- From Monolith to Modules
- The Refactor That Saved Our CI/CD Pipeline
-
Anatomy of a God-Module
- How Good Intentions Create Architectural Nightmares
- What Is a God-Module?
- Case Study: The Hundred-Plus Registrations
- The Constructor Injection Trap
- The Hidden Cost of Duplicate Instances
- Why Payment Systems Attract This Debt
- Signs Your Codebase Is Suffering
- The NestJS Way: Module Encapsulation
- What’s Next
- The Registry Pattern
- Self-Registering Modules with useFactory
-
Edge Cases and Troubleshooting
- When Things Go Wrong (And How to Fix Them)
- The “Provider Not Registered” Error
- Providers with Partial Capabilities
- Type Casting for Provider-Specific Methods
- Architectural Violations: When Providers Depend on Domain Logic
- Testing Provider Modules in Isolation
- The Accidental Singleton Problem
- What’s Next
-
Migration Strategy
- Zero Downtime, Continuous Delivery, No Big Bang
- The Hybrid Factory: Old and New Together
- The Migration Sequence
- Batching Strategy: How Many at Once?
- The Messy Middle: When Performance Gets Worse
- Handling Test Failures
- Continuing Feature Development During Migration
- Measuring Progress
- The Final Push: Removing Legacy Code
- Timeline Expectations
- What’s Next
-
Scaling to Hundreds of Providers
- Organization, Discoverability, and Long-Term Maintainability
- Folder Structure: Organizing Provider Modules
- My Recommendation
- Naming Conventions That Scale
- The Aggregator Hierarchy
- Selective Imports: Not Everything Needs Everything
- Adding New Providers: The Checklist
- Documentation for Discoverability
- Payment Providers Registry
- Sustainable Engineering
- ADR: Payment Provider Module Architecture
From Monolith to Modules: Refactoring Payment Providers in NestJS
A Real-World Guide to Self-Registering Architectures and Cleaner Code
Tired of god factories and 200-parameter constructors? In one intense week, I turned a payment provider monolith into modular, self-registering NestJS heaven. This book shows you how without losing your mind (mostly).
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About the Book
Learn how to escape monolithic factories in NestJS payment systems.
Based on my real 1-week refactor that turned crushing tech debt into clean, maintainable, modular code.
Includes ready-to-use patterns, templates, and hard-won lessons; plus the personal cost of that sprint (yes, eye twitch included 😅).
Whether you're maintaining a fintech backend or scaling a NestJS app, this book delivers battle-tested strategies to make your code cleaner, more extensible, and truly team-friendly.
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About the Author
Oluwakemi Awosile
Oluwakemi Awosile is a Senior Backend Engineer with over 10 years of experience building scalable fintech systems. Former Tech Lead at Interswitch (Nigeria’s leading payment platform), she now works in a fintech company, specializing in NestJS architecture and refactoring legacy code into maintainable, modular designs.
Her 1-week refactor of a monolithic payment provider system - born from a failing CI/CD pipeline - transformed tech debt into clean, extensible code and inspired this book.
Oluwakemi is passionate about real-world engineering, clean architecture, and sharing lessons from the trenches (including the occasional eye twitch 😅).
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