K8SSAND-1361 ⁃ add /etc/mtab to /proc/mounts symlink to account for the containerd runtime collectd disk monitor

[andrey-dubnik]

Hi,

There is a change when it comes to using the containerd compare to moby runtime as containerd does not create the default symlinks

collectd:df plugin assumes that /etc/mtab is populated accordingly to the collectd logs inside the k8ssadra managed deployment which breaks the disk stats exporter as no mounts are detected

[2022-03-24 01:05:59] setmntent (/etc/mtab): No such file or directory
[2022-03-24 01:05:59] df plugin: cu_mount_getlist failed.

Does this makes sense to update the Dockerfile and add a symlink /etc/mtab -> /proc/mounts so C* disks can be monitored?

┆Issue is synchronized with this Jira Task by Unito
┆friendlyId: K8SSAND-1361
┆priority: Medium

[andrey-dubnik]

I can do a PR if this helps

[emerkle826]

@andrey-dubnik A PR would be welcome. A few notes:

1. Please sign the CLA if you want to contribute code changes (CLA is here https://cla.datastax.com/)
2. If your changes are to Dockerfiles, we are currently maintaining 3 of them in this project:
   • Dockerfile_oss for Cassandra 3.11.x
   • Dockerfile-4_0 for Cassandra 4.0.x
   • Dockerfile-dse-68 for Datastax DSE 6.8.x

[andrey-dubnik]

@emerkle826 PR and CLI are done