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CentOS 8 nodes available now


Hello,

I'm happy to say that CentOS 8 images are now live in OpenDev infra.
Using a node label of "centos-8" will get you started.

---

The python environment setup on these images is different to our other
images.  Firstly, some background: currently during image build we go
to some effort to:

a) install the latest pip/virtualenv/setuptools
b) ensure standard behaviour:
    /usr/bin/python     -> python2
    /usr/bin/pip        -> python2 install
    /usr/bin/pip3       -> python3 install
    /usr/bin/virtualenv -> creates python2 environment by default;
                           python3 virtualenv package in sync

This means a number of things; hosts always have python2, and because
we overwrite the system pip/virtualenv/setuptools we put these
packages on "hold" (depending on the package manager) so jobs don't
re-install them and create (even more of) a mess.

This made sense in the past, when we had versions of pip/setuptools in
distributions that couldn't understand syntax in requirements files
(and other bugs) and didn't have the current fantastic job inheritance
and modularity that Zuul (v3) provides.  However, it also introduces a
range of problems for various users, and has a high maintenance
overhead.

Thus these new images are, by default, python3 only, and have upstream
pip and virtualenv packages installed.  You will have a default
situation:

 /usr/bin/python -> not provided
 /usr/bin/pip    -> not provided, use /usr/bin/pip3 or "python3 -m pip"
 /usr/bin/virtualenv -> create python3 environment;
                        provided by upstream python3-virtualenv package
 /usr/bin/pyvenv -> not provided (is provided by Ubuntu python3-venv),
                    use /usr/bin/pyvenv-3 or "python3 -m venv".

Ergo, the "standard behaviour" is not so standard any more.

I would suggest if you wish to write somewhat portable jobs/roles
etc., you do the following:

 * in general don't rely on "unversioned" calls of tools at all
   (python/pip/virtualenv) -- they can all mean different things on
   different platforms.
 * scripts should always be #!/usr/bin/python3
 * use "python3 -m venv" for virtual environments (if you really need
   "virtualenv" because of one of the features it provides, use "-m
   virtualenv")
 * use "python3 -m pip" to install global pip packages; but try not
   too -- mixing packages and pip installs never works that well.
 * if you need python2 for some reason, use a bindep file+role
   to install it (don't assume it is there)

---

For any Zuul admins, note that to use python3-only images similar to
what we make, you'll need to set "python-path" to python3 in nodepool
so that Ansible calls the correct remote binary.  Keep an eye on [1]
which will automate this for Ansible >=2.8 after things are merged and
released.

---

Most of the job setup has been tested (network configs, setting
mirrors, adding swap etc.) but there's always a chance of issues with
a new platform.  Please bring up any issues in #openstack-infra and
we'll be sure to get them fixed.

---

If you're interested in the images, they are exported at

 https://nb01.openstack.org/images/

although they are rather large, because we pre-cache a lot.  If you'd
like to build your own, [2] might help with:

 DISTRO=centos-minimal
 DIB_RELEASE=8

---

Thanks,

-i

[1] https://review.opendev.org/#/c/682797/
[2] https://opendev.org/openstack/project-config/src/branch/master/tools/build-image.sh