Libvirt Metrics: $host is None in Grafana dashboard if exported values lack dns_name

[Paul Goins]

On one cloud where prometheus-libvirt-exporter has been deployed, records from the exporter look like this in prometheus:

libvirt_up{group="promoagents-juju",instance="[IP REDACTED]:9177",job="prometheus-libvirt-exporter"}

There is no dns_name field.

As the host variable on this dashboard is defined as "label_values(libvirt_up, dns_name)", this results in $host being empty and not being able to use host-based filtering.

[Paul Goins (vultaire)]

This bug extends in impact into the overall dashboard, as a number of fields use expressions such as {dns_name=~"$host"}. Especially when dns_name isn't available on these fields (and thus $host becomes ""), this generates data of limited use - basically everything gets lumped together.

Either we need to always ensure dns_name is present (e.g. stuffing an IP in if DNS names aren't available), or perhaps we need to split on some other identifier?

[Giuseppe Petralia (peppepetra)]

I hit the same today. I upgraded prometheus charm to latest (rev. 24) and scrape jobs had dns_name configured and libvirt dashboard was loading correctly.