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© 2014 SpringOne 2GX. All rights reserved. Do not distribute without permission. DOMAIN-DRIVEN DESIGN / OLIVERGIERKE ƻ OGIERKE@PIVOTAL.IO GRUNDLEGENDES FÜR MICROSERVICES
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4 http://www.infoq.com/minibooks/domain-driven-design-quickly
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Microservices ♥ Domain-Driven Design 5 Slides and video by Michael Plöd.
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Implementing Domain-Driven Design 7
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Value objects 8
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Stringly typed code 9 public class Customer { private Long id; private String firstname, lastname, email; … }
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Stringly typed code 10 public class SomeService { public void createUser(String firstname, String lastname, String email) { … } }
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11 public class Customer { private Long id; private Firstname firstname; private Lastname lastname; private EmailAddress emailAddress; … }
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Value Objects are a PITA to build in some languages. 12
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Still, they’re worth it. 13 See „Power Use of Value Objects in DDD“ by Dan Bergh Johnsson.
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Lombok — putting the spice back into Java. 14
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15 @Value public class Customer { UUID id = UUID.randomUUID(); Firstname firstname; Lastname lastname; EmailAddress email; @Value static class EmailAddress { String value; } }
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AutoValue 16 Project website on GitHub.
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Key opponents: Mapping libraries that need to (de)serialize them. 17
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Entities & Aggregates 18
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Persistence technology VS. Domain model 19
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Challenges with JPA: Value objects as @Entity Flat relationships 20
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21 Order LineItem Product Invoice Customer Payment Address Email
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21 Order LineItem Product Invoice Customer Payment Address Email
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Repositories turn an entity into an aggregate root. 22
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23 Order LineItem Product Invoice Customer Payment Address Email
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Bounded Context 24
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Order LineItem Product Invoice Customer Payment Address
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26 Shipping Accounting Catalog Orders User Registration
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26 Shipping Accounting Catalog Orders User Registration Accounting Payment information Billing Address Shipping Shipping address Customer
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26 Shipping Accounting Catalog Orders User Registration Accounting Payment information Billing Address Shipping Shipping address Customer Product
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Domain-Driven Design & Monoliths 27
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Avoid technologies that get in your way. 28
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How to enforce context boundaries? 29
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What about consistency? 30
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References between Bounded Contexts? 31
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Domain Events 32
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33 Level 0: No events at all
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33 Level 0: No events at all Level 1: Explicit operations
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If you’re calling two setters in a row, you’re missing a concept. 34
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35 Level 0: No events at all Level 1: Explicit operations
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35 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events
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State transitions become domain events. 36
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37 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events
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37 Level 0: No events at all Level 1: Explicit operations Level 2: Some operations as events Level 3: Event Sourcing
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Domain-Driven Design & Microservices 38
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Bounded contexts define system boundaries. 39
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40 Shipping Accounting Catalog Orders User Registration Accounting Payment information Billing Address Shipping Shipping address Customer Product
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41 Shipping Accounting Catalog Orders User Registration Accounting Shipping
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42 Shipping Accounting Catalog Orders User Registration Accounting Shipping HTTP Messaging
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Architecture is less likely to deteriorate as it’s harder to violate boundaries. 43
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Restructuring service boundaries is much harder. 44
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Inter-Service communication becomes remote communication. 45
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Accept and embrace eventual consistency between services. 46
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Domain Events 47
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REST & Messaging 48
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Domain events become state transitions. 49
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Hypermedia for state transition and explicit events. 50
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Thanks! 51