🔸 TL;DR
Legacy code is not a monster to duct-tape or rewrite from scratch.
The safest path is usually the Strangler Fig pattern: you rewrite by steps, slowly growing new code around the old system and replacing parts one by one 🌱➡️🌳
🔸 THE TWO EXTREMES TO AVOID
▪️ “Dirty patch” in duct-tape mode: NO ❌
Quick hacks, global flags, side effects everywhere… you ship faster today but create a future time bomb. More bugs, more fear to touch the code, and zero learning for the team.
▪️ “Let’s rewrite everything”: NO ❌
The big-bang rewrite is seductive… and dangerous. You lose hidden business rules, underestimate complexity, and need years before reaching feature parity. Meanwhile, the old system still runs in production. Double cost, double risk.
🔸 WHAT IS THE STRANGLER FIG PATTERN? 🌳
The Strangler Fig is a tree that grows around another tree, slowly replacing it:
▪️ You start by building new pieces around the legacy system
▪️ You route a small part of the traffic to the new code
▪️ You migrate feature by feature
▪️ Over time, the old system becomes thinner… until it can be safely removed
Instead of one giant risky rewrite, you get many small controlled changes.
🔸 PRACTICAL STEPS TO APPLY IT
▪️ Identify seams: find places where you can intercept calls (API gateway, façade, adapter).
▪️ Wrap the legacy: add an interface / façade that becomes your new entry point 🧱.
▪️ Migrate feature by feature: move one endpoint, one use case, or one module at a time.
▪️ Run both in parallel: compare results, add monitoring & logs to detect regressions 📊.
▪️ Decommission safely: when a legacy part has 0 traffic, remove it. Celebrate, repeat 🎉.
🔸 KEY TAKEAWAYS
▪️ Legacy code is valuable: it runs real business and encodes years of decisions.
▪️ Avoid both duct-tape patches and heroic rewrites as default strategy.
▪️ Use the Strangler Fig pattern to evolve safely: small steps, real feedback, less drama.
▪️ Invest in tests, monitoring, and clear boundaries to make each step reversible.
#legacycode #refactoring #stranglerfigpattern #softwarearchitecture #cleancode #javadeveloper #springboot #microservices #techlead #softwareengineering
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