OUR WAY TO MICROSERVICES

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DDD – CQRS - ES

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I’M ANDI PANGERAN

@andi_pangerancybercoding.wordpress.com

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Not that way…

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What we need right now is..

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Refactoring our logic

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AGENDA DOMAIN DRIVEN DESIGN

COMMAND QUERY RESPONSIBILITY SEGREGATION

EVENT SOURCING

AMQP MESSAGING

PROFT OF CONCEPT, SPRING BOOT + AXON FRAMEWORK

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DOMAIN DRIVEN DESIGN

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Introduction

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DOMAIN DRIVEN DESIGN

• .. For most software projects, the primary focus should be on the domain and domain logic.

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DOMAIN DRIVEN DESIGN

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DOMAIN DRIVEN DESIGNDESIGN

STRATEGIC DESIGN

TACTICAL DESIGN

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DOMAIN DRIVEN DESIGNDESIGN

STRATEGIC DESIGN

Bounded Context

Ubiquitouse Language

Context Map

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DOMAIN DRIVEN DESIGNBounded Context

General Ledger

Account Payable

Account Recieveable

AssetsManagement

InventoryBudgetControl

Accounting Application

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DOMAIN DRIVEN DESIGNUbiquitous Language

DOMAIN EXPERT

Developer

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DOMAIN DRIVEN DESIGNContext Map

Context mapping is a design process where the contact points and translations between bounded contexts are explicitly mapped out. Focus on mapping the existing landscape, and deal with the actual transformations later.

?Relation

General Ledger

Account Payable

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DOMAIN DRIVEN DESIGNShared Kernel

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DOMAIN DRIVEN DESIGNRelation Pattern

Open House Services

Customer – Supplier

Anti Corruption Layer

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DOMAIN DRIVEN DESIGNStrategic Design

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DOMAIN DRIVEN DESIGNDESIGN

Entity

Value Object

Aggregates

Domain Events

Layered Architecture

TACTICAL DESIGN

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Entity & Value Object

Entity…

An object fundamentally defined not by its attributes, but by a thread of continuity and identity.

Value Object…

An immutable object that describes some characteristic or attribute but carries no concept of identity.

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Aggregate

…

Cluster of associated objects that are treated as a unit for the purpose of data changes.

…

Aggregate enforce concictency

Order Line Items

Customer

Shipping Address

Aggregate Root

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Domain Events

…

Something meaningful that happened in the Domain…

Communicating state changes of Aggregates…

Immutable Value Objects

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Layered Architecture

Domain

Application

Infrastructure

Web

Por

ts

HTTP

Re

ques

t

Rest

Cont

rolle

rW

ebso

cket

Cont

rolle

rCo

mm

and

Hand

ler

Entity

Value Object

Repository

JPA

REPO

SITO

RY

SQL

DATA

BASE

Pers

iste

nce

Port

s

RABBITMQ

Messaging Ports

(AMQP)

EVENT (PUB – SUB)

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DOMAIN DRIVEN DESIGNTactical Design

Refactoring ?

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CQRS

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Introduction

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CQRS

Pioneered by Greg Young & Udi Dahan

In this context, » Commands = Writes» Queries = Reads

Command/Query Responsibility Segregation (CQRS) is the idea that you can use a different model to update information than the model you use to read information.

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CQRS

But why?

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Why Is CQRS needed ?

Read vs Write Capacity…

Scale read operations differently from write operationsSplit the concerns…

Simplicity in domain model by separating read and writes.

Decreased COMPLEXITY…

Write need validation and consequential logic.

Read have many representation model, and storage mechanism (polyglot storage)

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How Does CQRS work ?

Persistent View Model schema matches UI view model

Scale out as many copies as needed

Command captures the intent of the user

Commandbus deliver command to command

handler

A queue can be utilized to optimize write performance

After database is updated, publish result

to view model via eventbus

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How Does CQRS work ? Command

Commands encapsulate the user’s intent but do not contain business logic, only enough data for the command.

Command message handled by command handler.

Just once command handler / command message.

Command handler can reject a command, validation / bussines rules violation

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How Does CQRS work ? Event

Events describe changes in the system state.

An Event Bus can be utilized to dispatch events to subscribers.

Events primary purpose update the read model

Events can also provider integration with external systems

CQRS can also be used in conjunction with Event Sourcing.

Event Sourcing

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Introduction

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Traditional systems store current state

INSERT INTO charging_stationsVALUES (“CP001”, “Acme Corp.”, “Widget B”);

INSERT INTO charging_stationsVALUES (“CP003”, “ABC Widgets”, “Model-1”);

UPDATE charging_stationsSET model = “Widget A”WHERE identity = “CP001”;

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Traditional systems store current state

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Traditional systems store current state

keeping only the current state…

lot of valuable historic data is lost, e.g. the information about the time a state change happened, who invoked the change, and so on. This historic data may remind you of something called an audit log.

conceptual model…

there is no single model that could be used universally for every possible case that the system needs to address. Moreover, the structure of the application data tends to change overtime..

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Store the sequence of events that led up to the current state.

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populate the application state via projection

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Snapshoting

SNAPSHOT

CQRS

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Back to

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How Does CQRS work ? Persistent View Model

Read model can be denormalized RDBMS, document store, etc.

Optimize read model with different data storage technologies for different kinds of data (polyglot)

Eventually Concistence

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How do we apply the Concepts ?

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CORE

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CORE

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CORE

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CTM CORE

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CORE

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CTM CORE

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CORE

Advanced Message Queuing Protocol (AMQP)

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Introduction

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AMQP IN A NUTSHELL

A producer is a user application that sends messages

A exchange is message router that routes message to queue. There is Direct, Fanout, Topic Exchange

A queue is a buffer that stores messages

A consumer is a user

application that receives

messages.

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Fanout Exchange

A fanout exchange routes messages to all of the queues that are bound to it and the routing key is ignored. If N queues are bound to a fanout exchange, when a new message is published to that exchange a copy of the message is delivered to all N queues. Fanout exchanges are ideal for the broadcast routing of messages.

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Direct Exchange

A direct exchange delivers messages to queues based on the message routing key

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Topic Exchange

Topic exchanges route messages to one or many queues based on matching between a message routing key and the pattern that was used to bind a queue to an exchange.

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Sample Spring AMQP Configuration

Axon Framework

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Introduction

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Why Axon Framework

Compatibility with CQRS and ES …

Axon Framework is a Java Framework for scalable and high performance applications and being focused on making life easier for developers that want to create applications based on the CQRS principles and concepts, i.e. commands, events, aggregates, entities, sagas, etc. On top of that, it also supports event sourcing.

Integrability…

It supports the Spring Framework's configuration and dependency injection. It also uses Java annotations for building the domain model and event listeners without being tied to the Axon's specific logic.

Active development and support…

the latest version at the time of writing this was 2.4.4. It is actively developed, a new major version 3 is a work in progress. It has nice and detailed documentation and a sample project to showcase the code. The authors also provide commercial services such as support contracts, training, and consultancy.

Popularity…

The code repository on GitHub has more than 300 stars and 100 forks. The user community is active on the mailing lists and on the issue tracker.

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Axon FrameworkCommandBus

SimpleCommandBus…

It does straightforward processing of commands in the thread that dispatches them. After a command is processed, the modified aggregate(s) are saved and generated events are published in that same thread.

AsynchronousCommandBus …

It does processing of commands in new thread. After a command is processed, the modified aggregate(s) are saved and generated events are published in that same thread.

DisruptorCommandBus …

The DisruptorCommandBus takes a different approach to multithreaded processing. Instead of doing the processing in the calling thread, the tasks are handed off to two groups of threads, that each take care of a part of the processing. The first group of threads will execute the command handler, changing an aggregate's state. The second group will store and publish the events to the Event Store and Event Bus.

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Axon FrameworkSimpleCommandbus Configuration

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Axon FrameworkAsynchronousCommandBus Configuration

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Axon FrameworkDisruptorCommandBus Configuration

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Axon FrameworkEventBus

SimpleEventBus …

The SimpleEventBus just dispatches each incoming Event to each of the subscribed EventListeners sequentially. If an EventListener throws an Exception, dispatching stops and the exception is propagated to the component publishing the Event..

ClusteringEventsBus …

The ClusteringEventsBus allows application developers to bundle EventListeners into Clusters based on their properties and non-functional requirements. The ClusteringEventBus is also more capable to deal with Events being dispatched among different machines. Contains two mechanisms: the ClusterSelector, which selects a Cluster instance for each of the registered EventListeners, and the EventBusTerminal, which is responsible for dispatching Events to each of the relevant clusters..

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Axon FrameworkSimpleEventBus Configuration

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Axon FrameworkClusteringEventBus Configuration

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Axon FrameworkEvent Store

FileSystemEventStore…

The FileSystemEventStore stores the events in a file on the file system. It provides good performance and easy configuration. Not a suitable implementation for production environments

JpaEventStore …

The JpaEventStore stores events in a JPA-compatible data source. Unlike the file system version, the JPAEventStore supports transactions. The JPA Event Store stores events in so called entries. To use the JpaEventStore, you must have the JPA (javax.persistence) annotations on your classpath..

JDBC Event Store …

The JDBC event store uses a JDBC Connection to store Events in a JDBC compatible data storage. Typically, these are relational databases. Theoretically, anything that has a JDBC driver could be used to back the JDBC Event Store.

MongoDB Event Store …

Use mongodb to store Events.

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Axon FrameworkJdbcEventStore Configuration

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Axon FrameworkMongoDb EventStore Configuration

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Axon FrameworkAggregate Repositories

GenericJpaRepository…

This is a repository implementation that can store JPA compatible Aggregates. It is configured with an EntityManager to manage the actual persistence, and a class specifying the actual type of Aggregate stored in the Repository.

EventSourcingRepository …

The EventSourcingRepository implementation provides the basic functionality needed by any event sourcing repository in the AxonFramework.

HybridJpaRepository…

The HybridJpaRepository is a combination of the GenericJpaRepository and an Event Sourcing repository. It can only deal with event sourced aggregates, and stores them in a relational model as well as in an event store. When the repository reads an aggregate back in, it uses the relational model exclusively..

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Axon FrameworkSample Repository Configuration

Spring Boot + Axon Framework

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Proft Of Concept

QUESTIONS ?

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Recommended Reading

Thanks

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