Enterprise Integration Patterns

CS3300Fall 2015

Problem

● Modern systems in large enterprises are distributed across many platforms and comprised of many systems.

● How do we get them to operate together?

Categories● Information Portal : You have to access more

than one system to answer a particular status. The portal allows access to a single interface, that hides all the other systems.

● Data Replication : Sometimes the same data is stored across multiple systems (sales, accounting, billing). If the data changes, it needs to change everywhere.

● Shared Business Function : Same functionality is needed by multiple systems.

Categories● Service Oriented Architecture: Universal

services available to consumers● Distributed Business Processes: A single

transaction may span several systems.● Business to Business Integration: Providing

access outside the company (ie. Shipping company allowing customers to interact with their system for obtaining delivery dates)

Goal● Loose Coupling – reduce the amount of

assumptions one system has to make about another.

Simple Patterns (for communication)

● File Transfer : Have applications produce and consume files to read and write information

● Shared Database: Have applications store data in a common database

● Remote Method Invocation: Use an rpc mechanism (RMI, CORBA, COM, SOAP)

● Messaging : Asynchronous communication with custom formats

Messaging Components● Channels : virtual pipe connecting the sender and

receiver● Messages : atomic packet of data transmitted on

a channel● Pipes and Filters : chaining processing of

messages using channels● Routing : controlling the flow of messages that

have to go through many channels● Transformations : Converting information

between systems● Endpoints : a bridge between the message

system and the application

A Practical Implementation JMS

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JNDI - Java Naming and Directory Interface

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• Mapping human-readable names to machine names• Like DNS for web sites• Binding links names to objects (a filename to the physical file)• Context is a set of bindings. ( a file directory for example)• Name Service manages these contexts.

Different Architectures

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JMS Programming Model

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CQRS-ES● Command Query and Response Segregation● Event Sourcing

Traditional System Design

CQRS

Row 1 Row 2 Row 3 Row 40

2.5

5

7.5

10

12.5

Column 1 Column 2

Column 3

Why CQRS?● May perform 1000s of reads for each write,

thus each part can be optimized separately for transaction throughput. Each part can be scaled independently

● Commands are complex, Reads are simple. Each part can be optimized and maintained separately

● Can use two versions of the database, fully normalized for writes, consolidated for reads

● However it is not an architectural style, but a lower level concept

Concepts● Bounded Context : An autonomous business

component with clear boundaries – a self-contained business model

● Orders and Registrations● Conference Management● Payments● Submissions and Schedule Management

● Context Map : Showing the relationships between the bounded contexts

More Concepts● Command – request for the system to perform

and action MakeSeatReservation● Commands are transported on a command bus to

command handlers● Commands originate in either the UI or the Process

Manager

● Event – Something that has happened in the system, often in response to a command OrderConfirmed

● Multiple subscribers may handle an event

More components● ProcessManager – controls domain model

● Subscribes to events and creates commands● No business logic, just logic to figure out what

command to send

Event Sourcing● Events:

● Happened in the past● Are immutable● May cancel or negate a previous event● Are one way messages● Usually have parameters for additional information● Should describe a business intent

Event Sourcing● ES then is a way of persisting your

application's state by storing the history that determines the current state of the application.

Traditional ORM

Event Sourcing

Data Transfer Objects● These solutions frequently use DTO.● An object is created, forwarded to the UI. The

UI makes changes and the object is returned to the model for processing

● In CQRS, a DTO is sent to the UI, but the UI issues a command