Guardrails / terraform

Terraform modules are pinned

terraform/modules-pinned@v1

Every module a Terraform root pulls from a registry or a git URL names a version, so the same commit always resolves to the same module code.

Id	terraform/modules-pinned
Version	v1
Category	terraform
Default severity	error
Interpreter	python3
Timeout	30 seconds
Violations tolerated	0
Collects	terraform

Collectors

This guardrail doesn't gather anything itself. It relies on the collectors below, which the CLI runs once per build before any check, and reads what they found from GUARDRAIL_FACTS. If a collector collects nothing, this guardrail is skipped, not failed.

Collector	Gathers	Inputs it is given
terraform	The Terraform configuration in the checkout: every root directory holding .tf files, the backend it stores state in, the providers and modules it takes on and how tightly they are pinned, the resources it declares, the variables it takes, the lock file that resolves it, and any state file left in the tree. Everything is read from the files themselves, so it works on a runner with no Terraform installed. When the terraform CLI is there, the versions an initialised root has already resolved are added.	none

The inputs above are this guardrail's own inputs, passed straight through to the collector. Setting one in buildnote.json changes what is collected, and two guardrails configured the same way share a single collection.

Configuration

{
  "guardrails": {
      "failOn": "error",
      "checks": [
          {
              "use": "terraform/modules-pinned@v1",
              "severity": "error",
              "with": {
                  "allowMovableRefs": "false"
              },
              "exemptions": []
          }
      ]
  }
}

Inputs

Input	Description	Default	Environment variable
allowMovableRefs	Whether a git source pinned to a tag or branch instead of a commit SHA counts as pinned. false requires a 40 character SHA, the only ref nobody can move.	false	GUARDRAIL_INPUT_ALLOWMOVABLEREFS

How to fix

Pin the modules named in the violations. For a registry source, pin with version:

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.8.1"
}

For a git source, pin with a ref in the URL. A tag isn't enough, because a tag can move:

module "vpc" {
  source = "git::https://github.com/company/terraform-vpc.git?ref=6f3a1c2d9b8e4f7a0c5d2e1b3a4f5c6d7e8f9a0b"
}

With an unpinned module, the plan you reviewed and the plan that was applied can come from different code. A module in this repository, referenced with a relative source, is already pinned by the commit and isn't checked.

More in terraform

• terraform/no-plaintext-secrets. Every Terraform variable named like a credential declares sensitive = true.
• terraform/providers-pinned. Every provider a live Terraform root requires is pinned to one exact version, and the lock file that resolves them is committed.
• terraform/remote-state. Every live Terraform root stores its state in a remote backend, and no state file is left in the checkout.
• terraform/state-encrypted. Every live Terraform root declares an encrypted backend, so its state isn't stored in the clear in its bucket.
• terraform/state-locking. Every live Terraform root declares state locking, so two applies cannot write the same state at once.

All 6 terraform guardrails