I've upgraded systemd across my cluster to 229-4ubuntu6, removed all my custom tweaks to systemd settings, reloaded the daemon and both rabbitmq and mysql appear to be working fine on my openstack cluster. I'll be throwing a bit more load at it, but usually by this point mysql has fallen over, so I'd say this is a success.
I've upgraded systemd across my cluster to 229-4ubuntu6, removed all my custom tweaks to systemd settings, reloaded the daemon and both rabbitmq and mysql appear to be working fine on my openstack cluster. I'll be throwing a bit more load at it, but usually by this point mysql has fallen over, so I'd say this is a success.