What is this feature?
This PR changes the behavior of the $value and .Value variables in alerting templating to be more compatible with Prometheus templating. When a single datasource is used in the alerting rule, these variables will now return the numeric value from the query instead of the evaluation string.
Why do we need this feature?
It makes Grafana templating more compatible with Prometheus templates. In Prometheus, $value returns the numeric value of the query, but in Grafana it's the evaluation string: [ var='A' labels={instance=instance1} value=81.234 ]. This is because in Grafana multiple datasources can be used in the alert rule, and it's not always possible to get a single value.
This change makes Grafana's behavior consistent with Prometheus when a single datasource is used, and in case when multiple datasources are used in the query, it keeps the old behaviour.
Both $value and .Value are not recommended to use (documentation), and it's better to use .Values instead.
This commit changes the state package so that errors encountered while
expanding templates for custom labels and annotations are returned
from the function. This is not used at present, but will be used in the
future as we look at how to offer better feedback to users who don't
have access to logs, for example our customers who use Hosted Grafana.
This commit changes how labels are printed in templates for custom
annotations and labels from map[foo:bar bar:baz] to foo=bar, bar=baz.
Labels are comma separated, and sorted in increasing order.
This commit moves templating from the state package to a sub-package
called template. This sub-package will be the logical package for
future ease-of-use improvements to templating custom annotations
and labels.
Alexander Akhmetov
George Robinson
Serge Zaitsev