Heroku R10 Boot Timeout / H20 App Boot Timeout

How to fix it

Try these in order — the most common fix is first.

1. 1. Listen on $PORT first

   Copy steps
   1. Bind the server to process.env.PORT (or $PORT) before doing slow initialization
   2. Never hard-code the port
   Did this fix it? Yes No

2. 2. Do slow work after the port is open

   Copy steps
   1. Connect to databases and warm caches asynchronously
   2. Move migrations to the release phase: release: npm run migrate in the Procfile
   Did this fix it? Yes No

3. 3. Precompile assets at build time

   1. On Rails make sure asset precompilation runs during git push, not at dyno boot
   Did this fix it? Yes No

4. 4. Trim the slug

   Copy steps
   1. Remove unused dependencies and large files
   2. Smaller slugs start faster
   Did this fix it? Yes No

5. 5. Use the boot timeout tool as a stopgap

   Copy steps
   1. Cedar apps can raise the boot timeout temporarily with the Heroku boot timeout tool
   2. It is not a permanent fix
   Did this fix it? Yes No

Symptoms

Logs show Error R10 (Boot timeout) -- Web process failed to bind to $PORT within 60 seconds, or H20 App boot timeout; the dyno restarts in a loop.

Why it happens

• Not listening on $PORT
• Waiting on a database or API before starting to listen
• Heavy startup work or large dependencies
• Rails assets compiled at boot instead of at build
• Very large slug

This guide also covers

• heroku r10 boot timeout
• heroku web process failed to bind to port
• heroku h20 app boot timeout

The same problem in other apps

All not loading, error messages & connection guides →

• DigitalOcean Droplet SSH Connection Refused or Timed Out (DigitalOcean)
• Vercel FUNCTION_INVOCATION_TIMEOUT (504) Error (Vercel)

Other Heroku errors

• Heroku H10 App Crashed Error
• Heroku H12 Request Timeout Error
• Heroku R14 Memory Quota Exceeded Error
• Heroku Application Error Page
• Heroku Build Failed Error
• Heroku Git Push Rejected / Remote Rejected
• Heroku H14 No Web Dynos Running
• Heroku Custom Domain SSL Certificate Not Working