You incrementally replace parts of a monolith with new services. Old code is strangled (removed) as new services take over. Each step is shippable and reversible. It is the safe way to split a monolith.

Use the saga pattern: each service does its part and publishes an event. If a step fails, compensating events undo prior steps. You accept eventual consistency instead of ACID transactions.

A pattern that stops a service from calling a failing downstream service. It trips after N failures, fast-fails subsequent calls, and resets when the downstream recovers. It prevents cascading failures.