In my thought, To keep software reliable and easy to manage, break it into small parts that can be updated separately. Use automated tests to quickly find problems and ensure new changes don’t cause issues. Also, keep clear documentation to help the team understand the software better. These steps help maintain quality as technology changes.

Maintainance depends heavily on feedback, which means that we need to make feedback as part of our system by design, starting from analytics, to performance and crash reporting ... as 50% of any problem is to detect it in the first place Another important aspect is AB testing and feature flagging, the system should be controlled remotely, as when ever an issue is detected we can close that feature till fixing it to avoid more complicated errors And also when introducing a new feature, applying AB testing and gradual releases will help catch problems early, and comparing performance between multiple flavors of the same feature

Sound design principles ensure the changes are minimal, targeted, not broad (spanning multiple files). The testing pyramid ensures the defects are arrested at the earliest. Keep revisiting the design and coding standards with the team from time to time. Spend time in code review educating the rationale behind changes,standards and its impact.

In my experience, I have found moving away from large monoliths to decoupled modular services has massively aided in creating maintainable and extensible code bases. By following the Gang of Four's rule "program to an interface, not an implementation", it helps keep separation of concerns and removes dependencies of components, enabling new implementations to be added without affecting core business logic. Design patterns like Abstract Factory and Dependency Injection have further supported maintainability by allowing mock dependencies to be injected into services for more robust and automated testing. By keeping components modular, it allows each area of concern or service function to be updated without effecting the rest of the system.

In my experience, a systematic strategy is necessary to preserve software stability in the face of fast change. Using a modular design is a crucial tactic since it enables the updating of individual parts without affecting the system as a whole. Automated testing is essential for identifying problems early and making sure that updates don't interfere with already existing functionality. Additionally, teams are better able to understand and manage the software when a clear and up to date documentation is maintained, which speeds up onboarding and troubleshooting. Software remains dependable, expandable, and easy to use over time when certain procedures are followed.