What Is Immutable Infrastructure? Don't Modify, Rebuild

SSHing into servers to make changes? Experiencing configuration drift? Immutable Infrastructure means you never modify servers — you replace them.

Mutable vs Immutable

Mutable: Create server → SSH → patch → configure → drift over time Immutable: Build image → deploy → update = build new image → replace old

How It Works

1. Build: Create golden image (OS + runtime + app)
2. Deploy: Launch from image
3. Update: Build new image → replace old servers
4. Never SSH!

Containers = Natural Immutable Infrastructure

FROM node:20-alpine
COPY . .
CMD ["node", "server.js"]

Build → immutable image → run → to update: build new image, replace container.

Pets vs Cattle

| Pets | Cattle | |------|--------| | Named servers | Numbered instances | | Repaired when broken | Replaced when broken | | Mutable | Immutable |

Tools

| Tool | Role | |------|------| | Packer | Image building | | Docker | Container images | | Terraform | Infrastructure provisioning | | Kubernetes | Container orchestration |

Best Practices

1. Never SSH — Use logs and monitoring
2. Build images in CI/CD | 3. Centralized logging (ELK, Loki)
3. Blue-Green deploy for easy rollback
4. Version images with tags
5. Separate state — Databases managed independently

Conclusion

Immutable Infrastructure eliminates configuration drift and guarantees identical environments. Containers naturally implement this approach. Don't touch servers — rebuild them.

Learn Immutable Infrastructure on LabLudus.