Event-Driven Microservices Architecture: Reason, how and where to apply

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Event Driven Architecture Reason, how and where to apply Luram Archanjo

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Who am I? ● Software Engineer at Sensedia ○ Edenred ○ Cielo ● MBA in Java projects ● Java and Microservice enthusiastic

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Agenda ● Microservices ● REST ● Message Driven Architecture ● Event Driven Architecture ● Questions

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Moving to Microservices Feature A Feature B Feature C Monolith Microservice Microservice Microservices Microservice

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● Communication ● Security ● Network failures ● Observability ○ Metrics ○ Logs ○ Tracing Challenges with Microservices

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Communication Microservice Microservice Microservice Microservice Microservice Microservice Microservice Microservice

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Representational state transfer (REST)

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REST - Representational State Transfer GET GET POST PUT DELETE /movies /movies/{movieId} /movies /movies/{movieId} /movies/{movieId}

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● Web already built on top of HTTP ● Easy to understand ● Variety of http implementation in any languages ● Loose coupling between client and server Representational State Transfer

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Microservice Communication Microservice Microservice Microservice Microservice Microservice Microservice Microservice Microservice

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Cheers We have a system

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Unfortunately We will have problems

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Microservice Communication Microservice Microservice Microservice Microservice Microservice Some kind of problems • Crash of service • Slow response time • Change of interface

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How to handle it?

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There is something worse

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Microservice Communication Database per service Microservice Microservice Microservice Microservice Microservice

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Code is easy, state is hard

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Event-Driven Architecture

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First, we need to learn the difference between Synchronous vs Asynchronous

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Synchronous vs Asynchronous

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Reasons to Send a Message

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Reasons to Send a Message

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Message-Driven Architecture Producer Consumer Message Broker Producer Producer Consumer Consumer Advantages • Durable Message • Guaranteed delivery • Decoupling

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Message-Driven Architecture Producer Consumer Message Broker Producer & Consumer Pattern One message, one consumer! Consumer Consumer

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Message-Driven Architecture Publisher Subscriber Message Broker Publisher & Subscriber Pattern One message, many subscribers! Subscriber Subscriber

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Event-Driven Architecture

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Event-Driven Architecture Event-Driven Architecture Message-Driven Architecture Broker Producer Consumer

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Event-Driven Architecture Event Producer Event Consumer Event Broker Fire & Forget Pattern One event, many consumers! Event Consumer Event Consumer

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Events are facts that happened in the system

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Types of events Low level event “CRUD” Events ● OrderCreated ● OrderUpdated ● OrderDeleted Domain level event Business Events ● RequestedOrder ● ApprovedOrder ● RejectedOrder

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Saga Pattern

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Saga Pattern Orchestration Choreography Event Producer Event Mediator Event Consumer Event Consumer Event Event Broker Producer Consumer Event Consumer

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“We can query an application's state to ﬁnd out the current state of the world, and this answers many questions. However there are times when we don't just want to see where we are, we also want to know how we got there.” Martin Fowler, 2005

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Event Sourcing Persists the state of a entity as a sequence of state-changing events Whenever state of entity changes, a new event is appended to the list of Events Saving an event is a single operation (atomic) The application reconstructs an entity’s current state by replaying the events

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Event Sourcing

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CQRS Optimize different nonfunctional requirements for read and write Write Delay Eventual Consistency Database as event publisher (optional) Data Projection and Materialized View Command Service Microservice Event Store Query Service Microservice

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Eventual Consistency Command Service Microservice Event Store Query Service Microservice I want pizza Pizza = ? Pizza = Preparing

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Event Ording 0 100 80 Events Account: Created Deposit: R$ 100 Withdraw: R$ 20 Withdraw: R$ 20 Ordering Not Ordering 60 0 0 0 100

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Event Stream Event #1 Event #2 Event #3 Event #4 Event #5 Event #6 Event #7 Replay Timeline

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Why we are talking about Event Driven Architecture (EDA)

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“By 2020, event-sourced, real-time situational awareness will be a required characteristic for 80% of digital business solutions, and 80% of new business ecosystems will require support for event processing.” Top 10 Strategic Technology Trends for 2018

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Summary 2º Place 1º Place 3º Place It enables an application to maintain data consistency across multiple services without using distributed transactions It scales well to a very large number of users and allows new services to be added without breaking the streams of data that are currently deployed Analytics ● Audit ● Near real time ● Machine learn