Terraform Plan PR Commenter

A GitHub Action that posts the output of terraform plan as a comment on Pull Requests. This action helps teams review infrastructure changes directly within their PR workflow, making it easier to catch potential issues before applying Terraform changes.

Features

• Automatically posts formatted Terraform plan output to PR comments
• Updates existing comments instead of creating duplicates
• Optionally skips posting when there are no changes
• Supports custom headers for better organization in multi-environment setups
• Works with binary plan files for accurate change detection
• This GitHub Action is developed using native JavaScript, so it executes way faster compared to an action build using Docker.

Tip

Now you can see what's changing in your infrastructure. But what about how much it will cost?

We developed a GitHub App called CloudBurn that automatically analyzes your Terraform plans and adds cost impact analysis right in your PR comments. Catch expensive decisions before they hit production, not weeks later on your AWS bill.

💰 Two-minute setup

1. Install CloudBurn on the same repository where you use this action
2. Open a PR – This action posts the Terraform plan, then CloudBurn reads it and adds a separate comment with cost analysis

What's included:

• Monthly cost deltas showing exactly how much your changes will increase or decrease your AWS bill
• Real-time pricing from AWS Pricing API based on your infrastructure's region
• Per-resource cost breakdowns with old vs. new monthly costs
• Free forever for 1 repository with unlimited users

Inputs

Input	Description	Required	Default
planfile	Path to the Terraform plan file to post as comment in the Pull Request	Yes	-
terraform-cmd	Command to execute for calling the Terraform binary	No	terraform
working-directory	Directory where the Terraform binary should be called	No	.
token	The GitHub or PAT token to use for posting comments to Pull Requests	No	${{ github.token }}
header	Header to use for the Pull Request comment	No	-
aws-region	The AWS region where the infrastructure changes are being applied (e.g., us-east-1)	No	-

Outputs

Output	Description
markdown	The raw markdown output of the terraform plan command
empty	Whether the terraform plan contains any changes (true/false)

Usage

Example 1: Direct Usage in Workflow

name: Terraform Plan and Comment on PR

on:
  pull_request:
    branches:
      - main

permissions:
  pull-requests: write
  contents: read

jobs:
  plan-and-comment:
    name: Run Terraform Plan and Post PR Comment
    runs-on: ubuntu-latest

    steps:
      - name: Checkout Repository
        uses: actions/checkout@v5

      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v3

      - name: Terraform Init
        run: terraform init

      - name: Terraform Plan
        run: terraform plan -out=tfplan.binary

      # Add this action to your workflow ↓
      - name: Post Terraform Plan Comment in PR
        uses: towardsthecloud/terraform-plan-pr-commenter@v1
        with:
          planfile: tfplan.binary
          aws-region: us-east-1

Example 2: Reusable Workflow Call

Create a reusable workflow in .github/workflows/terraform-plan-comment.yml:

name: Reusable Terraform Plan PR Comment

on:
  workflow_call:
    inputs:
      planfile:
        description: 'Path to the Terraform plan file'
        type: string
        required: true
      working-directory:
        description: 'Terraform working directory'
        type: string
        required: true
      aws-region:
        description: 'AWS Region where resources will be deployed'
        type: string

jobs:
  comment-terraform-plan:
    name: Post Terraform Plan as PR Comment
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
      contents: read

    steps:
      - name: Checkout Repository
        uses: actions/checkout@v5

      - name: Download Plan Artifact
        uses: actions/download-artifact@v5
        with:
          name: terraform-plan-artifact
          path: ${{ inputs.working-directory }}

      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v3

      - name: Terraform Init
        run: terraform init -backend=false
        working-directory: ${{ inputs.working-directory }}

      # Add this action to your workflow ↓
      - name: Post Terraform Plan Comment in PR
        uses: towardsthecloud/terraform-plan-pr-commenter@v1
        with:
          planfile: ${{ inputs.planfile }}
          working-directory: ${{ inputs.working-directory }}
          aws-region: ${{ inputs.aws-region }}

Then call this workflow from your main Terraform workflow:

name: Terraform Plan with Artifact Upload

on:
  pull_request:
    branches:
      - main

jobs:
  plan-infrastructure:
    name: Generate and Upload Terraform Plan
    runs-on: ubuntu-latest

    steps:
      - name: Checkout Repository
        uses: actions/checkout@v5

      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v3

      - name: Terraform Init
        run: terraform init
        working-directory: ./infrastructure

      - name: Terraform Plan
        run: terraform plan -out=tfplan.binary
        working-directory: ./infrastructure

      - name: Upload Plan Artifact
        uses: actions/upload-artifact@v5
        with:
          name: terraform-plan-artifact
          path: ./infrastructure/tfplan.binary
          retention-days: 1

  post-plan-comment:
    needs: plan-infrastructure
    uses: ./.github/workflows/terraform-plan-comment.yml
    with:
      planfile: tfplan.binary
      working-directory: ./infrastructure
      aws-region: us-east-1

Want to test this out first? Check out the AWS Terraform Starter Kit we created. It's a production-ready Terraform template that has a GitHub workflow already configured to use this GitHub Action.

Permissions

This action requires the following permissions:

permissions:
  pull-requests: write  # Required to post comments on PRs
  contents: read        # Required to read repository contents

Documentation

For complete documentation, including advanced configuration options and integration with CloudBurn for cost analysis, visit:

Full Documentation on CloudBurn.io

Author

Maintained by Towards the Cloud