Infrastructure As Code

Overview

Infrastructure defined by hand is infrastructure that drifts, that can't be reviewed, and that can't be reproduced. This skill enforces that all infrastructure is version-controlled code with the same discipline as application code: specs, reviews, tests, and staged deployment.

When to Use

• Before provisioning any cloud resource
• Before modifying production infrastructure
• When investigating a drift between expected and actual infrastructure state

Process

Step 1: Define the desired state first

Write the IaC code that represents the desired state before applying it. Terraform plan / Pulumi preview / CloudFormation change set must be reviewed before apply.

Step 2: Review the plan output

The plan is the diff for infrastructure changes. Review it as carefully as a code diff:

• Are only expected resources being created/modified/destroyed?
• Are any resources being replaced (destroy + create) that should only be modified?
• Are sensitive values being exposed in the plan output?

Step 3: Blast radius analysis

Before applying:

• What is the maximum impact if this change fails?
• Does this change affect production traffic?
• Does this change touch the database, auth system, or network layer?
• Is the rollback procedure documented?

High blast radius changes require explicit approval from a second engineer.

Step 4: State management

• Use remote state with locking (never local state for team environments)
• Never manually modify state files
• Version state file changes
• Test: can you destroy and recreate from scratch?

Step 5: Drift detection

Run drift detection on a schedule. If the actual state diverges from the IaC state, investigate and resolve — don't let drift accumulate.

Step 6: Secrets management

• No secrets in IaC code or state files
• Use: Vault, AWS Secrets Manager, GCP Secret Manager, or similar
• Rotate secrets via IaC, not manually

Step 7: Test the IaC

• Unit tests for modules (Terratest, Pulumi testing)
• Integration tests: deploy to a non-prod environment and verify
• Destroy test: can you tear it down and recreate it?

Step 8: Staged apply

Apply to: development → staging → production. Wait for validation at each stage before proceeding.

Anti-Rationalizations

"It's a small change — I'll do it in the console" Console changes become invisible drift. IaC is the only source of truth. No exceptions.

"We don't need to test infrastructure" Untested IaC fails at the worst moment: during an incident when you need to provision fast.

Verification Requirements

• Plan/preview reviewed before apply
• Blast radius analyzed
• Rollback procedure documented
• State stored remotely with locking
• No secrets in code or state
• Applied to non-prod first
• Drift detection in place