Strangling the monolith without stopping the business

The monolith that pays the bills cannot be switched off to be fixed. Every modernization plan that proposes a big-bang rewrite fails for the same reason: the risk is concentrated in a single migration nobody can finance or test.

We build the anti-corruption layer in front, cut the first hot route behind a flag, and run dual-writes with verification rather than hope. Traffic moves one route at a time; the old system is retired only when nothing calls it. Data is migrated with shadow reads and a comparator that runs for weeks, not a weekend cutover that everyone dreads.

What survives

• Five routes moved this quarter, not a five-quarter roadmap.
• Shop keeps trading; settlement keeps settling.
• Rollback is a flag flip, not a restore from backup.

The strangler pattern is not novel — the discipline to do it route by route, with measured verification, is.