[Bug 1766543] Re: instance deletion takes a while and blocks nova-compute

[James Page]

Raising a task for the kernel for an opinion on how to triage this
problem further; Marking the nova task as Medium but leaving as New for
now until we figure out what's going on - this is not a show stopped but
is a pain.

** Also affects: linux (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: nova (Ubuntu)
   Importance: Undecided => Medium

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Title:
  instance deletion takes a while and blocks nova-compute

Status in linux package in Ubuntu:
  Incomplete
Status in nova package in Ubuntu:
  New

Bug description:
  Hi,

  I have a cloud running xenial/mitaka (with 18.02 charms).

  Sometimes, an instance will take minutes to delete. I tracked down the
  time taken to be file deletion :

  Apr 23 07:23:00 hostname nova-compute[54255]: 2018-04-23 07:23:00.920
  54255 INFO nova.virt.libvirt.driver [req-
  35ccfe64-9280-4de6-ae88-045ca91bf90f bc0ab055427645aca4ed09266e85b1db
  1cb457a8302543fea067e5f14b5241e7 - - -] [instance: 97731f51-63be-4056
  -869f-084b38580b9a] Deleting instance files
  /srv/nova/instances/97731f51-63be-4056-869f-084b38580b9a_del

  Apr 23 07:27:33 hostname nova-compute[54255]: 2018-04-23 07:27:33.767
  54255 INFO nova.virt.libvirt.driver [req-
  35ccfe64-9280-4de6-ae88-045ca91bf90f bc0ab055427645aca4ed09266e85b1db
  1cb457a8302543fea067e5f14b5241e7 - - -] [instance: 97731f51-63be-4056
  -869f-084b38580b9a] Deletion of /srv/nova/instances/97731f51-63be-4056
  -869f-084b38580b9a_del complete

  
  As you can see, 4 minutes and 33 seconds have elapsed between the 2 lines. nova-compute logs absolutely _nothing_ during this time. Periodic tasks are not run, etc... Generally, a deletion takes a few seconds top.

  The logs above are generally immediately followed by :

  Apr 23 07:27:33 hostname nova-compute[54255]: 2018-04-23 07:27:33.771
  54255 DEBUG oslo.messaging._drivers.impl_rabbit [req-
  35ccfe64-9280-4de6-ae88-045ca91bf90f bc0ab055427645aca4ed09266e85b1db
  1cb457a8302543fea067e5f14b5241e7 - - -] Received recoverable error
  from kombu: on_error /usr/lib/python2.7/dist-
  packages/oslo_messaging/_drivers/impl_rabbit.py:683

  (which is error: [Errno 104] Connection reset by peer)

  because nova-compute doesn't even maintain the rabbitmq connection (on
  the rabbitmq server I can see errors about "Missed heartbeats from
  client, timeout: 60s").

  So nova-compute appears to be "frozen" during several minutes. This
  can cause problems because events can be missed, etc...

  We have telegraf on this host, and there's little to no CPU, disk,
  network or memory activity at that time. Nothing relevant in kern.log
  either. And this is happening on 3 different architectures, so this is
  all very puzzling.

  Is nova-compute supposed to be totally stuck while deleting instance
  files ? Have you ever seen something similar ?

  I'm going to try to repro on queens.

  Thanks

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