Comparison
Immutable infrastructurevsIn-place upgrade
Immutable infrastructure
you never patch a running server; you build a new image and replace the instance entirely.
Treating deployed artefacts as read-only and replacing rather than modifying them. It eliminates configuration drift and makes environments reproducible from source. It requires the build and replace cycle to be fast, and it makes stateful nodes the special case that needs a real plan.
Full entry →In-place upgrade
you ran the package upgrade on the running fleet, and now the machines differ from each other by whatever failed halfway.
Modifying running machines rather than replacing them. It is faster and it preserves anything local, which is exactly why it accumulates divergence: every partial failure leaves a machine in a state no image describes. It remains the only option for genuinely long-lived stateful hosts, which is where the discipline of configuration management still earns its keep.
Full entry →