What is Rolling Update?

Rolling updates replace instances one at a time (or in small batches). At any point during the update, some instances run the old version and some run the new version. This ensures zero downtime but requires backward compatibility.

Kubernetes performs rolling updates by default: it creates new pods, waits for them to be ready, then terminates old pods. Parameters include maxSurge (extra pods during update) and maxUnavailable (pods that can be down simultaneously).