With the release of 4.2.0 of keystonemiddleware using the
in-process token cache is no longer recommended. It is recommended
that a memcache backend to store tokens is used instead,
This installs and configures memcache and configures ceilometer agent
to use memcache for token caching.
http://docs.openstack.org/releasenotes/keystonemiddleware/mitaka.html#id2
Change-Id: If7dd4c5472a7842f06d0fd44c1b2012c9c9d1075