Hi - I was wondering if it's possible to produce a side output stream from a Sink? I understand this isn't supported out-of-the-box for Sink functions but is anyone aware of any patterns/workarounds to achieve this? Use case: we would like to track events that produce an error in the Sink by sending details to a separate sink.

This is not possible with the off-the-shelf sinks. If you are using a custom sink then you could potentially implement something, but I agree generally it would be nice to have a standardised error output mechanism for sinks. I did look into implementing side output on sinks before, but was not a trivial change. If someone is willing to put together a FLIP I would be interested in contributing.