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Industry Best Practices for Terraform Module Libraries

Think of your Terraform module library as a shared internal platform product: it should be versioned, secure by default, governed by policy, documented as an API, and validated continuously. The tools (Checkov, TFLint, etc.) are just the mechanics—the philosophy is about trust, repeatability, and consumer confidence.

  1. Treat Modules as Products

Versioning discipline: Semantic versioning (semver) is the norm. Consumers should be able to pin to a version and trust that breaking changes only come with major bumps.

Backward compatibility: Avoid breaking inputs/outputs unless absolutely necessary. Deprecate gradually with clear documentation.

Documentation as a contract: README, examples, and terraform-docs outputs are part of the “API surface” of your module.

  1. Enforce Consistency and Standards

Naming/tagging conventions: Modules should enforce organizational naming standards, tagging for cost/ownership, and compliance requirements.

Opinionated defaults: Provide secure, compliant defaults (e.g., HTTPS-only storage accounts, diagnostic settings enabled) while still allowing overrides.

Minimal inputs: Don’t expose every possible knob. Abstract complexity into sane defaults and only surface what’s necessary.

  1. Shift-Left Governance

Policy as code: Modules should embed organizational guardrails (e.g., deny public IPs unless explicitly allowed).

Security baked in: Don’t rely on consumers to “remember” to enable encryption, logging, or RBAC. Make it the default.

Automated validation: CI/CD pipelines should validate that modules conform to org-wide standards before publishing.

  1. Lifecycle Management

Promotion flow: Treat modules like software—develop in feature branches, validate in CI, release to a registry (GitHub, Terraform Cloud, or private registry).

Deprecation strategy: Mark old modules as deprecated but keep them available until consumers migrate.

Changelog discipline: Every release should have a clear changelog so consumers know what changed and why.

  1. Collaboration and Transparency

Code ownership: Define CODEOWNERS so changes to modules are reviewed by the right SMEs.

Examples as tests: Example deployments double as documentation and integration tests.

Consumer feedback loop: Encourage teams to open issues/PRs, making the module library a shared asset.

  1. CI/CD Philosophy (with GitHub Actions or similar)

Validation stages:

Syntax/formatting (terraform fmt, validate)

Policy/security checks (best practices, compliance)

Unit/integration tests (using Terratest or example deployments)

Artifact publishing: Treat a tagged release as an immutable artifact. Consumers should never pull from main directly.

Separation of concerns: CI ensures quality of the module; CD (if used) might publish to a registry, but modules themselves don’t “deploy infra” directly.