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Reviewed:  https://review.openstack.org/610034
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=00d08a3288f61268f8a823991fadf0d83c36c04d
Submitter: Zuul
Branch:    master

commit 00d08a3288f61268f8a823991fadf0d83c36c04d
Author: Sean Mooney <work@xxxxxxxxxxxxxxx>
Date:   Fri Oct 12 14:26:14 2018 +0100

    Harden placement init under wsgi
    
    - This change tries to address an edge case discovered
      when running placement under mod_wsgi where
      if the placement wsgi application is re-initialize the db_api
      configure method attempts to reconfigure a started transaction
      factory.
    
    - This since oslo.db transaction factories do not support
      reconfiguration at runtime this result in an exception being
      raised preventing reloading of the Placement API without
      restarting apache to force mod_wsgi to recreate the
      python interpreter.
    
    - This change introduces a run once decorator to allow annotating
      functions that should only be executed once for the lifetime fo
      an interpreter.
    
    - This change applies the run_once decorator to the db_api configure
      method, to suppress the attempt to reconfigure the current
      TransactionFactory on application reload.
    
    Co-Authored-By: Balazs Gibizer <balazs.gibizer@xxxxxxxxxxxx>
    Closes-Bug: #1799246
    Related-Bug: #1784155
    Change-Id: I704196711d30c1124e713ac31111a8ea6fa2f1ba


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

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https://bugs.launchpad.net/bugs/1799246

Title:
  module level init of db transation contexts cause failure under
  mod_wsgi on module reload

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  Description
  ===========
  This is related to a downstream bug first reported here:https://bugzilla.redhat.com/show_bug.cgi?id=1630069 where in it was discovers that due to how
  triplo currently deploys the placemetn api under mod_wsgi

  when deployed under mod_wsgi if the wsgi application exits with an error it is reloaded
  back into the same python interperter instance. As a result of this behavior module level 
  variable have a longer lifetime then the lifetime of the application. when run under uwsgi
  when the application is reloaded it is reloaded in a new python interperter meaning 
  the lifetime of the module level variables is scoped to the life time of the application.

  As a result of the life time semantics of mod_wsgi the placment api and nova-api
  must assume that the wsgi applications init can be invoked multiple times on failure.
  The current use of the sqlalcamey enginefacade transaction_context is not reentrant
  resulting in a type error being raised on subsequet calls to configure when the wsgi
  application is reloaded. 

  
  Expected result
  ===============
  it should be possible to reload the nova and placement api wsgi application
  under mod_wsgi on failure 

  Actual result
  =============

  46087 [Wed Oct 10 15:10:49.433284 2018] [:error] [pid 14] [remote 172.25.0.10:208] mod_wsgi (pid=14): Target WSGI script '/var/www/cgi-bin/nova/nova-placement-api' cannot be loaded as Python module.
  46088 [Wed Oct 10 15:10:49.433305 2018] [:error] [pid 14] [remote 172.25.0.10:208] mod_wsgi (pid=14): Exception occurred processing WSGI script '/var/www/cgi-bin/nova/nova-placement-api'.
  46089 [Wed Oct 10 15:10:49.433320 2018] [:error] [pid 14] [remote 172.25.0.10:208] Traceback (most recent call last):
  46090 [Wed Oct 10 15:10:49.433333 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/var/www/cgi-bin/nova/nova-placement-api", line 54, in <module>
  46091 [Wed Oct 10 15:10:49.433354 2018] [:error] [pid 14] [remote 172.25.0.10:208]     application = init_application()
  46092 [Wed Oct 10 15:10:49.433361 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/nova/api/openstack/placement/wsgi.py", line 108, in init_application
  46093 [Wed Oct 10 15:10:49.433386 2018] [:error] [pid 14] [remote 172.25.0.10:208]     db_api.configure(conf.CONF)
  46094 [Wed Oct 10 15:10:49.433392 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/nova/api/openstack/placement/db_api.py", line 35, in configure
  46095 [Wed Oct 10 15:10:49.433403 2018] [:error] [pid 14] [remote 172.25.0.10:208]     **_get_db_conf(conf.placement_database))
  46096 [Wed Oct 10 15:10:49.433408 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 788, in configure
  46097 [Wed Oct 10 15:10:49.433420 2018] [:error] [pid 14] [remote 172.25.0.10:208]     self._factory.configure(**kw)
  46098 [Wed Oct 10 15:10:49.433425 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/debtcollector/renames.py", line 43, in decorator
  46099 [Wed Oct 10 15:10:49.433435 2018] [:error] [pid 14] [remote 172.25.0.10:208]     return wrapped(*args, **kwargs)
  46100 [Wed Oct 10 15:10:49.433440 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 312, in configure
  46101 [Wed Oct 10 15:10:49.433449 2018] [:error] [pid 14] [remote 172.25.0.10:208]     self._configure(False, kw)
  46102 [Wed Oct 10 15:10:49.433453 2018] [:error] [pid 14] [remote 172.25.0.10:208]   File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 317, in _configure
  46103 [Wed Oct 10 15:10:49.433462 2018] [:error] [pid 14] [remote 172.25.0.10:208]     raise TypeError("this TransactionFactory is already started")
  46104 [Wed Oct 10 15:10:49.433473 2018] [:error] [pid 14] [remote 172.25.0.10:208] TypeError: this TransactionFactory is already started

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