Infrastructure approach where servers are never modified after deployment, only replaced. Like using disposable plates instead of washing dishes - throw away and get fresh ones.
Cloud-native applications use immutable infrastructure by creating new server images for every deployment instead of updating existing servers.
Immutable infrastructure is a practice rather than a single service. Across clouds, it’s commonly implemented by building versioned machine images, deploying them to a scale set/instance group/pool, and replacing instances during releases (often with blue/green or rolling updates) instead of patching servers in place.