PromQL : compare metric value with its label's value

Question

I have this metric : my_metric{expected_value="123"} 123

Using Prometheus, how can create an alert that triggers when the value differs from the label expected_value's value ?

Answer 1

You cannot. Labels are not supposed to be used in this way, and there are no ways of combination labels and metric values.

Best course of action in this case would be to split your metric into two metrics:

my_metric 123
my_metric_expected_value 123

And introduce alerting rule based on expression:

my_metric != my_metric_expected_value