Legacy software feels painful, so the instinct is “rebuild.” Full rewrites fail often because they try to recreate years of edge cases in one project.
Rebuild (or replace modules) when…
- Security or compliance risk is unacceptable.
- Key people are the only ones who understand the system (bus factor).
- New features take months because of architecture constraints.
- Vendor lock-in or dead technology blocks hiring and maintenance.
Do not rewrite when…
- Pain is mostly UI taste, not business outcomes.
- You lack documentation of real workflows.
- Leadership wants a “modern stack” without a migration owner.
Safer modernization paths
- Strangle pattern: new modules around the old core.
- Replace the highest-risk workflow first.
- Add APIs and tests before cosmetic redesigns.
ConaiSoft approaches legacy modernization as incremental product engineering — weekly progress, risk reduced, ownership retained.