Building enterprise
applications with
NServiceBus
Andreas Öhlund
onsdag den 12 maj 2010

What is a distributed
system?
“A distributed system is one in which the
failure of a computer you didn't even
know existed can render your own
computer unusable”
-Leslie Lamport
onsdag den 12 maj 2010

The first rule of NServiceBus
onsdag den 12 maj 2010

There is NO Service Bus!
The first rule of NServiceBus
onsdag den 12 maj 2010

Well, at least no physical one
onsdag den 12 maj 2010

The second rule of NServiceBus
onsdag den 12 maj 2010

You DO NOT use
synchronous communication
The second rule of NServiceBus
onsdag den 12 maj 2010

The key to robust communication
onsdag den 12 maj 2010

Store and forward
onsdag den 12 maj 2010

Request/Response the
NServiceBus way
Fire and forget X 2
onsdag den 12 maj 2010

The effect of
tight coupling
Temporal
Behavioral
onsdag den 12 maj 2010

Communication and coupling
onsdag den 12 maj 2010

Coupling NServiceBus style
onsdag den 12 maj 2010

Command oriented
communication
CompleteSaleCommand
OnlineSales OrderService
onsdag den 12 maj 2010

Sending Messages
IBus.Send()
bus.Send(new CompleteSaleCommand
CreateOrderCommand
{
ProductId = 123,
OnlineSales
Quantity = 10
....
});
onsdag den 12 maj 2010

Receiving and
processing of messages
public class CompleteSaleMessageHandler:
CreateOrderCommand
IHandleMessages<CompleteSaleCommand>
{ OrderService
public void Handle(CompleteSaleCommand c)
{
...
}
}
onsdag den 12 maj 2010

Message Contracts
• Versioned by the owner
• Regular .Net Assembly
• Bound to a input queue
• class MyMessage :
IMessage
onsdag den 12 maj 2010

Throttling the load
• Manage traffic peaks
• Consumer controls the pace
• <MsmqTransportConfig
NumberOfWorkerThreads="3" />
onsdag den 12 maj 2010

What happens when the load
becomes to heavy for one server?
onsdag den 12 maj 2010

Scaling with the Distributor
onsdag den 12 maj 2010

Building consistent systems
• Do we produce
predictable results even
under failure conditions?
• What about non
transactional sources?
onsdag den 12 maj 2010

Isolate non transactional sources as
separate endpoints
public void Handle(CompleteSaleCommand cmd)
{
var order = ....
orderRepository.Save(order)
smtpClient.Send(new MailMessage{...})
}
onsdag den 12 maj 2010

Isolate non transactional sources as
separate endpoints
public void Handle(CompleteSaleCommand cmd)
{
public void Handle(CompleteSaleCommand cmd)
{ var order = ....
orderRepository.Save(order)
var order = ....
orderRepository.Save(order)
bus.Send(new NotifyCustomerRequest
{
smtpClient.Send(new MailMessage{...})
} EmailAddress = customer.Email,
Body = “Order confirmation”
});
}
onsdag den 12 maj 2010

Idempotent
“Idempotent operations are operations that can be applied
multiple times without changing the result”
onsdag den 12 maj 2010

When things go wrong
onsdag den 12 maj 2010

Messaging gives you a
chance to do better
• No more showing the users a WSOD
• Messages are replayable
• Async communication opens up a crucial
windows of time for corrections
onsdag den 12 maj 2010

Event oriented communication
onsdag den 12 maj 2010

Publish and subscribe
• Everyone get’s a copy
• Removes behavioral
coupling
onsdag den 12 maj 2010

Billing
BillingService
OrderAcceptedEvent
Shipping
SalesService
ShippingService
Sales
Business events
onsdag den 12 maj 2010

Finally a chance to discuss non functional
requirements that business people understand
onsdag den 12 maj 2010

The mechanics of pub/sub
onsdag den 12 maj 2010

The mechanics of pub/sub
onsdag den 12 maj 2010

Becoming a subscriber
bus.Subcribe<IOrderAcceptedEvent>();
onsdag den 12 maj 2010

Publishing
bus.Publish<IOrderAcceptedEvent>(x=>
{
ProductId = 123,
Quantity = 10
....
});
onsdag den 12 maj 2010

It’s hard to get it right
the first time around
onsdag den 12 maj 2010

Versioning events using interfaces
public interface IOrderAcceptedEvent2 :
IOrderAcceptedEvent
{
string SomeNewProperty{ get;set; }
}
onsdag den 12 maj 2010

Long running
transactions
onsdag den 12 maj 2010

Use sagas to model long
running transactions
public
class
MySaga
:
Saga<MySagaData>,
IAmStartedByMessages<Message1>,
IHandleMessages<Message2>
{
public
void
Handle(Message1
message)
{
//
code
to
handle
Message1
}
public
void
Handle(Message2
message)
{
//
code
to
handle
Message2
}
}
onsdag den 12 maj 2010

Storing state
public
class
MySagaData
:
IContainSagaData
{
//
the
following
properties
are
mandatory
public
virtual
Guid
Id
{
get;
set;
}
public
virtual
string
Originator
{
get;
set;
}
public
virtual
string
OriginalMessageId
{
get;
set;
}
}
onsdag den 12 maj 2010

Timeouts
public
void
Handle(Message1
message)
{
this.Data.SomeID
=
message.SomeID;
RequestTimeout(TimeSpan.FromHours(1),
"some
state");
}
public
override
void
Timeout(object
state)
{
//
some
business
action
like:
if
(!Data.Message2Arrived)
ReplyToOriginator(new
TiredOfWaitingForMessage2());
}
onsdag den 12 maj 2010

Configuration
Developers:
use code
Administrators:
use config files
onsdag den 12 maj 2010

Hosting options
• Custom hosting
• Website
• Smartclient
• Commandline
• Generic host
onsdag den 12 maj 2010

Using the Generic Host
public class EndpointConfig:
IConfigureThisEndpoint,
AsA_Publisher
{
}
onsdag den 12 maj 2010

Using profiles to adapt to different
environments
onsdag den 12 maj 2010

NServiceBus role in
CQRS Style applications
onsdag den 12 maj 2010

NServiceBus is
opinionated
onsdag den 12 maj 2010

Why all these opinions?
onsdag den 12 maj 2010

Don’t use messaging
for queries
• Queries need to return relatively fast
• No benefit from the robustness that NSB
gives
• Use NSB to cache data close and use native
apis to get at that data
onsdag den 12 maj 2010

The end
• www.nservicebus.com
• www.udidahan.com/blog
• andreasohlund.blogspot.com
onsdag den 12 maj 2010