docs: update supported OS distros

* add CentOS Stream 8 info & reno
* mark RHEL as deprecated in docs

Change-Id: Ifa3b8c7365e4092202bf9e89b67293cf8d983e0a

doc/source/user/operating-kolla.rst

@@ -72,6 +72,15 @@ system. Ubuntu users upgrading from Ussuri should first upgrade OpenStack
 containers to Victoria, which uses the Ubuntu Focal 20.04 base container image.
 Hosts should then be upgraded to Ubuntu Focal 20.04.
 
+CentOS Stream 8
+---------------
+
+The Wallaby release adds support for CentOS Stream 8 as a host operating
+system. CentOS Stream 8 support will also be added to a Victoria stable
+release. CentOS Linux users upgrading from Victoria should first migrate hosts
+and container images from CentOS Linux to CentOS Stream before upgrading to
+Wallaby.
+
 Preparation
 -----------
 

doc/source/user/quickstart.rst

@@ -364,12 +364,12 @@ There are a few options that are required to deploy Kolla Ansible:
 
   Kolla provides choice of several Linux distributions in containers:
 
-  - CentOS
-  - Ubuntu
-  - Debian
-  - RHEL
+  - CentOS Stream (``centos``)
+  - Ubuntu (``ubuntu``)
+  - Debian (``debian``)
+  - RHEL (``rhel``, deprecated)
 
-  For newcomers, we recommend to use CentOS 8 or Ubuntu 20.04.
+  For newcomers, we recommend to use CentOS Stream 8 or Ubuntu 20.04.
 
   .. code-block:: console
 

doc/source/user/support-matrix.rst

@@ -15,9 +15,15 @@ Kolla Ansible supports the following host Operating Systems (OS):
    <https://docs.openstack.org/kolla-ansible/train/user/centos8.html>`_ for
    information on migrating to CentOS 8.
 
-* CentOS 8
-* Debian Buster (10)
-* RHEL 8
+.. note::
+
+   CentOS Linux 8 (as opposed to CentOS Stream 8) is no longer supported as a
+   host OS. The Victoria release will in future support both CentOS Linux 8 and
+   CentOS Stream 8, and provides a route for migration.
+
+* CentOS Stream 8
+* Debian Bullseye (11)
+* RHEL 8 (deprecated)
 * Ubuntu Focal (20.04)
 
 Supported container images
@@ -28,7 +34,7 @@ OS distribution. The following values are supported for ``kolla_base_distro``:
 
 * ``centos``
 * ``debian``
-* ``rhel``
+* ``rhel`` (deprecated)
 * ``ubuntu``
 
 For details of which images are supported on which distributions, see the

releasenotes/notes/centos-stream-686441cc4c0e47d7.yaml

@@ -0,0 +1,13 @@
+---
+features:
+  - |
+    Adds support for CentOS Stream 8 as a host Operating System and base
+    container image. This is the only distribution of CentOS supported from
+    the Wallaby release. The Victoria release will support both CentOS Linux 8
+    and CentOS Stream 8 hosts and images, and provides a route for migration.
+upgrade:
+  - |
+    CentOS Linux 8 is no longer supported as a host Operating System or base
+    container image. CentOS users should migrate to CentOS Stream 8. The
+    Victoria release will support both CentOS Linux 8 and CentOS Stream 8
+    hosts and images, and provides a route for migration.