Default relabelling to (.*) and $1 ?

[brian-brazil]

Relabelling has a lot of irreducible complexity due to the abundance of different configurations we must allow for, however I think there's some scope for making the syntax a little easier.

I propose that we default the regex to (.*) and the replacement to $1. The effect of this is that copies and setting static labels will both be much easier, both of which are very common uses.

- regex: .*
  replacement: staticvalue
  target_label: myLabel
- source_labels: [src]
  regex: (.*)
  replacement: $1
  target_label: myLabel

would become

- replacement: staticvalue
  target_label: myLabel
- source_labels: [src]
  target_label: myLabel

This is a small bit magic which may cause confusion, but overall I think it'd be a benefit.

@fabxc @beorn7 @juliusv

[fabxc]

That's a good idea 👍

[juliusv]

👍

[beorn7]

👍

[jimmidyson]

Should the default regex actually be (.+) so at least something should be present?

[fabxc]

Then the case for assigning a static value wouldn't work. No source labels are present, so the concatenated value is the empty string, .+ wouldn't mach, and the replacement would be skipped.

Did you see an issue with .* for any particular case?

[jimmidyson]

Good point.

The problem was actually with Kubernetes discovery (of course ;)) where we relabel the metrics path from the service annotation, but this was setting empty path if there was no annotation. I'll update the config there instead.

Closing.

[lock]

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