A Journey from Hexagonal Architecture to Event SourcingCarlos Buenosvinos (@buenosvinos)

Polycon, October 6th, 2017 Barcelona

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Who am I? Carlos Buenosvinos

• Technical Director @ XING • Consultant • +10 years on Tech Leadership

(CTO, VP of Engineering, Director) • Teams up to 100 people • E-Commerce, E-Learning,

Payments, Classifieds, Recruiting • Atrápalo (500M EUR),

PCComponentes (300M EUR)

@buenosvinos3

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Domain-Driven Design in PHP Book Carlos Buenosvinos, Christian Soronellas and Keyvan Akbary

https://leanpub.com/ddd-in-php

I want to tell you a real story about…

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a Company evolving its architecture.

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Spaghetti Architecture

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• Multiple Application Entry Points - create_user.php, delete_user.php, …

• Infrastructure and Domain Together - PHP and SQL within HTML

• Lack of Testing • Difficult to Maintain

Framework Fanboy Architecture

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• Single Application Entry Point - app.php

• Some structure is present (MVC) • Still Mixing Infrastructure and Domain

- Long Controllers with SQL and Business Logic, Dummy Entities (getters and setters)

• No testing or using Web Framework • Difficult to upgrade Infrastructure

Components

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Application Service

Any Random Action in a Web

Controller

I receive an email

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Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

Benefits of Hexagonal Architecture

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• Separation of Concerns • Decoupled from the Framework • Delays Infrastructure Decisions

- Persistence Storage or Delivery Mechanism (Web, API, CLI, etc.)

• Easy to Test - Testing Application Services (or CH) - Testing Entities - Mocking between the boundaries

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Web Controller

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Application Service

Moving to Hexagonal Architecture

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• Pick an action in the Web Controller - Identify Infrastructure references

(ORM, HTTP Rest Calls, Caching, etc.) - Extract Variable and to the top

• Extract Business Logic into Application Services (Copy and Paste)

• Move Infrastructure references away - ORM flush() into Repositories

• Start Unit Testing from Application Services

New Tech Policies in the Team:

1. Everything New: Hexagonal Architecture

2. Touching an Old Feature: Boy Scout Rule ("Always leave

the campground cleaner than you found it.”)

3. 100% Coverage in the Application Services

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Coverage going up!

Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

At this point, you can be consultant too!

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“… and I want to notify the user by email, logging and sending a BI tracking” Company’s Product Owner

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Team starts to face new issues

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• # of Dependencies Grows • Application Service complexity Grows • More Chances to Introduce Bugs

- More developers touching the same file (Main Task and Subtasks mixed)

• More Subtasks in the same feature, Worse Performance!!

Domain Events to the rescue!

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Domain Event Example

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Firing a Domain Event

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Domain Event Publisher Example

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Domain Event Listener

(Elastic Example)

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Domain Event Listener

(MySQL Example)

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Domain Event Listener

(Rabbit Example)

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Registering Domain Event

Listeners

Sync all the things!

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TechPoliciesAdded (ok, it’s a bad joke!)

1. Subtasks of a Feature are developed in a different

Application Service and attached via Listener

2. Fire any new Event that Business may be interested

3. Let’s have a TV screen to monitor realtime Business

metrics to be proactive.34

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Composition by Domain Events

Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

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“Hey team! Have you realised that the item page is getting quite slow?” Company’s Product Owner

Perfomance! Multiple Costly Requests (#, external, joins, etc.)

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Async all the things!

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Have you ever sent an email about something

that didn’t finally happen?

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Problem #1: 2 Infras / 1 Tx

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What strategies to deal with these inconsistencies can we follow?

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• Let inconsistencies happen - The Command Handler will manage

itself (firing ArticleWasAdded, sent to RabbitMQ, but failed Database Tx)

- Feasible for most operational tasks (sending email, non-critical tracking, etc.)

• New Article Added Action and its Event persisted in the same Tx. Then Worker to move Events to Rabbit.

• Global TX (Noooooooooo!)

Problem #2: Diff(ORM) !== Diff(Events)

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Max Performance!

Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

Buenosvinos Maturity Model

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Level 1: Spaghetti Level 2: Framework Fanboy Level 3: Hexagonal Architecture Level 4: Hex. + Domain Events Level 5: Stepping Stone (CQRS) Level 6: Event Sourcing + CQRS

* Tested with just 20 companies aprox.

What should be next? Getting Ready for Event Sourcing

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• Entities are loaded from the Events already Stored

• Our Main Database is nothing but a Cache (Can we get rid of it? How much does it cost?)

• Watch Marco Pivetta’s Presentation and/or attend his Workshop on Sunday.

Thank you for your attention.