Regex for empty string |$^ in dashboards

[Rikkuru]

Installation details
Panel Name: node variable and other
Dashboard Name:os-metrics and other
Scylla-Monitoring Version: master (4.6.1)
Scylla-Version: 5.0.13

Many regex in templates use this expr |$^
For example node variable in os metrics
label_values(node_filesystem_avail_bytes{cluster=~"$cluster|$^", data_center=~"$data_center"}, instance)

so we filter all nodes with selected cluster but also all nodes with missing cluster for some reason

It makes it harder to alter dashboards if your datasource is not exclusively used for scylla metrics and there are nodes without cluster label from other deployments.

Maybe this suffix is not needed ? Why would we want to filter out specific value of label AND also empty value

[amnonh]

The reason for accepting data without a cluster label is to support customers who did not configure the cluster label, we may remove it in a future release as it's a breaking changes