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Playbook · Change · 6 steps
Migrating a legacy system
Replace the plane while it is flying — without dropping passengers.
“…the single worst strategic mistake that any software company can make: They decided to rewrite the code from scratch.”
- 1Chesterton's FenceFind out why the odd parts exist before removing them.Don't remove a fence until you know why it was put up.Open
- 2The Map Is Not the TerritoryVerify the documented integrations against real traffic.Every diagram, model, and dashboard is a simplification. The running system is the truth.Open
- 3Strangler FigWhere can we intercept traffic and move the first thin slice?Replace a legacy system gradually by growing the new one around it until the old one can be removed.Open
- 4Data GravityPlan the data migration as the critical path.Data attracts applications, services, and more data — and the bigger it gets, the harder it is to move.Open
- 5Gall's LawProve a small, working path end to end before scaling out.A complex system that works evolved from a simple system that worked.Open
- 6Sunk Cost FallacyReview progress on evidence, not on money already spent.Past investment is gone either way. Decide based on future costs and benefits only.Open