Reliable Insights

How do you allow for the keep relabel action halting relabelling for things not kept?

Any targets dropped by the drop relabel action won't be processed by any following relabel actions. The same applies for keep, if it's not kept then it's now gone. In practice this means that a list of actions like

- source_labels: [label]
  regexp: foo
  action: keep
- source_labels: [label]
  regexp: bar
  action: keep

will return nothing, as label cannot be both foo and bar at the same time.

 

You could combine the actions using the regex alternation operator:

- source_labels: [label]
  regexp: foo|bar
  action: keep

This can however get a little unwieldy when you want to apply more intricate business logic across multiple source labels.

 

Another approach would be to set a flag when your criteria is met, and use keep on that:

- source_labels: [label]
  regexp: foo
  target_label: __tmp_keep_me
  replacement: true
- source_labels: [label]
  regexp: bar
  target_label: __tmp_keep_me
  replacement: true
- source_labels: [__tmp_keep_me]
  regex: true
  action: keep

The default replace action only has an effect if it matches, so if label is foo or bar the __tmp_keep_me label ends up with the value true which a keep action can then be predicated on. This pattern can be used with any number of actions.

The __tmp prefix is reserved for user usage in target relabelling, and it is promised that no future Prometheus feature will use this prefix. As is begins with __ it will be discarded with all other metadata before determining the final target labels.

 

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