Direct answer
Heroku does not currently expose an adjustable boot timeout, pre-timeout warning hooks, or a configurable $PORT binding deadline through the platform API, Procfile, or config vars. The router emits R10 when a web dyno does not begin listening on $PORT within roughly 60 seconds, which is the observed platform boot window. You cannot extend that window or add early-warning signals from inside the app, so the reliable fix is to make the web process bind $PORT quickly and move slow startup work elsewhere.
Confirmed behavior versus likely explanation
Confirmed: R10 is platform-enforced. The expected behavior is that the web process binds the port from the $PORT environment variable and listens on 0.0.0.0 during boot. Release-phase tasks and worker dynos are the supported patterns for migrations, cache warmup, and other slow initialization.
Likely explanation: your web dyno is binding a hardcoded port, listening only on 127.0.0.1 or localhost, or running database migrations and dependency loads before the HTTP server starts. Any of these prevents the router from detecting a successful bind inside the 60-second window.
Steps for this case
- Open
Procfile and confirm the web process starts the application server directly, without wrapping it in migration or warmup commands.
- Search the application source for
PORT and replace any hardcoded port with the value from $PORT.
- Configure the server to listen on
0.0.0.0, not 127.0.0.1 or localhost. The Heroku router cannot reach loopback addresses inside the dyno.
- Move database migrations, cache population, and large dependency initialization to Heroku release phase or a separate worker dyno so they do not block the web boot path.
- Redeploy and watch
heroku logs --tail --app <your-app> during a fresh dyno boot for a bind or listen message before any router error.
Platform feature questions
Exposing a configurable boot-timeout flag through the API could break buildpacks and add-ons that assume the 60-second limit, so it should not be treated as an available option. Enhanced startup-phase logging could help, but until Heroku provides it, rely on application-level log lines emitted immediately after the server calls listen.
Verification
heroku logs --tail --app <your-app>
Look for application log lines between dyno creation and the R10 entry. If none appear, the process may be exiting or hanging before it binds the port. Run the app locally with PORT set to confirm it binds successfully before deploying.
Missing diagnostic detail: do you see any application log lines between dyno start and the R10 entry? That determines whether the issue is late binding or an earlier process failure.
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