tf-drift.yml

name: 'Terraform Configuration Drift Check'

on:
  schedule:
    - cron: '0 4 * * *' # runs nightly at 4 am

#Special permissions required for OIDC authentication
permissions:
  id-token: write
  contents: read
  issues: write

#These environment variables are used by the terraform azure provider to setup OIDD authenticate. 
env:
  ARM_CLIENT_ID: "${{ secrets.AZURE_CLIENT_ID }}"
  ARM_SUBSCRIPTION_ID: "${{ secrets.AZURE_SUBSCRIPTION_ID }}"
  ARM_TENANT_ID: "${{ secrets.AZURE_TENANT_ID }}"

jobs:
  terraform-plan:
    name: 'Terraform Plan'
    runs-on: ubuntu-latest
    environment: production-readonly
    env:
      #this is needed since we are running terraform with read-only permissions
      ARM_SKIP_PROVIDER_REGISTRATION: true
    outputs:
      tfplanExitCode: ${{ steps.tf-plan.outputs.exitcode }}

    steps:
    # Checkout the repository to the GitHub Actions runner
    - name: Checkout
      uses: actions/checkout@v2

    # Install the latest version of the Terraform CLI
    - name: Setup Terraform
      uses: hashicorp/setup-terraform@v1
      with:
        terraform_wrapper: false

    # Initialize a new or existing Terraform working directory by creating initial files, loading any remote state, downloading modules, etc.
    - name: Terraform Init
      run: terraform init

    # Generates an execution plan for Terraform
    # An exit code of 0 indicated no changes, 1 a terraform failure, 2 there are pending changes.
    - name: Terraform Plan
      id: tf-plan
      run: |
        export exitcode=0
        terraform plan -detailed-exitcode -no-color -out tfplan || export exitcode=$?

        echo "::set-output name=exitcode::$exitcode"
        
        if [ $exitcode -eq 1 ]; then
          echo Terraform Plan Failed!
          exit 1
        else 
          exit 0
        fi
        
    # Save plan to artifacts  
    - name: Publish Terraform Plan
      uses: actions/upload-artifact@v2
      with:
        name: tfplan
        path: tfplan
        
    # Create string output of Terraform Plan
    - name: Create String Output
      id: tf-plan-string
      run: |
        TERRAFORM_PLAN=$(terraform show -no-color tfplan)
        echo "## Terraform Plan Output" >> tf.string
        echo "<details><summary>Click to expand</summary>" >> tf.string
        echo "" >> tf.string
        echo '```terraform' >> tf.string
        echo "$TERRAFORM_PLAN" >> tf.string
        echo '```' >> tf.string
        echo "</details>" >> tf.string
        
        SUMMARY=$(cat tf.string)
        SUMMARY="${SUMMARY//'%'/'%25'}"
        SUMMARY="${SUMMARY//$'\n'/'%0A'}"
        SUMMARY="${SUMMARY//$'\r'/'%0D'}"
        
        echo "::set-output name=summary::$SUMMARY"

    # Publish Terraform Plan as task summary
    - name: Publish Terraform Plan to Task Summary
      run: |
        cat tf.string >> $GITHUB_STEP_SUMMARY

    # If changes are detected, create a new issue
    - name: Publish Drift Report
      if: steps.tf-plan.outputs.exitcode == 2
      uses: actions/github-script@v2
      env:
        SUMMARY: "${{ steps.tf-plan-string.outputs.summary }}"
      with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const body = `${process.env.SUMMARY}`;
            github.rest.issues.create({
                owner: context.repo.owner,
                repo: context.repo.repo,
                title: "Terraform Configuration Drift Detected",
                body: body
             })
             
 
    # Mark the workflow as failed if drift detected 
    - name: Error on Failure
      if: steps.tf-plan.outputs.exitcode == 2
      run: exit 1