While the idea of starting fresh can be tempting, a complete rewrite comes with significant risks and challenges. Understanding when and how to approach a rewrite is critical for success, as the decision can have long-lasting implications for the organization.

The Risks of a Full Rewrite

A full rewrite is both expensive and risky. One of the most common mistakes is underestimating the scope of the project. Rewriting a system often takes far longer than anticipated, making careful scoping and planning essential before any work begins. Without thoughtful design, a new system can inherit the same structural issues as the old one, leading to repeated mistakes.

Another risk arises from not migrating to the new system completely and ending up operating multiple systems in parallel. Running old and new systems simultaneously can create operational complexity and additional costs. In some cases, organizations even end up managing multiple versions or rewrites in parallel, which further compounds the challenge. There is also the risk of never finishing the project. Large rewrites can stall indefinitely if priorities shift or resources are depleted, leaving organizations with partially completed systems that are difficult to maintain.

Because of these challenges, a complete rewrite should be avoided unless absolutely necessary. In many cases, refactoring or incremental rewrites are safer and more effective strategies. Incremental rewrites allow old components to be gradually replaced and deployed, significantly reducing the risk of disruption while modernizing the system.

Incremental or Modular Rewrites

Incremental or modular rewrites offer a more controlled approach. Instead of attempting to replace the entire system at once, organizations gradually rewrite old components and deploy them in stages. This strategy minimizes risk and allows teams to respond to challenges as they arise.

The process begins with a comprehensive feature implementation and deployment plan developed in collaboration with key stakeholders and software developers. Each feature should be documented, and all new feature requests frozen to avoid scope creep. Resources should be allocated carefully to ensure smooth execution.

Rewriting and deploying one module at a time is recommended, with new features controlled through feature flags. These flags allow teams to enable features gradually, initially for a limited environment or user group, and then expand deployment step by step across all environments and modules.

It is essential to define a clear schedule for turning feature flags on and off, ensuring that temporary toggles do not linger indefinitely. Once a feature has been validated in production, the old implementation should be removed from the codebase to avoid unnecessary complexity and technical debt. Sticking to the schedule also helps prevent situations where two parallel systems coexist longer than intended, which can lead to increased maintenance overhead and inconsistencies in behaviour.

Testing is critical throughout this process and should include automated tests, regression tests, and user acceptance testing. Running a backup of the old system is advisable, but it is equally important to have a clear plan for decommissioning the legacy system entirely.

This approach reduces risk, allows real-world testing in production-like conditions, and provides a fallback if problems occur. Incremental rewrites help organizations modernize their software in a manageable, systematic way without jeopardizing ongoing operations.

Conclusion

Rewriting software from scratch is among the most complex projects a software team can undertake. While it can deliver significant long-term benefits, the costs and risks involved are substantial. Incremental or modular strategies are generally safer, enabling organizations to modernize their systems gradually while maintaining operational continuity. A complete rewrite should only be pursued when a system is truly beyond repair, and even then, it requires meticulous planning, disciplined execution, and robust risk management to ensure success.

If you would rather have a professional team do the heavy lifting for you, or have any questions please feel free to contact Team Brookvale here.