Azure Function - Custom trigger not scaling

Question

I have a function app (Elastic Premium) with a single function that uses a custom trigger implementing IScaleMonitor. The trigger itself works but the scaling logic is seemingly not being executed. When it was first deployed several months ago it scaled as expected, but I recently noticed that it is no longer doing so. I enabled the scale controller logs via the SCALE_CONTROLLER_LOGGING_ENABLED application setting and found a message stating that the trigger type "is unrecognized or has an invalid/incomplete trigger configuration. The scale controller will not be able to directly activate or scale function". This seems to confirm that my IScaleMonitor implementation is effectively being ignored.

I'm unable to find any sort of documentation around that specific message and it's a bit vague. I'm unsure what "invalid/incomplete trigger configuration" would even be referring to but if there's just some configuration I'm missing I would love to know what that is. I'm assuming maybe there are some sort of restrictions that have been placed on what triggers the scale controller will even use. Are custom IScaleMonitor implementations no longer allowed or something? Is there anything I can do to do to get the scale controller to recognize my trigger? I can provide more detailed information on my trigger implementation if needed but given the log message and the fact that it used to work it doesn't feel like a coding problem.

Answer 1

I was able to solve this. For some reason the Runtime Scale Monitoring setting had been set to "Off". I never had to do anything with this setting in the first place so I'm not sure exactly what happened, but setting it to "On" has resolved my issue.

https://learn.microsoft.com/en-us/azure/azure-functions/functions-networking-options#virtual-network-triggers-non-http