One day recently I woke up to a text from our monitoring service (part of minimal heroku operations tasks) saying our application was down.

Darn it.

Here’s the recreation of my steps in troubleshooting this issue:

  • Login, see that the app is indeed down.
  • Look at newrelic.
  • Look at the logs (papertrail!).
  • Look at the deployment history.
  • Note when the issue started–curses, not when I did a deploy.
  • Open a ticket with heroku (after doing some research). (Love their support.)
  • Double check that the database is good and hasn’t hiccuped.
  • Look at the logs more.
  • Add more dynos, see if that helps.
  • Google the error message.
    •  <app-name> heroku/router: at=info method=POST path=”<url>” host=app.thefoodcorridor.com request_id=8a17648f-2d84-46ea-abf2-5903be894a2c fwd=”216.191.191.58″ dyno=web.3 connect=1ms service=4ms status=503 bytes=477 protocol=https“Notice that the issue is being stated right in the log file (passenger request queue filling up).  Here are sample error messages?
    • <app-name> app/web.3: [ 2017-07-12 14:47:44.3688 65/7f652dffd700 age/Cor/Con/CheckoutSession.cpp:261 ]: [Client 3-281] Returning HTTP 503 due to: Request queue full (configured max. size: 100)
  • Find some posts about the error message.  Here and here.
  • Start researching how to increase request queue size.
  • Talk a walk to clear my head.
  • Think about what external services we call, as that seems to be what might cause the request queue to back up.
  • Read another post that says restarting passenger helped.
  • Restart all dynos.
  • Problem disappears.
  • Look at logs more closely.
  • Last dyno to be restarted was the only problematic dyno.
  • Add comment to ticket about this being the cause.
  • Heroku confirms that the issue may have been the dyno: “sometimes individual dynos will hang and cause errors with 503 responses”
  • Write note to customers about the issue explaining how access to app was affected.
  • Lower number of dynos.
  • Breath a sigh of relief.

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