How do you integrate Infracost with your Terraform CI/CD pipeline to provide cost estimation and implement cost guardrails that prevent deployments exceeding budget thresholds?

# GitHub Actions workflow with Infracost
name: Terraform Cost Check
on: [pull_request]

jobs:
  infracost:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: infracost/actions/setup@v3
        with:
          api-key: ${{ secrets.INFRACOST_API_KEY }}

      # Generate baseline cost from main branch
      - name: Generate Infracost baseline
        run: |
          git checkout main
          terraform init
          infracost breakdown --path . --format json --out-file /tmp/infracost-base.json
          git checkout ${{ github.head_ref }}

      # Generate cost diff for PR
      - name: Generate Infracost diff
        run: |
          terraform init
          infracost diff --path . \
            --compare-to /tmp/infracost-base.json \
            --format json \
            --out-file /tmp/infracost-diff.json

      # Post PR comment
      - name: Post Infracost comment
        run: |
          infracost comment github \
            --path /tmp/infracost-diff.json \
            --repo ${{ github.repository }} \
            --pull-request ${{ github.event.pull_request.number }} \
            --github-token ${{ secrets.GITHUB_TOKEN }} \
            --behavior update

      # Cost guardrail - block if too expensive
      - name: Check cost threshold
        run: |
          DIFF=$(jq '.diffTotalMonthlyCost | tonumber' /tmp/infracost-diff.json)
          if (( $(echo "$DIFF > 5000" | bc -l) )); then
            echo "::error::Cost increase of \$$DIFF/month exceeds \$5000 threshold"
            exit 1
          fi

# infracost-usage.yml for usage-based estimation
version: 0.1
resource_usage:
  aws_s3_bucket.data:
    standard:
      storage_gb: 5000
      monthly_tier_1_requests: 1000000  # PUT/POST/LIST
      monthly_tier_2_requests: 10000000 # GET/SELECT
    glacier:
      storage_gb: 50000
  aws_lambda_function.processor:
    monthly_requests: 5000000
    request_duration_ms: 200