EVENT DRIVEN
ARCHITECTURE
Chris Patterson
Senior Architect, RelayHealth
chris@phatboyg.com

EVENT DRIVEN
ARCHITECTURE
Chris Patterson
Senior Architect, RelayHealth

Agenda
Review Enterprise Application Integration
Introduce Event Driven Architecture
Define Events
.NET sample using MassTransit

About Me
Enterprise Software Architect
20+ years in commercial software development
11+ years at a Fortune 15 company
Proven history with distributed, real-time systems
Microsoft Visual C# MVP

ENTERPRISE APPLICATION
INTEGRATION

ENTERPRISE APPLICATION
INTEGRATION
Linking applications in an organization together to
simplify and automate business processes

Shared Database
Multiple applications coupled to single schema
Unclear ownership of schema
Edges between applications blurred
Linked servers for SQL to SQL RPC
Changes often affect multiple applications

File Transfer
Extract - Transform - Load (ETL)
Asynchronous
Simple interoperability through common formats
Timeliness of data can lead to inconsistencies
Large data volume containing unrelated data
Ownership of files, cleanup, versioning

Web Services
Explicit Contract (WSDL, DataContract)
Synchronous Operation leads to sequencing
Services must be available at invocation
Nested call stacks fragile, consume resources
Remote Procedure Call (RPC, COM, CORBA)
The network is unreliable

MESSAGING

Message Exchange
Create Process
Send Receive

A-Synchronicity
Message producers are non-blocking
Fire and forget
Message consumers run in their own process
Introduces a more complex programming model

Minimized Coupling
Eliminates temporal coupling
Enables isolated testing of services
Reduces dependencies, increasing service reuse

Explicit Contract
Agreement between producer and consumer
Internal data structure remains private
Integration points remain at the application’s edge
Eliminates propagation of internal changes

Fault Tolerance
Messages improve recoverability
Durable message transports

Data Availability
Enables small, frequent transfers of related content
Distribute system load over a wider time window

EVENT DRIVEN
ARCHITECTURE

EVENT DRIVEN
ARCHITECTURE
A method of building enterprise systems in which events
flow between decoupled components and services

Another Architecture?
Service Oriented Event Driven
Architecture Architecture

Service Oriented Event Driven
Architecture Architecture
Complimentary

Service Oriented Event Driven
Architecture Architecture
Complimentary

SOA 1.0
Applications are composed using a designer
Synchronous programming model
Step-by-step (F10) flow through services
Majority of interactions are request/response

Event Driven Architecture
Components are assembled at run-time
Asynchronous programming model
Reactive behavior
Leverages one way, fire and forget, messaging

Autonomous Components
Defined by responsibility
Independent
Self-governing - makes decisions on how to react
Self-controlling - responsible for execution context
Self-contained - not part of an application

Event Producers
Publish events
Oblivious to consumer reactions
Unaffected by high number of consumers

Event Consumers
React to events
Subscribe by topic/type/selector
Asynchronous operation

Business Components
Logical grouping of autonomous components
Represent a complete business process

COMMANDS

Commands
Tell a component or service to do something
Initiated by an event, interaction, etc.
Use correlation for tracing, idempotence
Sent using messaging (not published)

Reset Password
User initiates a password reset
Password service sends reset email
User clicks link in email

Message Body
public class ResetPassword
{
public Guid RequestId { get; set; }
public string Username { get; set; }
}

Compared To...
public void ResetPassword(string username)
public class ResetPassword
{
public Guid RequestId { get; set; }
public string Username { get; set; }
}

EVENTS

EVENTS
Represent a change in state

Self Contained
A pure and complete representation of a specific event
Time relevant, not time sensitive
Avoid references to internal data
Reduces dependencies, loosens coupling

Identified
Each event should have its own unique identifier

Related
Related events should share a common identifier
Allows event tracing (the new F11)
Assists in combining events into processes

Observed
Events are published as messages
Multiple components can subscribe to the same event

EVENT TYPES

Business Events
Map to real world events that occur in business
Item Added to Cart
Invoice Received
Order Shipped
Payment Requested

Lifecycle Events
Notifications related to the life of a state or process
Preparing Shipment / Shipment Prepared
Authorizing Payment / Payment Authorization
Complete
Session Started / Session Completed

Management Events
Relate events to time, ranges, limits
Timely Service Guarantee Exceeded
Your order within five minutes, or it’s free
Popular Item Notification
Items with a 5x increase in sales in an hour

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

“EVENT DRIVEN
ARCHITECTURE IS...
programming without a call stack.”
-Gregor Hohpe, Google

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

Logging
Thorough logging with correlation information
Log level configurable at runtime

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

FOR MORE
INFORMATION

Reading Material

Reading Material

Reading Material

Reading Material

Reading Material

Reading Material

Reading Material

Web Sites
MassTransit.GoogleCode.com
Topshelf.GoogleCode.com
Magnum.GoogleCode.com

CONTACT ME
Chris@PhatBoyG.com
http://PhatBoyG.LosTechies.com
twitter: @PhatBoyG
voice: text “cmp” to 50500