[kolla][openstack-ansible][tripleo] CentOS 8 host migration
aschultz at redhat.com
Mon Nov 25 18:03:28 UTC 2019
On Mon, Nov 25, 2019 at 10:54 AM Mark Goddard <mark at stackhpc.com> wrote:
> During the recent kolla PTG discussions , we covered CentOS 8 in
> some detail. For kolla there are several aspects to CentOS 8 support:
> * kolla-build execution host
> * container images
> * kolla-ansible execution host
> * kolla-ansible remote hosts
> In this context I am discussing the last of these - kolla-ansible
> remote hosts, i.e. the OS on the controllers and computes etc. Given
> that this could be quite a thorny problem, I'd like to propose that we
> collaborate between deployment projects.
> It is my understanding that upgrades from CentOS 7 to 8 will not be
> supported, and a reinstall is required. We set out some goals for the
> * Migrate hosts from CentOS 7 to CentOS 8
> * Upgrade from Train CentOS 7 containers to Ussuri CentOS 8 containers
> * Note: this means Ussuri containers (CentOS 8) don't land on CentOS 7
> * Decouple the CentOS 7 to 8 and OpenStack upgrades, to avoid operator pain
> * Avoid excessive downtime
> There is a Red Hat policy  that suggests that if you mix host and
> container OS versions, it is safer for the host to be ahead of the
> container. This makes sense if you think about userland accessing
> kernel features.
> This leads us to the following migration path:
> * Start with Train release, CentOS 7 containers
> * Redeploy (rolling) hosts with CentOS 8
> * Provision
> * Configure host OS
> * Redeploy Train containers with CentOS 7
* Upgrade to Ussuri release, CentOS 8 containers
> The logic we used to come up with this procedure is as follows:
> * Host must be upgraded to CentOS 7 before containers (going on policy)
> * Train containers don't support CentOS 8 base due to RDO
I believe the plan is to have a Train version on CentOS8 after all the
things get bootstrapped. Unfortunately the current target is trying to get
master on centos8 with the time frame currently TBD. I'm personally hoping
> * Ussuri containers don't support CentOS 7 base due to RDO
> * Want to separate CentOS 7 -> 8 migration from OpenStack upgrade
> This leads us to the conclusion that at least one release of
> kolla-ansible must bridge these worlds, since we will be deploying
> Train containers on CentOS 8. We could do either of:
> 1. Train k-a supports CentOS 8 hosts
> 2. Ussuri k-a supports deploying Train containers
> While 1. may require us to backport more than we would like,
> supporting deployment of multiple OpenStack releases could be
> challenging, so we expect to go with 1 here.
> There are some risks involved, including:
> * some Train services may not work on CentOS 8
> * ceph?
> * OVS & neutron agents?
> * libvirt?
> * Ansible minimum version 2.8 for CentOS 8 (ref?)
These should be fine as we're testing these with actual rhel8 over in
TripleO (at least builds/running) for Train+. You'll run into other issues
with pacemaker if you currently use that and try to mix versions.
Bigger risk: lack of docker packaging in the upstream which also means no
docker-distribution for local repositories.
> Hopefully we can save ourselves some effort and solve this together.
>  https://etherpad.openstack.org/p/kolla-ussuri-ptg
>  https://access.redhat.com/support/policy/rhel-container-compatibility
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