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I'm getting a lot of H12 and H15 errors reported on my Heroku metrics dashboard. However they do not appear on the logs at all. The H27 ones do appear, so I know logging in general is working.

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The other clue is that my response time 95th% is terrible at just under 30secs. However, my app is not experiencing any problems I can see at the user end.

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Anybody experienced anything similar, or know how I can investigate without any logs to go on?

Is it even something to worry about or just a red herring?

Further info:

  • I am using 2 standard dynos
  • Running Meteor / NodeJS
  • There are lots of mobile users
Alveoli
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1 Answers1

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This is the best answer I got so far regarding H12 errors on Heroku for my own Meteor app. More from the answer: Meteor, Modulus and secure websockets

It turns out mobile users fall back to XHR instead of using WebSockets. XHR opens long connections with the server that's past 30 sec to listen to any changes. So by design XHR will cause a H12 error on Heroku.

I'd get such error log:

heroku/router:  at=error code=H12 desc="Request timeout" method=POST path="/sockjs/099/ohzgm59n/xhr" host=web.42race.com request_id=d644af4a-8a42-41e0-ac8f-6069358f8e71 fwd="10.181.129.17,118.189.27.195" dyno=web.2 connect=0ms service=30001ms status=503 bytes=0

It seems to be normal and does not affect users.

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Augustine Chua
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