Monolith to Microservices

Preface

What You Will Learn
Conventions Used in This Book
O’Reilly Online Learning
How to Contact Us
Acknowledgments

1. Just Enough Microservices
What Are Microservices?
Independent Deployability
Modeled Around a Business Domain
Own Their Own Data
What Advantages Can Microservices Bring?
What Problems Do They Create?
User Interfaces
Technology
Size
And Ownership
The Monolith
The Single Process Monolith
The Distributed Monolith
Third-Party Black-Box Systems
Challenges of Monoliths
Advantages of Monoliths
On Coupling and Cohesion
Cohesion
Coupling
Just Enough Domain-Driven Design
Aggregate
Bounded Context
Mapping Aggregates and Bounded Contexts to Microservices
Further Reading
Summary

2. Planning a Migration
Understanding the Goal
Three Key Questions
Why Might You Choose Microservices?
Improve Team Autonomy
Reduce Time to Market
Scale Cost-Effectively for Load
Improve Robustness
Scale the Number of Developers
Embrace New Technology
When Might Microservices Be a Bad Idea?
Unclear Domain
Startups
Customer-Installed and Managed Software
Not Having a Good Reason!
Trade-Offs
Taking People on the Journey
Changing Organizations
Establishing a Sense of Urgency
Creating the Guiding Coalition
Developing a Vision and Strategy
Communicating the Change Vision
Empowering Employees for Broad-Based Action
Generating Short-Term Wins
Consolidating Gains and Producing More Change
Anchoring New Approaches in the Culture
Importance of Incremental Migration
It’s Production That Counts
Cost of Change
Reversible and Irreversible Decisions
Easier Places to Experiment
So Where Do We Start?
Domain-Driven Design
How Far Do You Have to Go?
Event Storming
Using a Domain Model for Prioritization
A Combined Model
Reorganizing Teams
Shifting Structures
It’s Not One Size Fits All
Making a Change
Changing Skills
How Will You Know if the Transition Is Working?
Having Regular Checkpoints
Quantitative Measures
Qualitative Measures
Avoiding the Sunk Cost Fallacy
Being Open to New Approaches
Summary

3. Splitting the Monolith
To Change the Monolith, or Not?
Cut, Copy, or Reimplement?
Refactoring the Monolith
Migration Patterns
Pattern: Strangler Fig Application
How It Works
Where to Use It
Example: HTTP Reverse Proxy
Data?
Proxy Options
Changing Protocols
Example: FTP
Example: Message Interception
Other Protocols
Other Examples of the Strangler Fig Pattern
Changing Behavior While Migrating Functionality
Pattern: UI Composition
Example: Page Composition
Example: Widget Composition
Example: Micro Frontends
Where to Use It
Pattern: Branch by Abstraction
How It Works
As a Fallback Mechanism
Where to Use It
Pattern: Parallel Run
Example: Comparing Credit Derivative Pricing
Example: Homegate Listings
Verification Techniques
Using Spies
GitHub Scientist
Dark Launching and Canary Releasing
Where to Use It
Pattern: Decorating Collaborator
Example: Loyalty Program
Where to Use It
Pattern: Change Data Capture
Example: Issuing Loyalty Cards
Implementing Change Data Capture
Where to Use It
Summary

4. Decomposing the Database
Pattern: The Shared Database
Coping Patterns
Where to Use It
But It Can’t Be Done!
Pattern: Database View
The Database as a Public Contract
Views to Present
Limitations
Ownership
Where to Use It
Pattern: Database Wrapping Service
Where to Use It
Pattern: Database-as-a-Service Interface
Implementing a Mapping Engine
Compared to Views
Where to Use It
Transferring Ownership
Pattern: Aggregate Exposing Monolith
Pattern: Change Data Ownership
Data Synchronization
Pattern: Synchronize Data in Application
Step 1: Bulk Synchronize Data
Step 2: Synchronize on Write, Read from Old Schema
Step 3: Synchronize on Write, Read from New Schema
Where to Use This Pattern
Where to Use It
Pattern: Tracer Write
Data Synchronization
Example: Orders at Square
Where to Use It
Splitting Apart the Database
Physical Versus Logical Database Separation
Splitting the Database First, or the Code?
Split the Database First
Split the Code First
Split Database and Code Together
So, Which Should I Split First?
Schema Separation Examples
Pattern: Split Table
Where to Use It
Pattern: Move Foreign-Key Relationship to Code
Moving the Join
Data Consistency
Where to Use It
Example: Shared Static Data
Transactions
ACID Transactions
Still ACID, but Lacking Atomicity?
Two-Phase Commits
Distributed Transactions—Just Say No
Sagas
Saga Failure Modes
Implementing Sagas
Sagas Versus Distributed Transactions
Summary

5. Growing Pains
More Services, More Pain
Ownership at Scale
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Breaking Changes
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Reporting
When Might This Problem Occur?
Potential Solutions
Monitoring and Troubleshooting
When Might These Problems Occur?
How Can These Problems Occur?
Potential Solutions
Local Developer Experience
How Can This Problem Show Itself?
When Might This Occur?
Potential Solutions
Running Too Many Things
How Might This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
End-to-End Testing
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Global Versus Local Optimization
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Robustness and Resiliency
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Orphaned Services
How Can This Problem Show Itself?
When Might This Problem Occur?
Potential Solutions
Summary

6. Closing Words

A. Bibliography
B. Pattern Index

Index