Troubleshooting Web Start Commands

If you are using custom start commands for your application, such as a standalone binary that runs your application, the output of that command will be logged to /var/log/app.log in the container.  Anything output to stdout or stderr will end up in that file, and it will be truncated to 100MB of total size.

If a request reaches the container and the backend process is not running, a 502 error will be returned and an error logged in /var/log/error.log.  These are some common causes and misconfigurations that can cause those:

• Ensure the process is running.  If the process exits for any reason, it should be restarted.  If the process is unable to stay running, however, no requests may be able to be handled.
• Ensure the process is listening on the correct port defined by the $PORT environment variable.  Requests that are configured to be forwarded to the application will be sent on that port in the application container.
• Ensure the process is not blocked with other requests.  Some applications may get stuck waiting on an external API and block new requests coming in.  You may need to use a tool such as strace to find what the application is stuck on and adjust timeouts for external resources.