# Mutable vs Immutable Infrastructure
## Overview
Infrastructure can be classified as **mutable** or **immutable**, impacting security, maintainability, and reliability.
## Mutable Infrastructure
### Definition
- Can be modified after deployment.
- Updates, patches, and changes are applied in place.
- Common in traditional IT environments and on-premises setups.
### Examples
- Updating a running server with patches.
- Changing configuration files manually.
- Using tools like Ansible, Chef, or Puppet to modify live systems.
### Pros
- Flexibility to apply incremental changes.
- No need to redeploy the entire system for small updates.
- Works well in legacy environments.
### Cons
- Higher risk of **configuration drift**.
- Harder to maintain consistency across environments.
- Security vulnerabilities can persist due to incomplete patching.
## Immutable Infrastructure
### Definition
- Once deployed, infrastructure is never changed.
- Updates require creating a new version and redeploying.
- Old versions are discarded and replaced with new instances.
### Examples
- Deploying new container images instead of updating running containers.
- Using Infrastructure as Code (IaC) tools like Terraform or Pulumi.
- AWS AMIs, Kubernetes pods, and immutable storage models.
### Pros
- Eliminates **configuration drift**, ensuring consistency.
- More **secure**: no ad-hoc changes that introduce vulnerabilities.
- Easier to **rollback** by reverting to a previous version.
- Works well in CI/CD environments with automation.
### Cons
- Requires **full redeployment** for every change.
- Can be **resource-intensive**, requiring new instances instead of patches.
- Learning curve for teams used to mutable infrastructure.
## Security Best Practices
- Prefer **immutable infrastructure** for better consistency and security.
- Use **containerization** and **orchestration** (e.g., Kubernetes) to enforce immutability.
- Automate deployments with **Infrastructure as Code (IaC)**.
- Implement **blue-green deployments** to minimize downtime and risk.
- Regularly audit infrastructure to detect unauthorized changes.
## References
- Infrastructure as Code: [https://www.hashicorp.com/resources/infrastructure-as-code](https://www.hashicorp.com/resources/infrastructure-as-code)
- Kubernetes Best Practices: [https://kubernetes.io/docs/setup/best-practices/](https://kubernetes.io/docs/setup/best-practices/)
- AWS Immutable Infrastructure Guide: [https://aws.amazon.com/builders-library/immutable-infrastructure/](https://aws.amazon.com/builders-library/immutable-infrastructure/)