LagomReactive microservices framework

#NightClazz @Lagom12/05/16

Fabrice Sznajderman@fsznajderman

Agenda

● Core concepts

● Lagom framework

● Hands on Lagom

Who I am?

Fabrice Sznajderman ○ Java/Scala/Web developer

■ Java/Scala trainer■ Co-organizer of Scala IO 2016■ Contributor on Lagom

● BrownBagLunch.fr

Chapter 1

CoreConcepts

Agenda

● Microservices architecture

● CQRS

● Event Sourcing

Core concepts

Core concepts

MicroservicesArchitecture

Monolithic vs Microservices

Monolithic issues

● All features are concentrated in one app

● One technology used (silver bullet?)

● Complexity rising over time● new comers have difficulties to

dive into code base

Microservices-based Architecture

Reactive Microservices Architecture: Design Principles for Distributed Systems - James Boner http://www.oreilly.com/programming/free/reactive-microservices-architecture.html

Microservices-Based Architecture is a simple concept: it advocates creating a system from a collection of small, isolated services, each of which owns their data, and is independently isolated, scalable and resilient to failure. Services integrate with other services in order to form a cohesive system that’s far more flexible than the typical enterprise systems we build today.

What is a microservice?Standalone component

What is a microservice?Isolated

What is a microservice?Own its data

What is a microservice?Located microservice

What is a microservice?Communication by asynchronous message

What is a good microservice ?

Answer with 3 questions ...

Question 1Does my service do only one thing?

If you can state a microservice’s full purpose with a short sentence, your service is OK!

“This service manages users’ accounts”

Question 2Is my service autonomous?

A service should be responsible for its own behavior. It shouldn’t rely on other services to do its job.

“An autonomous service would accept the any request regardless of the status of others services.”

Question 3Does this service own its own data?

A service “owns” data if it is the sole writer and the sole reader of the database where the data lives

“Data can be accessed only throught the service interface, no directly”

Anti-pattern

● Adapted use-case?● Transactionnal● Distributed monolithic layers● “Don’t Repeat Yourself”● Shared data repository

That implies challenges

● Organisational impacts● Monitoring of services● Locating service● Test strategy● Distributed development

environment

Reading

Reactive Microservices Architecture by Jonas Boner

CQRS Core concepts

CQRS stands for

● Command● Query● Responsability● Segregation

Traditional approach

Traditional approach

● Using the same model for read and write

● Read & write have different needs○ Representation of data can

take several forms○ Update side contains

validation rules● All together rises complexity● Performance issues

Write : Normalization, consistency, transactional...

Read : Denormalization, scalability, performance...

Needs between read and write are not the same.

http://martinfowler.com/bliki/CommandQuerySeparation.html

Facts

Command : Change the state of a system but do not return a value

Queries : Return a result and do not change the observable state of the system (are free of side effects)

Principle is that we divide our model into two sharply separated categories:

http://martinfowler.com/bliki/CommandQuerySeparation.html

CQRS approach

CQRS approach

CQRS approah

● Each model are on ○ separate logicals processes○ separate hardware

● Database :○ shared ○ unique per model

● Unique model with differente interfaces

Several manners to implement

Other architecture

CQRS approah

● Not a silver bullet, every case doesn’t fit with this CQRS approach.

● Doesn’t apply CQRS on whole system, only be used on specific portions of system (bounded context - DDD)

Cautions

Next

CQRS design fits well with Event Sourcing pattern...

EventSourcing

Core concepts

Traditional approah Active record

Traditional approah Active record

Traditional approah

● Only final state is captured● Debugability & tracability not

really easy● Complexity with mapping O & R● Performance issue (update)

How we have reached this state?

Active record

Event Sourcing approach

● Don't update the current state of objects

● Save the events that lead to the current state

Different approach

Event Sourcing approach

● Complete log of every state change

● Debugability & tracability come easy

● Good performance (commit log)

and more …

Benefits

● Complete rebuild● Temporal query● Event replay

Event Sourcing approach More benefits

● Commands are going to change the state (or not)

● Each state change creates an event● Order of events must be preserved

Event Sourcing approachHow does it works?

● Command’s name describe an action to do (imperative)

● Event’s name describe an action in the past

Event Sourcing approachRemarks

Event Sourcing approachRestore state into model

Event Sourcing approachDeleting an object

Update the query side with deletion of bank account.

Event Sourcing approachSnapshot

● Several events will be created● Restore all events to reach one state

might be expensive● To avoid this, we use a snapshot

LagomFramework

Chapter 2

Agenda

● Big picture of Lagom

● Project structure

● My first microservice

Lagom framework

Big pictureof Lagom

Big picture of Lagom

First of all, … Lagom pronounce :

What is Lagom?

● Microservices framework for a

system of microservices

● Based on the Reactive principles

● A fully integrated development

environment

Which language?

● Core of framework written in

Scala

● Developments are in Java

● Scala version migth be available

soon

Main features

● Service API

● Persistence API

● Development Environment

● Production Environment

Service API

● Interface as descriptor

● Defined API of exposed services

● Synchronous request/response

● Asynchronous streaming

message

Persistence API

● Provides event-sourced

persisted entities

● CQRS Read side

● Entry point for events handlers

Development Environment

● One command to start all

services

● Hot reload of your code

● Several services provided out of

the box

● IDE Integration

Production Environment

● ConductR for production

environment

● Scaling

● Deployment

● Monitoring

Communication protocols

● Polyglot systems

● HTTP, WebSocket, JSON are

standards

● can consumed

● can be consumed

Component technologies

● Collection of technologies

● Some come from Lightbend

● Others are third-party and

open-source

Component technologies

● Java 8 (& Scala)● Immutables● SBT● Jackson● Cassandra● Play framework● Guice● Akka : Persistence, Pub/Sub,

cluster● Akka Stream : Streaming part● SLF4J & Logback

● Asynchronous & non blocking as

default

● Distributed persistence : ES /

CQRS as default

● Circuit breaker (as default)

● Productivity for developers :

Expressive service interface

Design philosophy

Project Structure

with Lagom

Activator

activator sampleProject lagom-java

● Engine provided by Lightbend

● Create project from template

● Template name for Lagom: lagom-java

● Activator must be installed apart

● Generated a new project :

Project tree

SBT build file

● Project configuration

● Describe all modules

● Describe all dependencies per module

● Host all parameters for project

○ cassandra

○ service locator

○ etc

Service declaration

● One service is composed of 2 sub-

projects

○ API

○ Implementation

● Implementation depends on API

SBT build fileorganization in ThisBuild := "sample.helloworld"

// the Scala version that will be used for cross-compiled librariesscalaVersion in ThisBuild := "2.11.7"

lazy val helloworldApi = project("helloworld-api") .settings( version := "1.0-SNAPSHOT", libraryDependencies += lagomJavadslApi )

lazy val helloworldImpl = project("helloworld-impl") .enablePlugins(LagomJava) .settings( version := "1.0-SNAPSHOT", libraryDependencies ++= Seq( lagomJavadslPersistence, lagomJavadslTestKit ) ) .settings(lagomForkedTestSettings: _*) .dependsOn(helloworldApi)

Service imported

● One service could be imported as

dependency

● Just declare it and it will start as others

Launch services

● One command to launch all Lagom’s

service : sbt runAll

● Several services are launched

○ Cassandra

○ Service locator

○ service gateway

○ All services that you declared

Launch one service

● One command to launch one Lagom’s

service : sbt project_name/run

● no more services are launched

● One service Locator must be available

apart.

Locator service

● All services register on this locator

● By default, one service locator is started

● It can be started apart

Cassandra embedded

● One instance of Cassandra is started by

default

● It can be unactivate if no persistence is

required

● It can be started apart

● Cassandra’s client can be used to

explore tables

Mapping of one Service

Write a servicewith Lagom

Demo

Here, we will see :

○ Global configuration of project

○ Service Interface - Descriptor

○ Related implementation

○ All stuffs linked with persistence (CQRS-EventSourcing)

Just an information !

● 5 days ago, the API has change !!!

ServiceCall<Id,Request, Response>

interface ServiceCall<Request, Response> {

CompletionStage<Response> invoke(Request request);

//others methods

}

Ok, now we can dive into dark side...code! ;)

Thank you!Next …

Hands on!Chapter 3