Comment 9 for bug 1829062

Note that we are assuming from the error message:

  2019-05-14 00:44:03.636792 error: cannot switch to a different thread

that your wsgi app is configured with threads > 1.

Another workaround is to configure the wsgi app with threads=1, which will have each nova-api process use one thread. This workaround is useful if you do not want to serialize multi-cell queries in a large multiple cell deployment by setting OS_NOVA_DISABLE_EVENTLET_PATCHING=yes.