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Messaging Patterns. An alternative approach to modeling with ESB’s. Jimmy P @ pjimmy [email protected] http:// www.blog.thejimmyp.com. Outline. Some Context Some Problems Intro to Messaging Systems Some Solutions And The Focus Some Patterns. Platform. Temporal. Spatial. Afferent. - PowerPoint PPT Presentation
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Messaging PatternsAn alternative approach to modeling with ESB’s
Jimmy P@[email protected]://www.blog.thejimmyp.com
OutlineSome Context
Some Problems Intro to Messaging SystemsSome Solutions
And The FocusSome Patterns
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
It’s mainly about coupling
Efferent
Afferent
Platform Temporal
Spatial
Efferent
Afferent
Platform Temporal
Spatial
• AKA interoperability
• Most RPC and other common messaging technologies are platform
• dependent in painful places
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• When A calls B synchronously B’s processing time affects A
A BA Calls B
B Returns
A Blocks WhileB Processes
B Processes
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• Where are the components physically?
• Is there multiple instances, and where are they?
• How do I decide which of multiple logically identical components I should send my message to?
• What happens if the only physical instance I know of is down?
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• Afferent - What do I take a dependency on?
• Efferent - What takes a dependency on me?
But it’s also a little about data loss
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
When Servers Crash
DBApp[HTTP] $$ Order
TxCall 1 of 3
Call 2 of 3
Critical Windows Patch
RollbackWhere’s the order!?
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
App[HTTP] $$ Order
Tx
When Databases Are Down
Exception
Write to log
DBCall 1 of 3
Down
Where’s the order!?
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
TxApp[HTTP] $$ Order
When Deadlocks Happen
DBCall 1 of 3
Deadlock
ExceptionWrite to log A B
Call 2 of 3
Where’s the order!?
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
Data Loss Using Web Services
A B C D
WSDB
[HTTP] Invoke
$$ Order
Deadlock
Rollback
Not Rolled back
So What is SOA and what are messaging systems?
Bus vs. Broker vs. RPC
Service C
Service B
Service A
Broker
.NETWCF
Service
JAVA WEB
Service
SAP
SVC A
BUS
SVC B
BUS
SVC C
BUS
External JSON
ServiceSalesForc
e
Service F
Service C
Service D
Service E
What makes up a messaging system
Messages travel between queuesQueues are persistent stores located on the
machine the service is deployed toQueues can persist messages to non volatile
storage in case of faultsAdding and removing messages from queues
can be transactionalQueues provide us with our asynchronous
behavior
So How does messaging help with coupling?
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• XML for message format & XSD for message schema
• Communication protocol and addressing is a problem
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• Asynchronous messaging
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• Create logically autonomous services
• Address services logically not physically
Some diagrams adapted from material by Udi Dahan – The Software Simplisthttp://www.udidahan.com
Efferent
Afferent
Platform Temporal
Spatial
• Use the message schema to create a level of indirection between services so there is no direct dependency
Service A
Communications Infrastructure
Schema A
Service B
Schema B
And with data loss?
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
Tx
Messages are transactions
Q$$ Order
App
Receive
DBCall 1 of 3
Rollback
Call 2 of 3
Rollback
The order is back in the queue
Slide courtesy of Udi Dahan – The Software Simplist
http://www.udidahan.com
Web Services with Messaging
MessagingGateway
A B C D
WS
Msg
DB
$$ Order
[HTTP] Invoke
The message won’t be sent if there’s a failure
So messaging is the silver bullet ;)
Let’s look at some patterns
Return Address Pattern
Provides a place to specify a physical address per message, allowing of logical addressing per message type
Now EndpointA can do other work while waiting for it’s response
Load Balancing with Return Address
EndpointA can specify an endpoint under less load to process the response if it has that information
Correlated Request/Response
An extension of Return AddressAllows services to maintain state
Multiple Responses with Correlated
Request/Response
User may not know or care about ALL of the responses
Ultimate in SRP
Multiple Handlers with Correlated
Request/Response
Publish/Subscribe
Allows us to add Events to our modeling arsenal By subscribing to message types from a logical address we are
only coupled to schema This allows us to trivially increase parallelism as required
Simpler more Robust systems
Modeling Business with Messaging Systems
Resources and Thankshttp://www.nservicebus.com/[email protected]@[email protected] If you are really keen watch this space
http://www.udidahan.com/training/ a truly life changing course
And many thanks to Udi for letting me steal his pretty animated slides and a diagram here and there. Made me look better than I deserved and saved me heaps of work
