Fly.io Deployment

---

name: fly-deployment description: Deep knowledge about deploying applications to Fly.io (MicroVMs, Docker). type: transform tier: library domain: deploy trigger: "when deploying to Fly.io"

Context

Deploying {{project_name}} ({{project_type}}) to Fly.io. You will follow a strict 6-phase Deployment Lifecycle Contract.

Instructions

Execute the following phases in order:

Phase 1: Authentication

1. Ensure the FLY_API_TOKEN environment variable is set to a valid token.
2. If running locally, authenticate interactively with fly auth login. For automated agents, ensure the token is provided.
3. Validate by running fly auth whoami.

Phase 2: Build

1. Prepare the artifacts for deployment.
2. Fly.io uses a fly.toml configuration file and a Dockerfile (or buildpacks) to build your application on their builders.
3. Ensure the Dockerfile builds successfully locally (docker build .) to catch any errors early.
4. If your project requires generating static assets before pushing, run your framework's build command (e.g., npm run build).

Phase 3: Install / Provisioning

1. Ensure the target Fly.io application exists. If not, initialize it using fly launch --no-deploy.
2. Check the fly.toml file to ensure the application name, regions, and environment variables are correctly configured.
3. Ensure required secrets are set using fly secrets set KEY=value.
4. If your application requires a database (Postgres, Redis), ensure it's provisioned via fly postgres create or fly redis create and attached to the app.

Phase 4: Deploy

1. Ship the artifact to Fly.io.
2. Run fly deploy to build and deploy your application. You can append --remote-only to force the build on Fly's remote builders.
3. Use --detach if you do not want to wait for health checks to pass in the foreground (not recommended for automated agents unless monitoring separately).

Phase 5: Checking

1. Verify the deployment was successful.
2. Run fly status to check the application's instances and their health status.
3. Retrieve the public URL using fly info and use curl -sSf <URL> to ensure the application returns a 200 OK status code.
4. Check logs via fly logs if the deployment fails or instances are crashing.

Phase 6: Update / Rollback

1. If Phase 5 fails, immediately initiate a rollback.
2. Fly.io supports rolling back to previous deployments. Identify the previous image or release version and run fly deploy -i <previous-image-ref>.
3. Note the failure in the progress log.

Validation

• [ ] Fly.io authentication (fly auth whoami) succeeds.
• [ ] Build succeeds (locally or remote).
• [ ] Application instances are running (fly status).
• [ ] Health check (curl) returns 200 OK.