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[melanie witt <1897950@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

This is a bug to track the addition of a note to the config option help
for [compute]max_disk_devices_to_attach. An issue was raised downstream
[1] around the fact that setting this option to 0 will cause instances
not to boot because they will be allowed 0 disk devices.

The CONF.max_disk_devices_to_attach option controls the maximum number
of disk devices allowed to attach to an instance. If it is set to 0, it
will literally allow no disk device for instances, preventing them from
being able to boot.

There doesn't appear to be any way to disallow particular values
in a oslo.config IntOpt other than the min/max values. Here we need the
min value to be -1 to represent unlimited. There is a 'choices' kwarg
available but that is only for enumerating valid values and we need to
allow any integer >= 1 as well. Finally, there doesn't seem to be a
good way to validate this option setting as -1 or >= 1 because it's a
nova-compute config option and our choices there are likely: prevent
nova-compute from starting because of value 0 or log a WARNING about
it, both of which seem like they might be overkill. So, highlighting
the behavior of value 0 in the documentation might be the best way to
handle the issue.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1801931

** Affects: nova
     Importance: Low
     Assignee: melanie witt (melwitt)
         Status: In Progress

** Affects: nova/stein
     Importance: Undecided
         Status: New

** Affects: nova/train
     Importance: Undecided
         Status: New

** Affects: nova/ussuri
     Importance: Undecided
         Status: New

** Affects: nova/victoria
     Importance: Undecided
         Status: New


** Tags: doc

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https://bugs.launchpad.net/bugs/1897950

Title:
  doc: setting [compute]max_disk_devices_to_attach = 0 prevents
  instances from booting

Status in OpenStack Compute (nova):
  In Progress
Status in OpenStack Compute (nova) stein series:
  New
Status in OpenStack Compute (nova) train series:
  New
Status in OpenStack Compute (nova) ussuri series:
  New
Status in OpenStack Compute (nova) victoria series:
  New

Bug description:
  This is a bug to track the addition of a note to the config option
  help for [compute]max_disk_devices_to_attach. An issue was raised
  downstream [1] around the fact that setting this option to 0 will
  cause instances not to boot because they will be allowed 0 disk
  devices.

  The CONF.max_disk_devices_to_attach option controls the maximum number
  of disk devices allowed to attach to an instance. If it is set to 0, it
  will literally allow no disk device for instances, preventing them from
  being able to boot.

  There doesn't appear to be any way to disallow particular values
  in a oslo.config IntOpt other than the min/max values. Here we need the
  min value to be -1 to represent unlimited. There is a 'choices' kwarg
  available but that is only for enumerating valid values and we need to
  allow any integer >= 1 as well. Finally, there doesn't seem to be a
  good way to validate this option setting as -1 or >= 1 because it's a
  nova-compute config option and our choices there are likely: prevent
  nova-compute from starting because of value 0 or log a WARNING about
  it, both of which seem like they might be overkill. So, highlighting
  the behavior of value 0 in the documentation might be the best way to
  handle the issue.

  [1] https://bugzilla.redhat.com/show_bug.cgi?id=1801931

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