In any long-running software project, architecture is key to scalability, maintainability, and a smooth developer experience. This article dives into the story of a bold architectural shift that transformed a legacy monolith into a sleek, modular system—boosting flexibility, future-proofing the codebase, and making development a whole lot more enjoyable 🚀.

The Challenge: A Legacy Codebase Under Pressure

The legacy project in question had been in operation for approximately four years. Over time, it evolved into a multi-app frontend ecosystem built atop a modern stack—primarily Vue—integrated with REST APIs. While the setup allowed for rapid prototyping and delivery, it also became a bottleneck as the project scaled. The following issues surfaced:

  • Performance Decline: Adding new apps slowed builds and affected performance.
  • Development Experience (DX): With multiple developers working on the same codebase, merge conflicts became a regular occurrence.
  • Bugs: Unexpected bugs surfaced due to intertwined dependencies and a lack of clear boundaries.
  • Scalability: A monolithic structure hindered the team's ability to iterate and grow efficiently.

These challenges made it clear that the project's architecture needed a serious rethink.

Researching Solutions: Modularization with NX monorepo

Determined to address these pain points, I began researching ways to modularize the codebase while adhering to domain-driven design (DDD) principles. The goal was to split the monolithic codebase into self-contained, maintainable modules without sacrificing the integrity of the system.

My research led me to NX, a powerful monorepo tool designed for scalable application development. NX offered:

  • Modularization: Clear separation of apps and libraries into distinct domains.
  • Improved Performance: Incremental builds and caching reduced build times.
  • Enhanced Collaboration: Logical module boundaries reduced merge conflicts and allowed teams to work independently.
  • Modern Tooling: Built-in support for advanced frontend frameworks like Vue and Svelte, combined with testing and linting capabilities.

The Proof of Concept: Bringing the Team on Board

To validate the potential benefits of NX, I created a proof-of-concept (PoC) demonstrating how the legacy codebase could be restructured. The PoC showcased:

  • Clear separation of features into libraries aligned with DDD principles.
  • Incremental builds, which significantly reduced build times.
  • Simplified collaboration, as each team could now focus on their module without affecting others.

Presenting the PoC to the team was a turning point—it got everyone aligned on the vision for a more modular, scalable future.

Making It Happen: The Migration 🚀

Following the approval of the PoC, the team embarked on implementing the NX monorepo structure. The transformation involved:

  • Migration: Gradually moving apps and shared functionality into NX libraries.
  • Refactoring: Aligning components and services with DDD principles.
  • Optimization: Leveraging NX's caching and dependency graph to improve build and test processes.

This change had a huge impact:

  • Improved DX: Developers reported fewer merge conflicts and an overall smoother workflow.
  • Faster Builds: Incremental builds slashed build times significantly ⚡.
  • Scalability: The modular architecture made it easier to onboard new apps and developers.

Key Takeaways

This journey underscores the importance of re-evaluating architectural decisions as projects evolve. By introducing NX into the legacy project, we:

  • Shifted from a monolithic, hard-to-scale structure to a modular, domain-driven architecture.
  • Future-proofed our frontend, making it more maintainable and adaptable.
  • Boosted developer productivity and collaboration in ways that were immediately felt.

For teams struggling with monolithic setups, embracing a monorepo strategy like NX can be a total game-changer. The migration might take effort, but the long-term benefits—for both the codebase and the people working on it—are 100% worth it 💡