The health check path answers with an error

The health check path does not exist in the app, or it answers with a status of 400 or more.

What you see

Deploy log

==> Deploy failed: health check timed out after 120s: GET /healthz returned HTTP 404

The deploy gets the status deploy_failed. The previous deploy continues to answer.

The path of the health check (--health) does not exist in the app. Or the app answers with a status code of 400 or more.

Terminal

ferry update NAME --health /path   # correct the path
ferry update NAME --health ""      # or remove the path

The health check times out

Ferry cannot connect to the port of the new instance. The app listens on the wrong address or port.

The app crashes

The app stopped with an error while Ferry waited for its health check.