Kubelet needs to run /bin/mount in its own cgroup.
- When kubelet runs as a systemd service, "systemctl restart kubelet" may kill
all processes in the same cgroup and thus terminate fuse daemons that are
needed for gluster and cephfs mounts.
- When kubelet runs in a docker container, restart of the container kills all
fuse daemons started in the container.
Killing fuse daemons is bad, it basically unmounts volumes from running pods.
This patch runs mount via "systemd-run --scope /bin/mount ...", which makes
sure that any fuse daemons are forked in its own systemd scope (= cgroup) and
they will survive restart of kubelet's systemd service or docker container.
As a downside, each new fuse daemon will run in its own transient systemd
service and systemctl output may be cluttered.
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