From Chaos to Cohesion: Migrating Multiple Repositories to a Monolithic Architecture

At Tasq.io, I led a challenging yet rewarding initiative: transitioning several loosely connected repositories into a cohesive monolithic repository. This task, however, wasn’t just about merging code; it also involved addressing fundamental issues within each repo, from missing unit tests to inconsistent code quality. Through a structured migration process and the introduction of automated tools like Black, Ruff, and Sourcery, I transformed our development workflow into one that’s efficient, maintainable, and scalable.

Why Move to a Monolith?

Managing multiple repositories can complicate code management and collaboration, leading to issues like:

• Code Duplication: Shared logic is often duplicated across projects.
• Dependency Management: Each repository requires separate dependency tracking.
• Deployment Inefficiencies: CI/CD pipelines become challenging to maintain across repos.

Moving to a monolithic repo using Polylith’s modular approach presented a solution that allowed us to consolidate shared code, simplify dependency handling, and centralize deployment.

The Initial Challenges

The transition wasn’t without hurdles. The codebases lacked essential elements like:

1. Unit Tests: A lack of unit tests made it challenging to ensure that functionality remained intact during the migration.
2. Code Quality: Without standardized linting or formatting, code readability and maintainability were inconsistent.
3. Code Duplication: Shared functions and utilities were duplicated across repositories, making updates complex and error-prone.

These challenges meant that, in addition to migrating code, I had to improve code quality and enforce new standards across the monolith.

Using Polylith’s Approach to Structure the Monolith

The Polylith architectural style helped us structure the monolith in a way that balanced modularity with code reuse:

• Components: Independent, reusable modules containing business logic.
• Bases: Containers that allow components to interact and function as coherent applications.
• Projects: Representing top-level applications, these projects leveraged shared components without redundant code.

Building with Pants for Scalability

Using Pants build enabled us to manage the growing codebase efficiently:

• Selective Builds: Pants allows building only the changed code, significantly reducing build times.
• Dependency Isolation: With Pants, we could isolate dependencies per module, avoiding version conflicts and unnecessary bloat.
• Optimized Testing: By testing only impacted modules, Pants helped streamline the CI process, saving time and resources.

Improving Code Quality with Automated Tools

After the migration, I introduced several automated tools to improve code quality, enforce consistency, and reduce technical debt:

• Black: An automatic code formatter that enforced a unified style across the monolith, making the codebase cleaner and more readable.
• Ruff: A fast, Python linter that ensured our code adhered to best practices, catching potential bugs and enforcing style consistency.
• Sourcery: A tool to detect and remove code smells, simplify logic, and provide intelligent code suggestions, Sourcery helped maintain cleaner and more efficient code.

With these tools, I configured a unified GitHub workflow for automated linting and formatting, ensuring code quality checks were part of our CI/CD pipeline.

Incrementally Adding Unit Tests

The lack of unit tests in the initial repos posed a risk to functionality during migration. Here’s how I approached testing:

• Module-by-Module Testing: After migrating each repository, I added unit tests for its core functions, focusing on critical components first.
• Automation: Unit tests were integrated into the GitHub workflow, enabling automated testing for each pull request.
• Code Coverage Tracking: I set up code coverage tracking to measure test completeness and ensure no gaps.

With these steps, we ensured the monolithic repo was more reliable and resilient.

Results and Key Takeaways

The transition to a monolith not only streamlined our development process but also brought improvements in code quality and efficiency. Here are the key takeaways:

• Improved Collaboration: A single repository reduced the complexity of collaborating across projects.
• Enhanced Code Quality: Automated tools like Black, Ruff, and Sourcery maintained consistent, high-quality code.
• Reduced Redundancy: Consolidating duplicated code reduced technical debt and improved maintainability.
• Optimized Build and Testing: With Pants, our CI/CD process became more efficient, reducing time spent on builds and tests.

Migrating to a monolithic repository is more than a simple structural change. It’s an opportunity to improve processes, enhance collaboration, and set up a robust framework for sustainable growth. By combining Polylith’s modular approach, Pants build, and automated quality tools, I transformed our codebase into a cohesive, maintainable monolith. This journey required both technical and organizational changes, but the results were well worth the effort.