Feature request for Loki sink: Use event values as labels

[bbreijer]

currently it is only possible to use event values (like namespace) in the layout of a Loki body, it would be very nice to be able to use the event data (link kind, namespace, etc.) in the streamLabels.

I am not familiar with Go, nor do i know how to test this, therefore i did not make a PR.

But looking at the code:
Might this be the addition we are looking for?

In pkg/sinks/loki.go, change:

	eventBody, err := serializeEventWithLayout(l.cfg.Layout, ev)
	if err != nil {
		return err
	}
	timestamp := generateTimestamp()
	a := LokiMsg{
		Streams: []promtailStream{{
			Stream: l.cfg.StreamLabels,
			Values: [][]string{{timestamp, string(eventBody)}},
		}},
	}

into

	eventBody, err := serializeEventWithLayout(l.cfg.Layout, ev)
	if err != nil {
		return err
	}
	streamLabels, err := serializeEventWithLayout(l.cfg.StreamLabels, ev)
	if err != nil {
		return err
	}
	timestamp := generateTimestamp()
	a := LokiMsg{
		Streams: []promtailStream{{
			Stream: string(streamLabels),
			Values: [][]string{{timestamp, string(eventBody)}},
		}},
	}

Could you consider this improvement?

[mi-fabien-cayre]

Would be useful for sure

[mi-fabien-cayre]

Wrote a PR including some tests (I also need this feature to be added)