It doesn't happen regularly, but I was able to catch it in my debugger:

And then, because of that trailing comma, things further complicate. That error is not even well formatted JSON, which makes it throw DeserializationError, which is how it reaches my code. We can ignore this one, I just needed to bitch about it a little bit.

How do we find why is the "No server available to handle the request" happening? How to mitigate this?

If this is the expected behavior of an overloaded ES cluster, how do we properly handle this error specifically?

Here are the health metrics:

Here's context around the error: