Strangler pattern
Replacing a legacy system piece by piece: put a routing layer in front of it, send a growing share of traffic or features to the new system, and retire the old one when nothing uses it. Martin Fowler named it after the strangler fig, a vine that grows around a tree until it replaces it. It avoids a risky big-bang rewrite.
Delivery
In Quorum#
Changing a Service's Stack in a Company starts a migration that runs both versions and moves App Servers over in four steps: 5%, 25%, 50%, then 100% of traffic. Each step costs its share of the migration's Dev Hours (10%, 20%, 30%, 40%), and requests on the new Stack fail 3% of the time until you ship Fix migration bugs. Features on the migrating Service build at half speed.
Read next#
Tech debt, Canary deployment, Feature flag, Blue-green deployment