[Rdo-list] OpenStack upgrade Icehouse Centos 6 best practice

Hello, We currently plan to upgrade our Openstack setup from Icehouse to Juno or even Kilo. This also includes a version upgrade on the host based OS from Centos 6.6 to 7.x I have some questions regarding the upgrade an hope to learn from your experience. First question is, is there a Openstack version compatibility guaranteed within the different releases? The idea behind it to upgrade the different services (compute nodes / management nodes) in separate phases. Second, is the live-migration with block-migrate feature compatible between versions. One upgrade solution we currently playing with is to move existing VMs with live-migration & block-migrate (no shared storage) to fresh installed Centos 7 Kilo compute nodes. Any best practice tips highly appreciated! Cheers, Chris