Fly.io Machines Stopping or Not Starting (Auto-Stop)

How to fix it

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

1. 1. Make start and stop settings agree

   Copy steps
   1. In [http_service] set auto_stop_machines = "stop", auto_start_machines = true
   2. Set min_machines_running = 1 to keep one Machine warm (primary region only)
   Did this fix it? Yes No

2. 2. Stop it from exiting immediately

   Copy steps
   1. Add an explicit CMD in the Dockerfile
   2. Run docker run <image> locally; if it exits there, it exits on Fly
   3. Check fly logs for the exit code
   Did this fix it? Yes No

3. 3. Reduce cold start time

   Copy steps
   1. Use auto_stop_machines = "suspend" for faster resume (a few hundred ms vs about 2s)
   2. Be aware suspend causes brief clock skew that can break JWT nbf checks and cron timing; use "stop" if so
   Did this fix it? Yes No

Symptoms

Machines go to stopped state, requests fail or the first request is slow, or Machines never stop.

Why it happens

• auto_stop_machines enabled with auto_start_machines = false
• Private apps not routed through Fly Proxy cannot trigger starts or stops
• Container process exits on its own
• Failed health checks
• min_machines_running at or above Machine count blocks stopping

This guide also covers

• fly.io machine stopped
• fly.io auto stop machines
• fly.io machine not starting
• fly.io cold start

Other Fly.io errors

• Fly.io: The app is not listening on the expected address and will not be reachable by fly-proxy
• Fly.io 502 Bad Gateway
• Fly.io 503 Service Unavailable
• Fly.io Health Checks Failing
• Fly.io Out of Memory (OOM Killed)
• Fly.io Deploy Failed: Waiting for Depot Builder, Registry 401, Too Many Requests
• Fly.io Certificate Not Issuing or Custom Domain Not Working
• How to Cancel Fly.io: Delete an App, Stop Billing and Delete Your Account