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[zhu zhu <zhuzhubj@xxxxxxxxxx>]

Public bug reported:

As for the nova scheduler for scheduler multiple attempts,  If with
certain host deployment attempt failed raise with detail exceptions,
nova scheduler will choose other host to retry.

But after all attempts are tried. it will raise a Generic NoValidHost
exception without a proper message.  It will make nova show  <instance>
will not display useful information straightforward to end users.

So it's suggested to wrap the NoValidHost exception message  with last
attempt failure exception detail trace.

For example,
When using nova vmware driver to spawn a VM with the disk larger than the datastore upper limit, it will raise an exception 
for DatastoreNotFound exception with detail, but after scheduler retries, it will got lost from nova show. So it would be friendly to have operators to view such error directly from the nova show instead for digging into the scheduler log. 

filter_scheduler.py

schedule_run_instance

        for num, instance_uuid in enumerate(instance_uuids):
            request_spec['instance_properties']['launch_index'] = num

            try:
                try:
                    weighed_host = weighed_hosts.pop(0)
                    LOG.info(_("Choosing host %(weighed_host)s "
                                "for instance %(instance_uuid)s"),
                              {'weighed_host': weighed_host,
                               'instance_uuid': instance_uuid})
                except IndexError:
                    raise exception.NoValidHost(reason="")

** Affects: nova
     Importance: Undecided
         Status: New


** Tags: scheduler

** Summary changed:

- Nova show will not display NoValidHost with detail exception traces
+ Nova show will not display NoValidHost with right exception traces

** Tags added: scheduler

-- 
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Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1369818

Title:
  Nova show will not display NoValidHost with right exception traces

Status in OpenStack Compute (Nova):
  New

Bug description:
  As for the nova scheduler for scheduler multiple attempts,  If with
  certain host deployment attempt failed raise with detail exceptions,
  nova scheduler will choose other host to retry.

  But after all attempts are tried. it will raise a Generic NoValidHost
  exception without a proper message.  It will make nova show
  <instance> will not display useful information straightforward to end
  users.

  So it's suggested to wrap the NoValidHost exception message  with last
  attempt failure exception detail trace.

  For example,
  When using nova vmware driver to spawn a VM with the disk larger than the datastore upper limit, it will raise an exception 
  for DatastoreNotFound exception with detail, but after scheduler retries, it will got lost from nova show. So it would be friendly to have operators to view such error directly from the nova show instead for digging into the scheduler log. 

  filter_scheduler.py

  schedule_run_instance

          for num, instance_uuid in enumerate(instance_uuids):
              request_spec['instance_properties']['launch_index'] = num

              try:
                  try:
                      weighed_host = weighed_hosts.pop(0)
                      LOG.info(_("Choosing host %(weighed_host)s "
                                  "for instance %(instance_uuid)s"),
                                {'weighed_host': weighed_host,
                                 'instance_uuid': instance_uuid})
                  except IndexError:
                      raise exception.NoValidHost(reason="")

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