WRITE SOME CODE?

• Getting started• New class library

• Install-Package NServiceBus.Host

• Logging• NServiceBus uses log4net, you can configure logging in app.config

• Default output is console

11EXERCISES

HELLO WORLD

LOGGING

12MESSAGING AND QUEUES

• Store & forward

• Dangers of store & forward

• Request/Response

• Messaging and NServiceBus

• Exercises

13

SERVER

STORE & FORWARD

MSMQ

OUTGOING INCOMING

CLIENT

MSMQ

OUTGOING INCOMING

Store & Forward writes to disk

Resilient in the face of failures

14DANGERS OF STORE & FORWARD

• If target is offline for an extended period of timemessages can fill up the disk• Can cause a server to crash

• Especially problematic in B2B integration• 1 MB/message, 100 message/sec = 6GB/minute

• Solution – discard messages after a while• Use [TimeToBeReceived("00:01:00")] on the message definition

15REQUEST/RESPONSE

SERVER

MSMQ

OUTGOING INCOMING

CLIENT

MSMQ

OUTGOING INCOMING

Client can’t assume when a response will arrive, if at all

Equivalent to 2 one-way messages

16REQUEST/RESPONSE

• Message is sent from the server to the client’s queueIf the client is offline, message sits in the server machine’s outgoing queue

• Client is not blocked until response arrives

• If two requests were sent, responses may arrive out of order

17WARNING! THIS IS NOT RPC

• Do NOT try to implement regular request/response patterns on top of messaging

• The client should be designed so that it can continue operating if a response never comes

Differences from RPC

• RPC is easy to code• After invoking a web service• Next line of code assumes we’ve got a response

• RPC problems• Can’t reason about the time between one line of code and another

• Messaging makes this all explicit

18MESSAGING AND NSERVICEBUS

SERVER

MSMQ

OUTGOING INCOMING

CLIENT

MSMQ

OUTGOING INCOMING

Transaction

19DEFINE A MESSAGE

• Preferably inherit from IEvent or ICommand

• Use IMessage when replying using Bus.Reply()

• Also possible to define your own convention• Configure.DefiningMessagesAs(t=>MyOwnConvention(t))

• Add properties like a regular class/interface

• Keep contract definintions in their own assembly/project

public class MyEvent: IEvent {}

20INSTANTIATE A MESSAGE

• var myMessage = new MyMessage();

• var myMessage = Bus.CreateInstance<MyMessage>();

21SEND A MESSAGE

Bus.Send(messageObject);

Can instantiate and send together (useful for interfaces):

Bus.Send<IMessage>((message) =>

{

message.Prop1 = value1;

message.Prop2 = value2;

});

22SPECIFY DESTINATION

1. Bus.Send(destination, messages);

Requires that application manages routing

2. Configure destination for message type.

In <UnicastBusConfig>, under <MessageEndpointMappings> specify one of the following:

- <add Messages="assembly" Endpoint="destination"/>- <add Messages="type" Endpoint="destination"/>

3. Specify destination using

- QueueName@ServerName , or

- Just QueueName for the same machine

23HANDLE A MESSAGE

Write a class that implements IHandleMessages<T> where T is a message type

public class MyHandler : IHandleMessages<MyMessage>

{

public void Handle(MyMessage message)

{

}

}

Remember to specify in <UnicastBusConfig>, under

<MessageEndpointMappings> one of the following:

- <add Messages="assembly" Endpoint="source"/>- <add Messages="type" Endpoint="source"/>

24CONFIGURING AN ENDPOINT

When configuring an endpoint inherit from

1. Using AsA_Client will

- use non-transactional MsmqTransport- purge its queue of messages on startup- processes messages using its own permissions, not those of the message sender

2. Using AsA_Server will

- use transactional MsmqTransport- not purge its queue of messages on startup, hence fault-tolerant- processes messages using the permissions of the sender (impersonation)

3. Using AsA_Publisher will

- extends AsA_Server - indicates to the infrastructure that a storage for subscription request is to be set up

25EXERCISES

ONE-WAY MESSAGING (CLIENT)

PROCESSING MESSAGES (SERVER)

EXCEPTIONS

26UNIT TESTING MESSAGE HANDLERS

Available from NuGet using

Install-Package NServiceBus.Testing

Provides the ability to set expectations around how message handlers handle messages

• Expect: Send, Reply, Publish, etc...

Test.Initialize();

Test.Handler<MyHandler>()

.ExpectPublish<MyMessage>(message => message.Prop1 == value1)

.OnMessage<SomeEvent>(someEvent =>

{

someEvent.Prop1 = inputValue1;

});

27EXERCISE

UNIT TESTING

28SAGA

• Definition

• Saga declaration

• Saga ending

• Saga testing

• Exercise

29SAGA - DEFINITION

A Saga:

• Is a pattern for implementing long-lived transaction by using a series of shorter transactions

• Holds relevant state to needed to process mulitple messages in a ”saga entity”

• Are initiated by a message (event/command)

30SAGA - DECLARATION

public class MyPolicy : Saga<MyPolicyData>,

IAmStartedByMessages<MyMessage1>,

IHandleMessages<MyMessage2>

{

public void Handle(MyMessage1 order)

public void Handle(MyMessage2 order)

}

• Methods are like regular message handling logic• Sagas can be started by multiple messages

(IAmStartedByMessages<T>)• First messages should start saga, following messages should be

processed by the same one

31SAGA – DECLARATION CONT.

public class MyPolicyData : ISagaEntity

{

public Guid Id { get; set; }

public string Originator { get; set; }

public string OriginalMessageId { get; set; }

}

32ENDING A SAGA

MarkAsComplete();

• Can call this from any method

• Causes the saga to be deleted

• Any data that you want retained should be sent on (or published) via a message

33UNIT TESTING A SAGA

Test.Saga<MyPolicy>()

.ExpectPublish<Message1>(/* check values */)

.ExpectSend<Message2>(/* check values */)

.ExpectReplyToOriginator<Message3>(/* check values */)

.When(saga => saga.Handle(myMessage));

/* check values */

message => return(message.Data == someValue);

34EXERCISE - SAGAS ROCK

35EXTRA EXERCISES

TIMEOUTCUSTOM XML NAMESPACECONFIGURABLE ROUTINGDEPENDENCY INJECTIONWEB-APP HOSTINGFULL DUPLEXDISTRIBUTION GROUP EXERCISE