Ephemeral disk not mounted when new instance requires reformat of the volume

[Jason Zions]

Each Azure VM is provided with an ephemeral disk, and the cloud-init configuration supplied in the VM image requests the volume be mounted under /mnt. Each new ephemeral disk is formatted for NTFS rather than ext4 or another Linux filesystem. The Azure datasource detects this (in .activate()) and makes sure the disk_setup and mounts modules run. The disk_setup module formats the volume; the mounts module sees that the ephemeral volume is configured to be mounted and it adds the appropriate entry to /etc/fstab. After updating fstab, the mounts volume invokes the "mount -a" command to mount (or unmount) volumes according to fstab. That's how it all works during the initial provisioning of a new VM.

When a VM gets rehosted for any reason (service heal, stop/deallocate and restart), the ephemeral drive provided to the previous instance is lost. A new ephemeral volume is supplied, also formatted ntfs. When the VM is booted, systemd's mnt.mount unit runs and complains about the unmountable ntfs volume that's still in /etc/fstab. The disk_setup module properly formats the volume. However, the mounts module sees the volume is *already* in fstab, sees that it didn't change anything, so it doesn't run "mount -a". The net result: the volume doesn't get mounted.