Server starts giving error responses with no error messages in some unknown circumstances

This happened after the migration to OpenCape, which caused an outage.

All I can see is:

1. The server process stops logging any requests/responses
2. Nginx starts responding with 502s, indicating it's getting some kind of error from the server process

Unfortunately, I did not take a look at what kind of response I got from the server with curl, which could give a clue. If this happens again, that should be the first step.

Related: deploy some mitigations (https://github.com/haskellfoundation/hf-infrastructure/issues/18)