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Merge "Add an issue releasenote for placement eventlet stall" into stable/stein

changes/19/679519/1
Zuul 3 weeks ago
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      releasenotes/notes/placement-eventlet-stall-ffcca23a6a364c78.yaml

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+---
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+issues:
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+  - |
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+    In Stein the Placement service is available either as part of Nova, or
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+    independently packaged from its own project. This is to allow easier
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+    migration from one to another. See the `upgrade notes`_ for more
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+    information.
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+
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+    When using the Placement packaged from Nova, some deployment strategies can
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+    lead to the service stalling with error messages similar to::
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+
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+        Traceback (most recent call last):
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+          File "/usr/lib/python2.7/site-packages/eventlet/hubs/hub.py", line 460, in fire_timers
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+            timer()
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+          File "/usr/lib/python2.7/site-packages/eventlet/hubs/timer.py", line 59, in __call__
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+            cb(*args, **kw)
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+          File "/usr/lib/python2.7/site-packages/eventlet/semaphore.py", line 147, in _do_acquire
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+            waiter.switch()
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+        error: cannot switch to a different thread
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+
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+    The reasons this is happening are discussed in bug 1829062_. There are
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+    three workarounds available:
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+
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+    * In the environment of the web server running the placement service, set
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+      ``OS_NOVA_DISABLE_EVENTLET_PATCHING=yes`` so that eventlet does not
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+      conflict with thread handling in the web server.
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+
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+    * Turn off threading in the web server. For example, if using ``mod_wsgi``
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+      or ``uwsgi``, set ``threads=1`` in their respective configurations.
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+
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+    * Switch to using the extracted placement. It does not suffer from eventlet.
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+
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+    .. _upgrade notes: https://docs.openstack.org/placement/latest/upgrade/to-stein.html
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+    .. _1829062: https://bugs.launchpad.net/nova/+bug/1829062

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