Deployment of OpenStack with train-centos8 images on host with Centos 7 is failing

[Oliver Horecny]

Environment
===========
- SETUP: all in one setup
- OS: CentOS Linux release 7.4.1708 (Core)
- KERNEL: 3.10.0-693.el7.x86_64
- DOCKER VERSION: 18.06.1-ce
- DOCKER IMAGES: binary

Description
===========
It seems that kolla-ansible doesn't support deployment of OpenStack Train with centos8 images on centos7 host (same issue will be with RedHat too). In kolla-ansible there are few places where is needed to decide which mechanism will be used inside container based on OS version (e.g. used python version). Deployment is failing, because there is used ansible variable "ansible_distribution_major_version" which is version of host OS. For this purpose is needed to use OS version inside container.
During my testing of all-in-one deployment I needed to change this files for successful deployment:

- in kolla-ansible/ansible/roles/haproxy/templates/haproxy_run.sh.j2 I needed to change command to use haproxy (not that haproxy-systemd-wrapper)

- in kolla-ansible/ansible/group_vars/all.yml I needed to change python version to 3.6 in case of centos7 too

For my testing I just hardcoded that command and python version, which should be taken based on OS. But I am pretty sure that it will need adaptations on more places. I think this should be taken somehow automatically and this kind of deployment should be successful.

Steps to reproduce
==================
Deployment of OpenStack Train based on Centos 8 on host with Centos 7.

Expected result
===============
Successful deployment of OpenStack Train.

[Mark Goddard (mgoddard)]

This configuration is not supported. Please use the same major version for the host and containers.

[Radosław Piliszek (yoctozepto)]

Nonetheless, the mentioned places are indeed using the wrong "side".

[Mark Goddard (mgoddard)]

I don't follow you Radek.

[Radosław Piliszek (yoctozepto)]

Ok, let me rephrase that. It is indeed a fact that Kolla Ansible assumes here, for the container images, the same version as running on the host.

[Oliver Horecny (horecoli)]

So no action regarding this from community side, right? I thought that docker images/containers are independent on host and as I mentioned in description with some changes I was able to deploy OpenStack. So we do not need a lot for support this case.

[Mark Goddard (mgoddard)]

If you have simple fixes to make this work, you can propose them and we may accept them. However, we still recommend to use the same major CentOS version for the host and container.

[Michal Nasiadka (mnasiadka)]

Train is EOL