mutable infrastructure
also: traditional infrastructure
Infrastructure that is modified in-place by applying updates, patches, and configuration changes directly to running systems rather than being replaced entirely.
Mutable infrastructure means your servers and systems are continuously modified throughout their lifetime. When you need to update software, apply security patches, or change configurations, you log in and make those changes directly on the running system.
For example, you might SSH into a web server and run apt update && apt upgrade to patch it, then restart services. Over time, each server accumulates its own history of modifications, making it unique and potentially difficult to replicate.
This contrasts with immutable infrastructure, where instead of modifying a server, you create a new image with the changes baked in, then replace the old server entirely. Mutable approaches are simpler for small deployments but can lead to configuration drift—where servers gradually diverge and become hard to manage consistently.