Series Editor Foreword xvii
Preface xxi

Chapter 1: Business Strategy Meets Message-Driven Systems 1

Why Businesses Benefit 2

How Domain-Driven Scenarios Are Solved 3

How Businesses Can Thrive in the Face of Constant, Rapid Change 5

Message-Driven Architecture 6

Loose Coupling 9

Relationship to Reactive Architecture 10

Relation to Monoliths and Microservices 10

Domain-Driven Running Example 12

Modeling Messaging Systems 15

Summary 22

References 23

Chapter 2: Anatomy of Message-Driven Systems 25

Message Broker 26

Synchronous Communication 34

The Structure of Messages 36

Message Categories 39

Serialization, Schemas, and Types in Code 48

Guarantees in Distribution 57

Ordering of Messages 65

Dealing with Duplicates 67

Error Handling 71

Summary 76

References 76

Chapter 3: In-Context Architectures 79

The Purpose of Layers 80

Dependency Inversion 82

Ports and Adapters 89

Generic Layouts and Guided Designs 92

The Four Standard Layers 95

Architecture for the Running Example 106

Summary 107

References 108

Chapter 4: Tactical Building Blocks 109

Value Objects 110

Identities 116

Entities 119

Domain Services 124

Repositories 126

Domain Events 136

Aggregates and Eventual Consistency 147

Summary 162

References 163

Chapter 5: CQRS 165

When Business Software Should Segregate Responsibilities 166

Commands and Queries 170

Command Model and Query Models 175

Model Synchronization 180

Technical Segregation 190

Initializing and Evolving Query Models 195

Eventual Consistency in the User Interface 201

Dos and Donts 203

Summary 205

References 206

Chapter 6: Event Sourcing 207

Your Business as Auditable History 208

Modeling State as Events 211

Event-Sourced Command Model 215

Event Store 222

Comparison of Store Technologies 234

Query Model Projections 246

Processing and Publishing Events 259

Data Deletion 265

Summary 266

References 267

Chapter 7: Long-Running Processes 269

What Is a Process? 270

Message-Driven Processes 278

Choreography 284

Orchestration 290

Correlation of Messages 305

Process as a Domain Model Component 308

Evolution of Long-Running Processes 315

Summary 318

References 319

Chapter 8: Evolution of Messages and Message Streams 321

Purpose and Scope Determine Life Cycle 322

Relation of Data, Serialization, Schemas, and Types 327

Types of Message Changes 332

Adaptation Techniques 338

Evolution of Persistent Message Streams 347

Schema Registries 354

Summary 357

References 358

Chapter 9: Composing Data from Different Sources 359

Global Message Journal 360

Replicating Query Models 370

Synchronous On-Demand Composition 389

The "Right Way" to Compose Query Models 399

Summary 399

References 400

Chapter 10: Message-Driven User Interfaces 401

Frontend Architecture 402

Messaging Technologies and Protocols 406

Executing Commands and Queries 418

Reacting to Events 424

Building Reactive Query Models 428

Client-Side Projections of Change Events 432

Summary 434

References 434

Index 435