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[OpenStack Infra <1617299@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/366857
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=1af73d1fb3169c5b3cce77d94316922496bbaf9a
Submitter: Jenkins
Branch:    master

commit 1af73d1fb3169c5b3cce77d94316922496bbaf9a
Author: Tom Patzig <tom.patzig@xxxxxxx>
Date:   Wed Sep 7 11:16:49 2016 +0200

    refresh instances_path when shared storage used
    
    When doing Live migration with shared storage, it happens erratically,
    that the check for the shared storage test_file fails. Because the shared
    volume is under heavy IO (many instances on many compute nodes) the client
    does not immediately sees the new content of the folder. This delay
    could take up to 30s.
    This can be fixed if the client is forced to refresh the directories
    content, which can be achieved by 'touch' on the directory. Doing so,
    the test_file is visibile instantly, within ms.
    The patch adds a 'touch' on instances_path in check_shared_storage_test_file,
    before checking the existence of the file.
    
    Change-Id: I16be39142278517f43e6eca3441a56cbc9561113
    Closes-Bug: #1617299


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1617299

Title:
  NFS based Nova Live Migration eratically fails

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) newton series:
  Confirmed

Bug description:
  Hello,

  in our productive Openstack environment we encountered in the last weeks that Openstack Nova VM Live migrations fails.
  Currently this is only visible in our automated test environment. Every 15 minutes an automated test is started and it fails 3-4 times a day.

  On the Nova instance path we have mounted a central NetApp NFS share
  to support real Live migrations between different hypervisors.

  When we analysed the issue we found the error message and trace:
  BadRequest: <Compute-Node> is not on shared storage: Live migration can not be used without shared storage except a booted from volume VM which does not have a local disk. (HTTP 400) (Request-ID: req-8e709fd1-9d72-453b-b4b1-1f26112ea3d3)
   
  Traceback (most recent call last):
    File "/usr/lib/python2.7/site-packages/rally/task/runner.py", line 66, in _run_scenario_once
      getattr(scenario_inst, method_name)(**scenario_kwargs)
    File "/usr/lib/python2.7/site-packages/rally/plugins/openstack/scenarios/nova/servers.py", line 640, in boot_and_live_migrate_server
      block_migration, disk_over_commit)
    File "/usr/lib/python2.7/site-packages/rally/task/atomic.py", line 84, in func_atomic_actions
      f = func(self, *args, **kwargs)
    File "/usr/lib/python2.7/site-packages/rally/plugins/openstack/scenarios/nova/utils.py", line 721, in _live_migrate
      disk_over_commit=disk_over_commit)
    File "/usr/lib/python2.7/site-packages/novaclient/v2/servers.py", line 433, in live_migrate
      disk_over_commit)
    File "/usr/lib/python2.7/site-packages/novaclient/api_versions.py", line 370, in substitution
      return methods[-1].func(obj, *args, **kwargs)
    File "/usr/lib/python2.7/site-packages/novaclient/v2/servers.py", line 1524, in live_migrate
      'disk_over_commit': disk_over_commit})
    File "/usr/lib/python2.7/site-packages/novaclient/v2/servers.py", line 1691, in _action
      info=info, **kwargs)
    File "/usr/lib/python2.7/site-packages/novaclient/v2/servers.py", line 1702, in _action_return_resp_and_body
      return self.api.client.post(url, body=body)
    File "/usr/lib/python2.7/site-packages/novaclient/client.py", line 461, in post
      return self._cs_request(url, 'POST', **kwargs)
    File "/usr/lib/python2.7/site-packages/novaclient/client.py", line 436, in _cs_request
      resp, body = self._time_request(url, method, **kwargs)
    File "/usr/lib/python2.7/site-packages/novaclient/client.py", line 409, in _time_request
      resp, body = self.request(url, method, **kwargs)
    File "/usr/lib/python2.7/site-packages/novaclient/client.py", line 403, in request
      raise exceptions.from_response(resp, body, url, method)
  BadRequest: <Compute-Node> is not on shared storage: Live migration can not be used without shared storage except a booted from volume VM which does not have a local disk. (HTTP 400) (Request-ID: req-8e709fd1-9d72-453b-b4b1-1f26112ea3d3)
   
  We examined the respective hypervisors for some problems with the NFS share/mount, but everything looks really good. Also the message log file shows no issues during the test timeframe.
   
  The next step was to examine the Nova code to get a hint why Nova is bringing up such an error.
  In the Nova code we found the test procedure how Nova checks if there is a shared filesystem between source and destination hypervisor.
   
  In "nova/nova/virt/libvirt/driver.py"
   
  In function „check_can_live_migrate_destination“ a temporary file is created on the destination hypervisor:
   
  # Create file on storage, to be checked on source host
  filename = self._create_shared_storage_test_file()
   
  After that – in the same class -  in function „check_can_live_migrate_source“:
  dest_check_data.is_shared_instance_path = (
      self._check_shared_storage_test_file(
          dest_check_data.filename))
   
  will be checked if the temporary file exists. And this will sometimes fail and migration returns with this error message because the file on the source hypervisor is not yet available:
   
  elif not (dest_check_data.is_shared_block_storage or
            dest_check_data.is_shared_instance_path or
            (booted_from_volume and not has_local_disk)):
      reason = _("Live migration can not be used "
                 "without shared storage except "
                 "a booted from volume VM which "
                 "does not have a local disk.“)

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