Does PromQL offer a way to filter metrics by comparing one label value to another label value for the same metric? Like (hypothetical, is invalid syntax) some_metric{label_a!=label_b}.

I’m trying to find metrics by the relative value of two different labels on the same metric.

Consider some metric replication_lag with labels source_region and region. The source_region is where the service is pulling replication data from, the region is the service instance’s location.

I want to find replication_lag only for cross region replication links, those where source_region != region. In other words I want to filter out those metrics where region == source_region.

Is there any way to do this in PromQL?

I’ve been unable to find any way by which a filter on one label’s value can use the value of another label to perform a simple set-filtering operation.

Another way to do this would be to label-match two sets replication_lag{some_unique_key,region} and replication_lag{some_unique_key,source_region} – but this would require a means to label-match on an inequality condition for region and some_region i.e. perform an anti-join, which PromQL also does not appear to support.

The unless operator looks like it’s close, but it requires exactly matching label sets. I need to preserve both region and source_region in the resulting set.