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[OpenStack Infra <1807044@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/623284
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=d779b33d72d6ef41651ce7b93fe982f121bae2d7
Submitter: Zuul
Branch:    master

commit d779b33d72d6ef41651ce7b93fe982f121bae2d7
Author: Dan Smith <dansmith@xxxxxxxxxx>
Date:   Thu Dec 6 08:07:37 2018 -0800

    Make compute rpcapi version calculation check all cells
    
    For top-level services, the compute rpcapi module needs to check for the
    minimum version of nova-compute in all cells in order to function
    properly during an upgrade. This moves that module to use the all-cells
    variant of this routine in the case where [api_database]/connection is
    set.
    
    Change-Id: Icddbe4760eaff30e4e13c1e8d3d5d3f489dac3c4
    Closes-Bug: #1807044


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

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https://bugs.launchpad.net/bugs/1807044

Title:
  nova-api startup does not scan cells looking for minimum nova-compute
  service version

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) pike series:
  Confirmed
Status in OpenStack Compute (nova) queens series:
  Confirmed
Status in OpenStack Compute (nova) rocky series:
  Confirmed

Bug description:
  This CI job failed devstack setup because nova-api took longer than 60
  seconds to start (it took 64 seconds):

  http://logs.openstack.org/01/619701/5/gate/tempest-
  slow/2bb461b/controller/logs/screen-n-api.txt.gz

  Looking at what could be taking time in there, it was noticed that
  this is logged a lot:

  Dec 05 20:14:00.919520 ubuntu-xenial-ovh-bhs1-0000959981
  devstack@n-api.service[23459]: DEBUG nova.compute.rpcapi [None req-
  dfdfad07-2ff4-43ed-9f67-2acd59687e0c None None] Not caching compute
  RPC version_cap, because min service_version is 0. Please ensure a
  nova-compute service has been started. Defaulting to current version.
  {{(pid=23462) _determine_version_cap
  /opt/stack/nova/nova/compute/rpcapi.py:397}}

  That's coming from here:

  https://github.com/openstack/nova/blob/aed3e240138ad84352688611246363339414c98f/nova/compute/rpcapi.py#L396

  Which is when the compute rpcapi client is initialized, which happens
  when nova.compute.api.API is initialized:

  https://github.com/openstack/nova/blob/aed3e240138ad84352688611246363339414c98f/nova/compute/api.py#L266

  Which happens for most of the API extensions, e.g.:

  https://github.com/openstack/nova/blob/aed3e240138ad84352688611246363339414c98f/nova/api/openstack/compute/servers.py#L78

  So that init and DB query happens num_workers * num_extensions times
  (we have 2 workers in this case and it looks like there are at least
  29 instantiations of the compute API code in the extensions).

  The bigger problem is that in this case, nova-api is configured to hit
  cell0 for the [database]/connection:

  http://logs.openstack.org/01/619701/5/gate/tempest-
  slow/2bb461b/controller/logs/etc/nova/nova_conf.txt.gz

  [database]
  connection = mysql+pymysql://root:secretdatabase@127.0.0.1/nova_cell0?charset=utf8

  And there will not be nova-compute services in the cell0 database (if
  configured properly).

  So this query is always going to return 0, at least for devstack:

  https://github.com/openstack/nova/blob/aed3e240138ad84352688611246363339414c98f/nova/compute/rpcapi.py#L387

  We should really be scanning the cells to get the minimum nova-compute
  version using this:

  https://github.com/openstack/nova/blob/aed3e240138ad84352688611246363339414c98f/nova/objects/service.py#L481

  But even on first startup of nova-api before any computes are started
  and registered with a cell, that initial query will return 0 which
  means we won't cache the result and continue to do that query and log
  that message for extensions * workers.

  So there are really kind of two issues here:

  1. We're not iterating cells properly for that version check. This is
  the more important issue.

  2. We're needlessly doing this query on initial startup which slows
  down the startup (and contributes to timeouts the devstack jobs on
  slow nodes) and lots of excessive logging.

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