Heroku Review Apps: Spin‑Up a Fresh Test Environment for Every Pull Request

Problem: Testing Feature Branches in Isolation

When a developer pushes a feature branch, QA and reviewers need a sandbox that mirrors production. Without it, bugs surface only after merge, leading to costly rework and a “works on my machine” cycle. Manual staging setups are time‑consuming and often out of sync with the main app’s dependencies, buildpacks, or config variables.

Thesis: Review Apps Automate a Consistent, Disposable Test Bed

Heroku Review Apps create a temporary dyno stack for every pull request. Each instance inherits the same buildpacks, config vars, and add‑ons as the main app, but runs on its own URL. This gives reviewers instant, isolated feedback and eliminates the need to spin up a separate staging environment.

How Review Apps Work

1. GitHub Integration: A Heroku pipeline is linked to a GitHub repository. When a PR is opened, the integration triggers a pipeline step. 2. Build & Provision: Heroku builds the app from the PR branch, provisions a new review app dyno, and attaches any add‑ons defined in the pipeline. 3. Unique URL: The review app receives a URL like https://-.. 4. Automatic Teardown: When the PR closes, the review app is destroyed unless you configure it to persist.

Setting It Up

Prerequisites: a Heroku account, the heroku CLI installed, and a GitHub repo linked to a Heroku app.

# Verify the pipeline and review‑app settings
heroku pipelines:info --app my‑app

If the pipeline shows Review Apps: Enabled, you’re ready. If not, enable it:

# Add the GitHub integration if missing
heroku pipelines:add --app my‑app --stage production

# Enable review apps on the pipeline
heroku pipelines:review-apps:set --app my‑app --enabled true

Configure environment variables that review apps should inherit:

# Example: set a shared API key
heroku config:set API_KEY=123456 --app my‑app

Optionally, provision a separate database for review apps:

# Add a Postgres add‑on only to review apps
heroku addons:create heroku-postgresql:standard-0 --app my‑app --review-apps

Worked Example: Creating a Review App for a PR

1. Open a PR on GitHub (e.g., branch feature/new‑ui). 2. Heroku automatically builds the PR and creates a review app. Check the PR description – it will contain a link like https://my‑app-feature-new-ui-123.herokuapp.com. 3. Verify the dyno is running:

# List dynos for the review app
heroku ps --app my‑app-feature-new-ui-123

Output will show a web dyno in the web.1 state. If you need to inspect logs:

heroku logs --app my‑app-feature-new-ui-123 --tail

Once the review is complete, close the PR. Heroku automatically tears down the review app, freeing dyno hours and add‑on credits.

Trade‑offs & Limitations

• Cost: Each review app consumes dyno hours and add‑on credits. A team that opens many PRs daily may see a noticeable bump in the bill. Monitor the Resources tab in the Heroku dashboard for each review app.
• State Persistence: Review apps are temporary. Data stored in the database or file system disappears when the app is destroyed. If you need persistent data, seed the database manually or use a separate add‑on that persists beyond the review app’s lifecycle.
• Build Failures: Because review apps share the same buildpacks and config as the main app, a misconfigured build (e.g., missing environment variables) will cause all review instances to fail. Ensure your CI pipeline validates the build before a review app is provisioned.

Actionable Next Steps

1. Enable Review Apps on your Heroku pipeline (if not already). heroku pipelines:review-apps:set --app <app> --enabled true
2. Configure shared config vars and optional add‑ons for review apps.
3. Educate your team: when a PR opens, the review app URL appears in the PR description. Use this URL for automated tests, manual QA, or stakeholder demos.
4. Set up billing alerts: heroku addons:info heroku-postgresql --app <app> and monitor dyno usage via the dashboard.
5. Automate cleanup if you prefer manual control: heroku review-apps:destroy --app <review‑app‑name> after the PR is merged.

With Review Apps, every pull request gets its own isolated, production‑like environment, cutting down on merge conflicts and speeding up feedback loops. The trade‑off is a modest increase in dyno consumption, but the payoff in developer velocity and QA confidence is substantial.