Immutable infrastructure is a paradigm where servers are never modified after deployment. Instead of patching or configuring running systems, new machine images are built with all necessary updates and deployed as replacements. This approach eliminates configuration drift and makes deployments predictable and repeatable.
Building an Immutable Pipeline
Tools like Packer create machine images with all required software and configuration baked in. These images are tested in a staging environment and then promoted to production through a blue-green or rolling deployment strategy. If an issue is discovered, rollback is simply a matter of redeploying the previous known-good image.
Container-based deployments are inherently immutable since container images are rebuilt rather than modified. This aligns naturally with continuous delivery pipelines where every commit produces a new artifact that flows through testing stages before reaching production.
The shift to immutable infrastructure requires changes in operational practices. Log aggregation and external monitoring become mandatory since you cannot SSH into a server to troubleshoot. Configuration must be externalized through environment variables or configuration services rather than managed through configuration management tools running on the server.