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[Chris Friesen <chris.friesen@xxxxxxxxxxxxx>]

Public bug reported:

When doing a rebuild the assumption throughout the code is that we are
not changing the resources consumed by the guest (that is what a resize
is for).  The complication here is that there are a number of image
properties which might affect the instance resource consumption (in
conjunction with a suitable flavor):

hw_numa_nodes=X
hw_numa_cpus.X=Y
hw_numa_mem.X=Y
hw_mem_page_size=X
hw_cpu_thread_policy=X
hw_cpu_policy=X

Due to the assumptions made in the rest of the code, we need to add a
check to ensure that on a rebuild the above image properties do not
differ between the old and new images.


While they might look suspicious, I think that the following image properties *should* be allowed to differ, since they only affect the topology seen by the guest:

hw_cpu_threads
hw_cpu_cores
hw_cpu_sockets
hw_cpu_max_threads
hw_cpu_max_cores
hw_cpu_max_sockets
hw_cpu_realtime_mask

** Affects: nova
     Importance: Medium
         Status: Triaged

** Affects: nova/ocata
     Importance: Medium
         Status: Confirmed

** Affects: nova/pike
     Importance: Medium
         Status: Confirmed

** Affects: nova/queens
     Importance: Medium
         Status: Confirmed


** Tags: compute rebuild

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Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1763766

Title:
  nova needs to disallow topology changes on image rebuild

Status in OpenStack Compute (nova):
  Triaged
Status in OpenStack Compute (nova) ocata series:
  Confirmed
Status in OpenStack Compute (nova) pike series:
  Confirmed
Status in OpenStack Compute (nova) queens series:
  Confirmed

Bug description:
  When doing a rebuild the assumption throughout the code is that we are
  not changing the resources consumed by the guest (that is what a
  resize is for).  The complication here is that there are a number of
  image properties which might affect the instance resource consumption
  (in conjunction with a suitable flavor):

  hw_numa_nodes=X
  hw_numa_cpus.X=Y
  hw_numa_mem.X=Y
  hw_mem_page_size=X
  hw_cpu_thread_policy=X
  hw_cpu_policy=X

  Due to the assumptions made in the rest of the code, we need to add a
  check to ensure that on a rebuild the above image properties do not
  differ between the old and new images.

  
  While they might look suspicious, I think that the following image properties *should* be allowed to differ, since they only affect the topology seen by the guest:

  hw_cpu_threads
  hw_cpu_cores
  hw_cpu_sockets
  hw_cpu_max_threads
  hw_cpu_max_cores
  hw_cpu_max_sockets
  hw_cpu_realtime_mask

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