Mount propagation `MountFlags` dependency should be documented

[saad-ali]

This is a...

• Feature Request
• Bug Report

Problem:
Mount propagation for Kubernetes moved to beta in 1.10. Documentation was updated here: #7655

However on some deployments it won't work unless MountFlags=shared is added to /usr/lib/systemd/system/docker.service or MountFlags=slave is removed.

This is documented in the Portworx docs: https://docs.portworx.com/knowledgebase/shared-mount-propogation.html#redhatcentos-configuration-and-shared-mounts

Proposed Solution:

Kubernetes OSS documentation should be updated to explain this and have a similar how-to for different environments.

Page to Update:
https://kubernetes.io/docs/concepts/storage/volumes/#mount-propagation

1.9, 1.10+

/assign @jsafrane

[vladimirvivien]

/assign @vladimirvivien

[vladimirvivien]

Submitted PR #7854

[saad-ali]

Closed with #7854