Comment 8 for bug 1576218

/etc/nova/nova.conf should be configured on controllers to properly manage memcached backend:
[cache]
enabled = true
backend = oslo_cache.memcache_pool
memcache_servers = {list of memcached servers to connect} # e.g. 192.168.0.6:11211, 192.168.0.7:11211, 192.168.0.7:11211