Heroku H10 error but web dynos are not crashing

Question

A few hours ago we starting seeing a bunch of H10 errors in our logs and on our Heroku dashboard. Heroku says that H10 errors are due to web dyno crashes. Read more here. The strange part is that our 2 web dynos are running completely fine and not crashing at all.

Here's an example of what I'm seeing in the logs:

2021-08-12T20:50:35.934439+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=POST path="/v1/graphql" host=api.rize.io request_id=abcd-ace1-44e8-99f5-03d38d8eaa5a fwd="1.1.1.1" dyno= connect= service= status=503 bytes= protocol=https

When I search for that request ID, abcd-ace1-44e8-99f5-03d38d8eaa5a in this example, in the logs (as Heroku recommends), nothing shows up except the router error listed above.

I've restarted all the dynos and the issue persists.

Anyone have any idea what could be going on and how we can fix this?

Answer 1

I don't know if this is an answer for other people but we discovered that our DNS settings were not updated to match the changes documented here: https://devcenter.heroku.com/changelog-items/2151

We also needed to re-establish managed SSL certificates for our custom domains.

Our setup has some complications related to proxies we have in front of Heroku though and the fact that of the three custom domains we have configured on the app, only two of them had been migrated, which complicated the debugging of this situation.