This adds a new config option to control the maximum number of disk
devices allowed to attach to a single instance, which can be set per
compute host.
The configured maximum is enforced when device names are generated
during server create, rebuild, evacuate, unshelve, live migrate, and
attach volume. When the maximum is exceeded during server create,
rebuild, evacuate, unshelve, or live migrate, the server will go into
ERROR state and the server fault will contain the reason. When the
maximum is exceeded during an attach volume request, the request fails
fast in the API with a 403 error.
The configured maximum on the destination is not enforced before cold
migrate because the maximum is enforced in-place only (the destination
is not checked over RPC). The configured maximum is also not enforced
on shelved offloaded servers because they have no compute host, and the
option is implemented at the nova-compute level.
Part of blueprint conf-max-attach-volumes
Change-Id: Ia9cc1c250483c31f44cdbba4f6342ac8d7fbe92b
melanie witt
bb0906f4f3