Six Rs of Migration
also called 6 Rs, Migration Strategies
The standard menu of options for each application in a migration — rehost, replatform, refactor, repurchase, retire, retain.
Rehost (lift and shift) moves it unchanged: fastest, cheapest, and captures none of the cloud's benefits. Replatform makes small optimisations on the way — managed database, container runtime — and is usually the best return per unit of effort. Refactor rewrites for the target architecture: highest cost, highest ceiling, justified only where the application is strategically important. Repurchase replaces it with SaaS. Retire switches it off, which applies to more of the estate than anyone expects. Retain leaves it where it is, deliberately, with a review date.
The discipline is applying this per application rather than picking one strategy for the portfolio. A migration that refactors everything will not finish; one that rehosts everything arrives in the cloud with the same problems and a higher bill.
Start with retire and repurchase. They are the cheapest outcomes and they are consistently under-applied.