nsb-skillsmatter-20081127

8/3/2019 nsb-skillsmatter-20081127

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Asynchronous .NETapplications with

NServiceBus

David de Florinier ([email protected])

Gojko Adzic ([email protected])

Skills Matter 27/11/2008


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Don't be afraid of messaging


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http://www.sxc.hu/photo/1084274

Fire and forget...


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Fire and forget

Use when the second part of a process has to becompleted, but we don't really have to wait for itto finish. This typically involves an external

system or batch processing.

Resilience

Easier to test Option to go offline


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Just leave it there when you're done



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Just leave it there when you're done

Use when the second part of a process is slow ortalks to an external system, but completing thetask is important to continue the work.

Better UI responsiveness

Performance

Better resource usage


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Share the load

http://www.flickr.com/photos/library_of_congress/2179123671/


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Share the load

Use when lots of different agents can submit orprocess work. Decouple workers andrequesters.

Performance

Scalability

More flexible

Easier to extend


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The key to efficient asyncarchitectures!


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Who? ... What? ...Where?

Written by Udi Dahan

It is an open source communications framework

Get it from http://www.nservicebus.com

Released under the Apache Licence 2.0

Current Release is 1.8


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Getting Started

Download fromhttp://www.nservicebus.com/Downloads.aspx

Extract the files from the zip, then build using

build.bat (this uses msbuild) The assemblies will now be in the build folder

(and subfolders)

Look through the Sample projects, these coverall the simple usage cases (for Spring)


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What is included...


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IBuilder

Various parts of the framework (e.g. passingmessages to handlers) use a service locatorpattern.

This is done using the IBuilder interface An implementation using Spring is provided:

ObjectBuilder.SpringFramework

An exampleof a implementation for CastleWindsor is in the Demo source


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ITransport

Responsibility for sending and receivingmessages is delegated to a transportcomponent

Unicast Implementations for MSMQ and Httpare provided

There is an IMulticastTransport interface, butthere are no implementations provided


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IMessageSerializer

Responsibilty for serialization of messages isdelegated to a serialization component

Implementations for Binary and Xml

serialization are provided Has the following methods

void Initialize(params Type[] types);

void Serialize(IMessage[] messages, Stream stream);

IMessage[] Deserialize(Stream stream);


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IBus

The entry point for your code

Send, Subscribe, Unsubscribe, Publish

IUnicastBus and IMulticastBus interfaces inherit

from IBus,

Use IUnicastBus with IUnicastTransport

Use IMulticastBus IMulticastTransport


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Publish/Subscribe

Messages should implement theIMessage marker interface

Use IBus.Publish(IMessage)

Use IBus.Subscribe(Type[,predicate])

Message handlers implementIMessageHandler

Implement IBuilder interface to createan handler builder if not using

Spring.Net


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ISubscriptionStorage

Needs to be configured for publishers

Persistence and retrieval of subscriptions isdelegated to ISubscriptionStorage

Db and Msmq implementations are provided

Db implementation allows multiple publisherinstances to share one subscription store


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Publish/Subscribe config Always needed

Transport : NumberOfWorkerThreads, IsTransactional, InputQueue

Bus: ITransport, IMessageSerializer.

On Publisher:

SubscriptionStorage : persistence for subscriptions

Bus: ISubscriptionStorage

On Subscriber

Transport : NumberOfWorkerThreads, IsTransactional, InputQueue

no need for ISubscriptionStorage.

IBuilder must be able to build Handlers

Bus: MessageOwners: where subscription messages are sent

Bus: AddTypesFromAssembly for handler types


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Publish Subscribe demo


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Full Duplex

Use IBus.Send(IMessage).Register(Callback) to makeasynchronous request

Use IBus.Reply(Response) to send response


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Full Duplex code

Sending message from the client

bus.Send(["worker@localhost", ]msg).Register(callback, msg);

Handling the message on the server

_bus.Reply(response);

Handling the callback on the clientprivate void callback(IAsyncResult ar) {

....

CompletionResult result = asyncResult.AsyncState as CompletionResult;

Message request = result.State as Message;

...

foreach (var message in result.Messages) { ...}

....

}


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Full Duplex demo


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Saga

Framework for long lived message workflows

Saga Messages implement ISagaMessage

Implement ISaga to handle saga messages

NserviceBus.Testing.Saga contains Mock objects for use

in unit tests


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ISagaPersister

The responsibility of persisting and rehydratingSaga entities is delegated to a classimplementing ISagaPersister

DbBlobSagaPersister implementation provided


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ISaga

Saga Enitity, which will handle the various stepsin the saga workflow, will implement ISagafor each workflow step

Also a class extending SagaMessageHandlermay be used. This will typically override theHandle and NeedToHandle methods.

The SagaMessageHandler uses ISagaPersister

to rehydrate the ISaga implementation, andcall it's Handle method


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Saga interaction


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Saga Demo


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Distributor

A way of scaling costlytransactions

Workers report for work

Distributor sends work tofirst available worker

When workers have

completed, they report forwork again

An executable is provided


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Conclusions

Positives Source code is well structured and easy to

understand

Main objects can be extended, flexible architecture

Has performed well in load tests

Few dependencies

Negatives

There is little documentation


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Some alternatives?

ActiveMQ and NMS

http://activemq.apache.org/nms.html

SimpleServiceBus

http://www.codeplex.com/SimpleServiceBus

MassTransithttp://code.google.com/p/masstransit/


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Links

http://www.nservicebus.com

http://www.udidahan.com

http://ayende.com/Blog/archive/2008/03/24/NSe

rviceBus-Review.aspx

http://gojko.net


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Next events

TDD in .NET, 17/Dec

OpenSource .NET Exchange 22/Jan

Fitnesse.NET tips and tricks, 17/Feb

For more info: http://ukdotnet.ning.com/


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Questions?

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