Custom target labels

[aequitas]

For our use case the TARGETS_LABEL_NAME is currently to limited. I was thinking of contributing support for custom target labels and am curious about your idea about them.

I'm thinking of something like this:

TARGETS=http://localhost:8081/metrics#label_name=value,http://localhost:8082/metrics#label_name=value2|label_name2=value3

Or:

TARGETS=http://localhost:8081/metrics,http://localhost:8082/metrics

LABELS=label_name=value,label_name=value2|label_name2=value3

The second requires less hijacking of the URL notation, but might cause more human error with multiple targets.

[warmans]

Sure, if that would be useful to you feel free to submit a PR. For me the first version looks a bit better. I'm not sure there's any cleaner way to do it with flags/environment variables, they're not really very good for these sorts of structures. But if you need help let me know.