Monitoring unique users per day

I’m using the Kong Ingress with the Key Authentication plugin for API authentication.

I’m thinking of recommended ways to monitor unique users per day, for example.

I could do this with logs or potentially prometheus metrics at the API level, but are there any ways to measure this at the Ingress level?

This won’t be possible using metrics. We don’t record consumer-level metrics in prometheus plugin due to the high-cardinality nature of our workloads.
Logging/metrics to an external system is your best option here.

@serain, this looks more like a use case for a dedicated API analytics solution designed for tracking user behaviors and high-cardinality keys like user id: