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applyTo: "/*.tf,/*.tfvars"

Terraform Copilot Instructions: Providers, State and Plan Review

Path-specific Copilot instructions for Terraform. They apply through applyTo and leave .github/copilot-instructions.md in place.

Updated for Terraform 1.17, Nov 2026

Do not upgrade dependencies or the framework version unless the task asks.

Stay on the Terraform version in .terraform-version or the CI image. Terraform 1.17 is the current line to write for when CI is already on it. Do not invent a provider argument. Read the locked provider schema. Required version constraints and the lock file are committed. Do not bump a provider because a plan failed on an unknown attribute you guessed.

Project shape

Modules have a small interface: variables, outputs, and resources. A root module wires providers and backends. A child module does not configure a backend. Names describe the resource, not main copied ten times.

State lives in the remote backend the project already uses, with locking. Do not commit terraform.tfstate. A local state file in a PR is a leak.

Changes

plan is the review artifact. apply and destroy are human actions. Do not run them from an agent turn. A -target apply is a last resort with a written reason.

Read the plan JSON or the plan output for replaces, destroys, and IAM changes. A force_new that replaces a database is a high-severity review, not a routine edit.

Security

IAM actions are the verbs the resource needs. Some AWS actions have no resource-level permission and the resource element must be "*". That star is not, by itself, a finding. A finding is a permission wider than the action requires: extra actions, a star on an action that does support resource ARNs, or 0.0.0.0/0 on an admin port.

Secrets are not in .tfvars committed to git and not in outputs. Mark sensitive outputs. A variable default that contains a key is a bug. Use the project's secret manager or a write-only input.

Provider aliases and regions match the environment. Do not point a dev workspace at a prod account to "see if it plans".

Checks

terraform fmt and terraform validate use the project's version. plan runs with the read-only credentials the project documents, in the right workspace. Record the command and whether the plan was applied. The default is not applied.

Mistakes to avoid

• An invented provider field.
• apply or destroy run autonomously.
• Broad IAM or an open admin port.
• A secret in state outputs or committed tfvars.
• A state file committed to the repository.

What changed in this major

Terraform 1.17 plans are the review artifact. Do not invent provider arguments.

Deprecated APIs to never generate

The hashicorp/template provider is deprecated and archived. Replace a template_file data source with the templatefile() function.

Commands

Run terraform fmt and terraform validate. Do not apply.

Example

resource "aws_s3_bucket" "logs" {
  bucket = var.logs_bucket
}

Plan this. Do not apply it from the agent.