prometheus check if a metric is present

Question

I have alerts based on a metric which in my case, sometimes, may disappear. Let's say the metric as up(env=prod) and up(env=staging). I have an alert based on the value of this metric. Now, I want to trigger another alert if up(env='staging') is not present. I can sum the metric by env and look at the value but it does not tell me which env is missing.

Answer 1

You can do this with absent(up{env="staging"})