Microservices in Java and Scala (sfscala)

@crichardson Microservices in Java and Scala Chris Richardson Founder of Eventuate.io Founder of the original CloudFoundry.com Author of POJOs in Action @crichardson chris@chrisrichardson.net http://microservices.io http://eventuate.io http://plainoldobjects.com Copyright © 2015. Chris Richardson Consulting, Inc. All rights reserved

@crichardson About Chris Consultant and trainer focusing on microservices (public class: April 28th, Oakland, CA) http://www.chrisrichardson.net/

@crichardson About Chris Founder of a startup that is creating a platform that makes it easy for application developers write microservices (http://eventuate.io)

@crichardson For more information http://bit.ly/eventsmarch17

Agenda Why a pattern language for microservices? Monolith architecture vs. microservices Developing microservices with event sourcing and CQRS Microservices in Java Microservices in Scala Example: real-time, collaborative Kanban board application

@crichardson In 1986… http://en.wikipedia.org/wiki/Fred_Brooks

@crichardson Yet 30 years later…. If you __________________ a puppy will die Therefore you must _______________

@crichardson Quiz - ﬁll in the blanks…. mutate state use monads use objects use functions block a thread use async. make a REST call send a messageuse Spring use ….

@crichardson How we make decisions Decide using emotions Rationalize with our intellect http://en.wikipedia.org/wiki/Mahout

@crichardson The structure of a pattern = Great framework for discussing and thinking about technology

@crichardson The structure of a pattern Resulting context aka the situation Name Context Problem Related patterns (conﬂicting) issues etc to address Forces Solution

In theory: We can build a modular monolith But in practice: We build a big ball of mud

Microservices are not a silver bullet but …

@crichardson The beneﬁts typically outweigh the drawbacks for large, complex applications

@crichardson Build and deliver better software faster

@crichardson Easily try other technologies ... and fail safely

Data management patterns Database per Service Event-driven architecture Shared database Event sourcing Transaction log tailing Database triggers Application events CQRS Database architecture

Database per Service Orders Service Customer Service Order Database Customer Database Sharded SQL NoSQL DB

@crichardson Customer management How to maintain invariants? Order management Order Service placeOrder() Customer Service updateCreditLimit() Customer creditLimit ... has ordersbelongs toOrder total Invariant: sum(open order.total) <= customer.creditLimit ?

@crichardson Event-driven architecture

@crichardson How atomically update database and publish an event Order Service Order Database Message Broker insert Order publish OrderCreatedEvent dual write problem ?

@crichardson Reliably generating events

@crichardson Use event-sourcing Event table Aggregate type Event id Aggregate id Event data Order 902101 …OrderApproved Order 903101 …OrderShipped Event type Order 901101 …OrderCreated

@crichardson Replay events to recreate state Order state OrderCreated(…) OrderAccepted(…) OrderShipped(…) Events Periodically snapshot to avoid loading all events

@crichardson Command Query Responsibility Segregation (CQRS) Command side Commands Aggregate Event Store Events Query side Queries (Materialized) View Events

@crichardson Query-side design Event Store Updater View Updater Service Events Reader HTTP GET Request View Query Service View Store e.g. MongoDB Neo4J CloudSearch update query

Multiple ﬂavors of client frameworks “Traditional Java” mutable object-oriented domain objects https://github.com/cer/event-sourcing-examples/tree/master/ java-spring Functional Scala with immutable domain objects https://github.com/cer/event-sourcing-using-scala-typeclasses Hybrid OO/Functional Scala with immutable domain objects https://github.com/cer/event-sourcing-examples/tree/master/ scala-spring

@crichardson The Customer aggregate creditLimit creditReservations : Map<OrderId, Money> Customer List<Event> process(CreateCustomerCommand cmd) { … } List<Event> process(ReserveCreditCommand cmd) { … } … void apply(CustomerCreatedEvent anEvent) { … } void apply(CreditServedEvent anEvent) { … } … State Behavior

@crichardson Familiar concepts restructured class Customer { public void reserveCredit( orderId : String, amount : Money) { // verify // update state this.xyz = … } public List<Event> process( ReserveCreditCommand cmd) { // verify … return … new CreditReservedEvent(); } public void apply( CreditReservedEvent event) { // update state this.xyz = event.xyz }

@crichardson Customer command processing

@crichardson Customer applying events

@crichardson Creating an order save() concisely speciﬁes: 1.Creates Order aggregate 2.Processes command 3.Applies events 4.Persists events

@crichardson Event handling in Customers 1. Load Customer aggregate 2. Processes command 3. Applies events 4. Persists events Triggers BeanPostProcessor Durable subscription name

@crichardson MongoDB view: customer and their order history { "_id" : "0000014f9a45004b 0a00270000000000", "_class" : "net.chrisrichardson…..views.orderhistory.CustomerView", "version" : NumberLong(5), "orders" : { "0000014f9a450063 0a00270000000000" : { "state" : "APPROVED", "orderId" : "0000014f9a450063 0a00270000000000", "orderTotal" : { "amount" : "1234" } }, "0000014f9a450063 0a00270000000001" : { "state" : "REJECTED", "orderId" : "0000014f9a450063 0a00270000000001", "orderTotal" : { "amount" : "3000" } } }, "name" : "Fred", "creditLimit" : { "amount" : "2000" } } Denormalized = efficient lookup

@crichardson Query-side event handler that updates customer view

@crichardson Updating and query view using Spring Data for MongoDB...

@crichardson Functional Customer aggregate Customer creditLimit creditReservations … CustomerAggregate processCommand(Account, Command) : Seq[Events] applyEvent(Account, Event) : Account Immutable state Behavior

@crichardson Aggregate type classes Used by Event Store to reconstitute aggregates Hardwired

@crichardson Customer Aggregate…. State Behavior

@crichardson …command processing…

@crichardson … applying events

@crichardson Kanban board example

@crichardson Architecture Create/update boards and tasks Change notiﬁcations Materialized views Event Store

Summary Microservices are not a silver bullet but they are the best choice for large/complex applications Use an event-driven microservices architecture Build services using event sourcing + CQRS Using a language/framework speciﬁc programming model

@crichardson @crichardson chris@chrisrichardson.net http://bit.ly/eventsmarch17 Questions?

Microservices in Java and Scala (sfscala)

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