In this presentation, I will explain event driven architecture, describe the different types of events, demonstrate how events can be related and orchestrated, and provide a basic understanding of how this method can drive the architecture of enterprise systems. In addition to understanding the concepts of event driven architecture, we will explore a working sample built using an open-source .NET messaging framework called MassTransit.

1. Event Driven Architecture
Chris Patterson
Senior Architect, RelayHealth
chris@phatboyg.com

2. Agenda
Enterprise Application Integration (EA-eye)
Events
Event Driven Architecture (ED-eh)
.NET sample using MassTransit

3. About Me
Enterprise Software Architect
Over 20 years of software development experience
Over 11 years at a Fortune 15 company
Proven track record with distributed, real-time systems

4. Enterprise Application Integration

5. Enterprise Application Integration
The process of linking applications within a single
organization together in order to simplify and automate
business processes
While avoiding sweeping changes to existing applications

6. File Transfer
Applications export and import files
Use various formats, requiring translation
Often loaded manually, infrequently
Affectionately known as ETL or SSIS

7. Shared Database
The mastermind of the axis of evil
Data is tightly coupled to multiple applications
Incremental, partial upgrade of application impossible
Primary reason for “forklift upgrades”

8. Web Services
Requires service to be available at invocation
Results in multiple call stacks, consuming resources
Yet another Remote Procedure Call (RPC, COM, CORBA)

9. Messaging

10. Messaging

11. Messaging
Defined data format
Asynchronous operation
Minimized coupling
Fault tolerance
Data Freshness

12. Defined Data Format
Mutual contract between producer and consumer
Internal formats remain private
Integration code remains at the edge of the application,
preventing internal changes from impacting the interface

13. Asynchronous Operation
Processes run in their own execution context
Originating process continues
Services need not be available at all times

14. Minimized Coupling
Additive model reduces change to existing systems
Reduces dependencies, increasing service reuse
Enables isolated testing of services

15. Fault Tolerance
Durable messaging improves recoverability
Compensating actions to handle partial failure

16. Data Freshness
Favors small data transfers of related data
compared to big files containing unrelated content
Minimizes data exchange latency

17. Events

18. Events
Represent a change in state
Self-contained
Uniquely Identifiable
Time relevant, not time sensitive
Sourced using messaging

19. Unique Identification
Enables idempotent handling of events
Improve traceability of related processing
Allows correlation with related events

20. Self Contained
A pure and complete representation of a specific event
No references to other data sources
No need to time sync to an additional source
Reduces dependencies, loosens coupling

21. Observable
Published events can be observed by multiple subscribers
Event stream processing

22. Event Types

23. Execution Events
Define the process flow
Order Coffee
Customer placed an order for coffee
Present Coffee
Coffee handed to customer

24. Lifecycle Events
Bookends around the process
Preparing Coffee
Barista began preparing a coffee
Coffee Prepared
Barista finished preparing a coffee

25. Management Events
Time period elapsed, Range or limit exceeded
Order Guarantee Exceeded
Your order within five minutes, or it’s free
Caffeine Junkie Alert
Orders of ten or more coffees require approval by FDA

26. Business Events
Found by observing the natural order of the business
Coffee Order Fulfilled
A coffee was ordered, prepared, and delivered
Material Shipment Arrived
Beans, milk, and cups delivered by brown

27. Event Driven Architecture

28. Event Driven Architecture
A method of building enterprise systems in which events flow
between decoupled components and services
A maintainable, sustainable, and extensible model for
building complex, distributed applications
Well suited for asynchronous, unpredictable environments

29. How is it different from SOA?

30. How is it different from SOA?
Event Driven Architecture
complements
Service Oriented Architecture

31. Service Oriented Architecture
Applications are composed at design-time
Linear flow between services
Predictable behavior
Request/Response is common, overused

32. Event Driven Architecture
Applications are composed at run-time
Asynchronous components
Reactive behavior
Natural fit for distributed systems

33. Autonomous Components
Triggered in response to an event
Independent - no coupling to event producer
Self-governing - makes decisions on how to react
Self-controlling - responsible for execution context
Self-contained - not part of an application

34. Event Producers
Publish messages representing an event
Often oblivious to the consequences of the generated event

35. Event Consumers
Subscribe to events by topic/type/selector
Handle events asynchronously
No performance penalty for additional consumers

37. MassTransit Key Points
Lightweight Service Bus Implementation
Loose coupling via publish/subscribe
Active Service Pattern
Supports MSMQ, ActiveMQ, TIBCO EMS
Open Source, Apache 2.0 License

38. “Event Driven
Architecture is...
programming without a call stack.”
-Gregor Hohpe, Google

39. Testing
Individual components testable in isolation
Fully unit-testable using mocks and stubs
Test-first development helps improve data contract

40. Debugging
Logging
Visualization Tools

41. Logging
Thorough logging with correlation information
Adjustable output configurable at runtime

42. Visualization Tools
Present code-based logic in a visual form
Aid in identifying composition problems
Should be viewable on operational systems

43. For More Information

44. Reading Material

45. Reading Material

46. Reading Material

47. Reading Material

48. Reading Material

49. Reading Material

50. Reading Material
Enterprise Integration Patterns (Hohpe, Woolf)
Patterns of Enterprise Application Architecture (Fowler)
SOA Patterns (Arnon Rotem-Gal-Oz, Eric Bruno, Udi Dahan)

51. Web Sites
MassTransit - http://masstransit.googlecode.com/
Topshelf - http://topshelf.googlecode.com/
Magnum - http://magnum.googlecode.com/

52. Contact Me
Chris@PhatBoyG.com
http://blog.PhatBoyG.com
http://twitter.com/PhatBoyG
http://PhatBoyG.LosTechies.com