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How I added carbon tracking to GitHub Actions (and why DevOps should care)

We added carbon linting to Terraform PRs — here's how it works

Most carbon tracking tools are dashboards built for sustainability officers.
They pull three-month-old billing data and produce a PDF. Engineers never see it.

This post is about shifting that left — into the pull request, before
infrastructure is provisioned.

The problem with post-hoc measurement

By the time AWS's Carbon Footprint Tool tells you that your us-east-1
cluster emits twice as much as us-west-2 would have, it has been running
for a quarter. The architecture is locked in, the carbon is burnt.

The only intervention point that changes what gets deployed is the PR.

What GreenOps CLI does

It's a GitHub Action that reads a terraform show -json plan output and
posts a carbon and cost diff directly on the PR.

Here's what a developer sees:

🌿 GreenOps Carbon Analysis

This plan adds +12.94 kg CO2e/month (~$210.24/mo)
💡 2 recommendations found — potential saving: −4.71kg CO2e/month | −$41.61/month

Resource               | Instance   | Region    | CO2e/mo | Cost/mo | Action
aws_instance.api       | m5.xlarge  | us-east-1 | 8.63kg  | $140.16 | → Switch to m6g.xlarge
aws_db_instance.main   | m5.large   | us-east-1 | 4.31kg  | $70.08  | → Switch to m6g.large

Math is MIT-licensed and auditable.
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No AWS credentials required. No outbound network calls from the CLI.
The emission factors are a static JSON file you can read in ten minutes.

How the math works

The emission calculation is a linear interpolation model:

W = W_idle + (W_max - W_idle) × utilisation
energy_kwh = W × PUE × hours / 1000
co2e_g = energy_kwh × grid_intensity_gco2e_per_kwh
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For m5.large in us-east-1 at 50% utilisation this produces
4,313.57g CO2e/month. That value is asserted in engine.test.ts.
You can verify it yourself from factors.json in under five minutes.

The full methodology — every formula, every assumption, every data source —
is in METHODOLOGY.md and MIT-licensed.

Adding it to your workflow 

- name: Generate Terraform Plan
  run: |
    terraform init
    terraform plan -out=tfplan
    terraform show -json tfplan > plan.json

- name: GreenOps Carbon Lint
  uses: omrdev1/greenops-cli@v0
  with:
    plan-file: plan.json
    github-token: ${{ secrets.GITHUB_TOKEN }}
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The Action requires only pull-requests: write. Nothing broader.

Current limitations

  • AWS only. No Azure, no GCP.
  • EC2 and RDS only. No Lambda, no ECS.
  • No embodied carbon.
  • Provider alias regions are not resolved — affected resources are skipped with a known_after_apply reason.

All of the above are tracked in open issues.

Why open source the methodology

Every other tool in this space uses proprietary emission factors.
That doesn't survive a CSRD audit where a compliance officer needs
to trace exactly how a number was produced.

If you disagree with an assumption, open a PR and change it.

→ github.com/omrdev1/greenops-cli

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