Open Stack

Hello,

All our current images use dib's "pip-and-virtualenv" element to
ensure the latest pip/setuptools/virtualenv are installed, and
/usr/bin/<pip|virtualenv> installs Python 2 packages and
/usr/bin/<pip3|virtualenv3> install Python 3 packages.

The upshot of this is that all our base images have Python 2 and 3
installed (even "python 3 first" distros like Bionic).

We have to make a decision if we want to continue this with CentOS 8;
to be specific the change [1].

Installing pip and virtualenv from upstream sources has a long history
full of bugs and workarounds nobody wants to think about (if you do
want to think about it, you can start at [2]).

A major problem has been that we have to put these packages on "hold",
to avoid the situation where the packaged versions are re-installed
over the upstream versions, creating a really big mess of mixed up
versions.

I'm thinking that CentOS 8 is a good place to stop this.  We just
won't support, in dib, installing pip/virtualenv from source for
CentOS 8.  We hope for the best that the packaged versions of tools
are always working, but *if* we do require fixes to the system
packages, we will implement that inside jobs directly, rather than on
the base images.

I think the 2019 world this is increasingly less likley, as we have
less reliance on older practices like mixing system-wide installs
(umm, yes devstack ... but we have a lot of work getting centos8
stable there anyway) and the Zuul v3 world makes it much easier to
deploy isloated fixes as roles should we need.

If we take this path, the images will be Python 3 only -- we recently
turned Ansible's "ansible_python_interpreter" to Python 3 for Fedora
30 and after a little debugging I think that is ready to go.  Of
course jobs can install the Python 2 environment should they desire.

Any comments here, or in the review [1] welcome.

Thanks,

-i

[1] https://review.opendev.org/684462
[2] https://opendev.org/openstack/diskimage-builder/src/branch/master/diskimage_builder/elements/pip-and-virtualenv/install.d/pip-and-virtualenv-source-install/04-install-pip#L73