drop directives for useless metrics from node-exporter

[lucabello]

Enhancement Proposal

We should consider whether we want to add some drop directive for metrics that come from node-exporter that are universally accepted as useless.

Examples:

• used_disk_space{device="snapfuse", fstype="fuse.snapfuse", instance="juju-2a486e-1.lxd", mountpoint="/snap/charmed-zookeeper/34"}
• used_disk_space{device="lxcfs", fstype="fuse.lxcfs", instance="juju-2a486e-1.lxd", mountpoint="/var/snap/lxd/common/var/lib/lxcfs"}

Something to consider to add ignored mountpoints directly in node-exporter:

Please add ignored mountpoints in node_exporter parameters like "--collector.filesystem.ignored-mount-points=^/(sys|proc|dev|run)($|/)". Same rule using "node_filesystem_free_bytes" will fire when disk fills for non-root users.

Related issues:

• HostDiskSpace alert doesn't trigger with mountpoints below / grafana-agent-k8s-operator#331