To keep legacy code stable while adding new features, focus on a modular approach and thorough testing. Adding automated tests helps catch issues early and ensures that new updates don’t interfere with existing functionality. This way, we can safely grow the codebase without risking stability.

Introducing new features is essential for growth, but it’s equally important to keep legacy code intact to ensure system stability and continuity. To achieve this, use modular and incremental updates, where new features are developed in isolation from the core legacy code. Implement feature toggles to control the rollout of new functionalities, allowing for selective deployment and easy rollback if issues arise. Rigorous testing, including unit, integration, and regression tests, helps identify potential conflicts. Refactoring legacy code in phases, with an emphasis on backward compatibility, also maintains stability while enabling growth.

Issues with legacy code often arise not only from new features but also from bug fixes or maintenance by developers unfamiliar with the system’s design, coding standards, dependencies, and module interactions. The first step in maintaining legacy code is ensuring comprehensive, up-to-date documentation, making the system human-readable and maintainable. Developers must fully understand the documentation before making changes. A codebase maintenance team or domain experts should review all changes before merging. Additionally, unit tests, functional tests, and load/penetration testing are essential to ensure the legacy system remains intact.

Balancing legacy code maintenance with new feature development requires a thoughtful approach. Incremental refactoring allows for gradual improvements without breaking existing functionality, while automated tests help ensure core features remain intact. Using feature toggles enables safe deployment of new code, and a modular approach isolates changes from legacy systems. Thorough documentation and regular code reviews foster collaboration and understanding, while planning for technical debt helps guide gradual improvements. Implementing continuous integration ensures regular testing, catching issues early. By focusing on these strategies, you can effectively evolve your applications while keeping legacy systems reliable.

There are several ways to add new feature into legacy code without disturbing its functionality: 1. One way is to adopt a modular approach, which allows the development of new features in isolated, well-defined functions, while keeping the legacy code intact. This ensures minimal interference with existing functionality. 2. We can used feature flagging which allow us to enable or disable specific feature without redeploying build on server. This provides flexibility in controlling feature roll outs. 3. Introduce buffers in sprint to refactor legacy code because adding new features without refactoring legacy code might become more risky to address and will eventually slow down systems performance.