XenServerRescue

Summary
The ability to boot from a rescue image and mount the original virtual machine's disk as a secondary block device. System could have a standard rescue image or use the same base image and the instance being rescued.

Release Note
This functionality will give a user the ability to mount their instance's disk to a temporary "rescue" instance in the event that the instance becomes unbootable.

Rationale
Users need the ability to access their data in the event of the instance becoming unbootable.

User stories
John accidentally wipes a critical configuration file or directory from his instance, which prevents it from booting. John will need the ability to "rescue" his file system by spawning a temporary instance, attaching his original instance's VBD to it and then making any necessary repairs.

Design
Rescue


 * shut down instance
 * spawn temporary instance
 * create temporary VBD
 * plug VBD into temporary instance
 * setup VNC console access to temporary instance

Unrescue


 * unplug VBD
 * destroy temporary VBD
 * destroy temporary instance
 * boot normal instance

UI Changes
n/a

Code Changes
This will live in nova/virt/xenapi.

Migration
n/a