Infrastructure as Code treats infrastructure provisioning and configuration as a
software engineering discipline. Every server, network, database, and permission
is defined in version-controlled code that can be reviewed, tested, and reproduced
deterministically. The principle is simple: if it is not in code, it does not exist.

## Key Points

- **Declarative Definitions**: Describe the desired end state of infrastructure
- **State Management**: Maintain a state file that maps declared resources to
- **Modular Composition**: Package reusable infrastructure components as modules
- **Plan Before Apply**: Always generate and review an execution plan before
- **Drift Detection**: Periodically compare actual infrastructure state against
- **Environment Parity**: Use the same modules with different variable files to
- Store all IaC in version control alongside application code or in a dedicated
- Use remote state with locking. Local state files cause conflicts and data loss
- Never hardcode secrets in IaC files. Reference secret managers or inject at
- Tag every resource with owner, environment, project, and cost center for
- Write automated tests for infrastructure modules using tools like Terratest
- Pin provider and module versions to prevent unexpected behavior from upstream

Infrastructure as Code

Core Philosophy

Infrastructure as Code treats infrastructure provisioning and configuration as a software engineering discipline. Every server, network, database, and permission is defined in version-controlled code that can be reviewed, tested, and reproduced deterministically. The principle is simple: if it is not in code, it does not exist. Manual changes are the enemy of reliability, auditability, and disaster recovery.

Key Techniques

• Declarative Definitions: Describe the desired end state of infrastructure and let the tool determine the steps to achieve it. Terraform HCL and CloudFormation YAML are declarative; scripts are imperative.
• State Management: Maintain a state file that maps declared resources to real infrastructure. Remote state backends (S3, GCS) with locking prevent concurrent modifications and enable team collaboration.
• Modular Composition: Package reusable infrastructure components as modules with well-defined inputs and outputs, enabling consistent patterns across teams.
• Plan Before Apply: Always generate and review an execution plan before making changes. The plan shows exactly what will be created, modified, or destroyed.
• Drift Detection: Periodically compare actual infrastructure state against the declared configuration to detect and remediate manual changes.
• Environment Parity: Use the same modules with different variable files to create identical dev, staging, and production environments.

Best Practices

• Store all IaC in version control alongside application code or in a dedicated infrastructure repository with the same review processes.
• Use remote state with locking. Local state files cause conflicts and data loss in team environments.
• Never hardcode secrets in IaC files. Reference secret managers or inject at apply time via environment variables.
• Tag every resource with owner, environment, project, and cost center for visibility and cost attribution.
• Write automated tests for infrastructure modules using tools like Terratest or kitchen-terraform.
• Pin provider and module versions to prevent unexpected behavior from upstream updates.
• Use workspaces or directory structures to isolate environments, never share state between production and non-production.

Common Patterns

• Hub-and-Spoke Networking: A central networking module provisions VPCs, subnets, and peering; application modules consume network outputs as inputs.
• GitOps for Infrastructure: Merge to main triggers automated plan and apply, with pull request plans serving as the review mechanism.
• Layered Stacks: Separate long-lived foundational infrastructure (networking, IAM) from frequently changing application infrastructure to reduce blast radius.
• Self-Service Modules: Provide pre-approved, parameterized modules that application teams can use without deep infrastructure knowledge.

Anti-Patterns

• ClickOps — making infrastructure changes through cloud console UIs. These changes are untracked, unrepeatable, and invisible to the team.
• Monolithic state files containing hundreds of resources. A single failed apply can block all infrastructure changes.
• Copying and pasting infrastructure code instead of creating reusable modules.
• Ignoring state file security. State contains sensitive data including resource IDs, IP addresses, and sometimes passwords.
• Applying changes without reviewing the plan first. A single misconfiguration can destroy production databases.
• Not implementing proper IAM for the IaC pipeline itself. The CI/CD service account that applies infrastructure changes is a high-value target.