add rule for legend

[zeitlinger]

It's a good practice to prefix the legend with the instance ID, so that dashboards can show all instances, or only a selected one

[rgeyer]

Thank you for this @zeitlinger.

However, I don't think that this is a hard and fast rule, but more of a guideline. There are absolutely cases where we would want to aggregate all returned series with an average, or sum. Particularly on a stat panel or pie.

There are other cases where we would prefer to aggregate on a different label, such as cluster or a SUO specific label.

If we were to include this as a linting rule, I would advise that we have it emit a warning rather than an error to prevent breaking changes.

As an example, running this on the entire grafana/cloud-onboarding repo, this increases the number of integrations/mixins with failures from 13 to 76.

The 13 which were failing before this change are because of similar changes which broke backward compatibility and/or introduced a rule as an error when it was really a guideline, or simply wasn't thought out thoroughly.

A rule like target-counter-agg, which checks to see that an aggregation function is used, or the legend includes any label would be more applicable, without requiring a specific aggregation, or a specific label.

[v-zhuravlev]

Yes, I agree with @rgeyer , as there are cases when metrics are aggregated by job or cluster, or something else, effectively dropping instance label. Therefore it would be real challenge to enforce such rule. As a general guideline, it would be nice to have this reminder for legend.

[zeitlinger]

Great feedback.
Let's see if we can come up with a better rule:

If global aggregation: skip rule
else if aggregation x (e.g. job, cluster) is used: legend should start with {{x}} -
else: legend should start with {{instance}} -.