Event Driven Architecture

When we have to use an Event Driven Architecture?Initially, Current Practices and Future

What we will cover hereWhat is the Event Driven Apps?When is the Event Driven Architecture was

started?What is the Benefit?When we have to use?What is the Implementation in the real

world?What is the trend?

What is the Event Driven Apps?What is an Event?What is in an Event?What is the Reaction when an Event fires?

Ask Wiki!An event is a notable thing that happens

inside or outside your businessThe term event is often used interchangeably

to refer to both the specification (definition) of the event, and each individual occurrence (instance) of the event

Each event occurrence has an event header and event body as the delivered information

How’s an Event being consumed?It should be Published!And then Fired! And someone must Listen!And he /she will give some Reaction!Or, just ignore it!...

Simply, EDA will be as

Event Listener

Event Action

The Problem on Event TriggerTriggered by Predictable Events

Triggered by Un Predictable EventsRequired Active Listeners

The Problem on the ActionSynchronous Action

Asynchronous Action

When is the Event Driven Architecture was started?Four years from now, "mere mortals" will

begin to adopt an event-driven architecture (EDA) for the sort of complex event processing that has been attempted only by software gurus building operating systems or systems management tools, and sophisticated developers at financial institutions. (Roy Schulte, an analyst at Stamford, Conn.-based Gartner - 2003)

What is the Benefit?ScalableReaction basedStagedStaged + Reaction =

When we have to use?Best used for Asynchronous Flows of Work

and InformationWhen you need a Fast Responsive in front,

but Asynchronous process in the backgroundFire and Forget handling

Samples:The Web Server

What else? (Quiz)

ReplicationSchedulerReportingSynchronizationMessenger

Use these following key words:

Then add with word “Engine“

What is the Implementation in the real world?SOA based implementationMessaging based solutionAutomation solutionWorkflow solution

Sample of Messaging Solution

Sample of Workflow

Sample of Complex Workflow

Existing SampleNatPOS WindMills using SEDA

Implementation

What is the trend?Workflow enabled applicationFrom Enterprise Level to Single Instance

Application

To Single Instance: WWFSequential WorkflowState Machine WorkflowRule Driven Activities

Rules-driven Activities

Step2

Step1Rule1

Rule2

DataRules + data statedrive processing order

•Data-driven•Simple Conditions, complex Policies •Constrained Activity Group

State Machine Workflow

State2

State1Event

Event

External events drive processingorder

•Reactive, event-driven•Skip/re-work, exception handling•Graph metaphor

Sequential WorkflowStep1

Step2

Sequentialstructure prescribesprocessing order

•Prescriptive, formal•Automation scenarios•Flowchart metaphor

References:4 Years prediction on SOA implementation - Gartner

Event Driven Architecture – InfoQ articleMicrosoft .NET Framework 3.0, 3.5, WWF

NatPOS workflow engine - WindMills