Immutable Infrastructure

Immutable infrastructure treats servers as disposable, replacing rather than patching them, which improves security and reliability.

Core principle Instead of updating running servers (mutable), you:

1. Build a new image with updates.
2. Deploy new instances from the image.
3. Route traffic to new instances.
4. Terminate old instances.

Security benefits

• No configuration drift: Servers match their defined state.
• Reduced attack surface: No SSH access needed in production.
• Easier forensics: Compare running image to golden image.
• Faster recovery: Replace compromised instances immediately.
• Consistent patching: Updates apply uniformly.

Implementation patterns

• AMIs/Images: Bake applications into machine images.
• Containers: Package apps in immutable container images.
• Serverless: Functions are inherently immutable.
• GitOps: Infrastructure changes through version control.

Related practices

• Infrastructure as Code (Terraform, CloudFormation).
• CI/CD pipelines for image building.
• Blue-green or canary deployments.
• Container orchestration (Kubernetes).

Challenges

• Longer deployment times (image building).
• Stateful applications require separate data stores.
• Debugging requires centralized logging.
• Initial learning curve for teams.

Zero Trust alignment Immutable infrastructure supports Zero Trust by ensuring systems are always in a known, verified state.