Strategic Monoliths and Microservices

Make Software Architecture Choices That Maximize Value and Innovation

"[Vernon and Jaskula] provide insights, tools, proven best practices, and architecture styles both from the business and engineering viewpoint. . . . This book deserves to become a must-read for practicing software engineers, executives as well as senior managers."
--Michael Stal, Certified Senior Software Architect, Siemens Technology

Strategic Monoliths and Microservices helps business decision-makers and technical team members clearly understand their strategic problems through collaboration and identify optimal architectural approaches, whether the approach is distributed microservices, well-modularized monoliths, or coarser-grained services partway between the two.

Leading software architecture experts Vaughn Vernon and Tomasz Jaskula show how to make balanced architectural decisions based on need and purpose, rather than hype, so you can promote value and innovation, deliver more evolvable systems, and avoid costly mistakes. Using realistic examples, they show how to construct well-designed monoliths that are maintainable and extensible, and how to gradually redesign and reimplement even the most tangled legacy systems into truly effective microservices.

• Link software architecture planning to business innovation and digital transformation
• Overcome communication problems to promote experimentation and discovery-based innovation
• Master practices that support your value-generating goals and help you invest more strategically
• Compare architectural styles that can lead to versatile, adaptable applications and services
• Recognize when monoliths are your best option and how best to architect, design, and implement them
• Learn when to move monoliths to microservices and how to do it, whether they're modularized or a "Big Ball of Mud"

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Vaughn Vernon, a software developer with over 30 years of experience in a broad range of business domains, is a world-renowned expert in Domain-Driven Design (DDD) and champion of simplicity and Reactive systems. As a consultant and teacher of DDD and Reactive software development, he has helped thousands of developers transform brittle, stagnating, technology-driven systems into innovative, business-driven systems that deliver far more value. The visionary and Chief Architect behind the VLINGO/PLATFORM, he is author of Implementing Domain-Driven Design, Domain-Driven Design Distilled, and Reactive Messaging Patterns with the Actor Model, all published by Addison-Wesley.

Tomasz Jaskula has 20 years of professional experience as a developer, software architect, team leader, trainer, and technical conference speaker. An IDDD Workshop trainer in both French and Polish, he founded Paris Domain-Driven Design and F# user groups. Jaskula's company, Luteceo (luteceo.fr), spreads good software and architecture practices based on Domain-Driven Design and software craftsmanship. He previously worked for many companies in e-commerce, industry, insurance, and finance, gaining deep experience for creating software that delivers clear business value and competitive advantage.

Foreword xiii
Preface xvii
Acknowledgments xxv
About the Authors xxxi

Part I: Transformational Strategic Learning through Experimentation 1

Executive Summary 3

Chapter 1: Business Goals and Digital Transformation 7
Digital Transformation: What Is the Goal? 8
Why Software Goes Wrong 11
Your Enterprise and Conway's Law 18
(Re)Thinking Software Strategy 24
Are Monoliths Bad? 30
Are Microservices Good? 31
Don't Blame Agile 34
Getting Unstuck 36
Summary 37
References 38

Chapter 2: Essential Strategic Learning Tools 39
Making Decisions Early and Late, Right and Wrong 40
Culture and Teams 43
Modules First 51
Deployment Last 55
Everything in Between 57
Where Is Your Spaghetti and How Fast Does It Cook? 70
Strategic Architecture 70
Applying the Tools 72
Summary 75
References 75

Chapter 3: Events-First Experimentation and Discovery 77
Commands and Events 78
Rapid Learning with EventStorming 81
Applying the Tools 92
Summary 99
References 100

Part II: Driving Business Innovation 101

Executive Summary 103

Chapter 4: Reaching Domain-Driven Results 109
Domains and Subdomains 111
Summary 115
References 116

Chapter 5: Contextual Expertise 117
Bounded Context and Ubiquitous Language 117
Core Domain 121
Supporting Subdomains, Generic Subdomains, and Technical Mechanisms 123
Business Capabilities and Contexts 125
Not Too Big, Not Too Small 128
Summary 129
References 130

Chapter 6: Mapping, Failing, and Succeeding--Choose Two 131
Context Mapping 131
Topography Modeling 151
Ways to Fail and Succeed 154
Applying the Tools 158
Summary 163
References 164

Chapter 7: Modeling Domain Concepts 165
Entities 166
Value Objects 167
Aggregates 168
Domain Services 169
Functional Behavior 170
Applying the Tools 173
Summary 173
References 174

Part III: Events-First Architecture 175

Executive Summary 177

Chapter 8: Foundation Architecture 181
Architectural Styles, Patterns, and Decision Drivers 183
Quality Attributes 196
Applying the Tools 206
Summary 207
References 208

Chapter 9: Message- and Event-Driven Architectures 211
Message- and Event-Based REST 216
Event-Driven and Process Management 220
Event Sourcing 223
CQRS 227
Serverless and Function as a Service 229
Applying the Tools 231
Summary 231
References 232

Part IV: The Two Paths for Purposeful Architecture 233

Chapter 10: Building Monoliths Like You Mean It 239
Historical Perspective 241
Right from the Start 244
Right from Wrong 253
Keeping It Right 264
Summary 265
References 266

Chapter 11: Monolith to Microservices Like a Boss 267
Mental Preparation with Resolve 267
Modular Monolith to Microservices 271
Big Ball of Mud Monolith to Microservices 275
Unplugging the Legacy Monolith 286
Summary 287
References 288

Chapter 12: Require Balance, Demand Strategy 289
Balance and Quality Attributes 289
Strategy and Purpose 291
Conclusion 297
References 298

Index 299