18215274d8
As described inline, deprecate the "source" install for CentOS 8. Overwriting the packaged tools has long been a pain-point in our images, and the best outcome is just not to play the game [1]. However, the landscape remains complicated. For example, RHEL/CentOS 8 introduces the separate "platform-python" binary, which seems like the right tool to install platform tools like "glean" (simple-init) with. However, platform-python doesn't have virtualenv (only the inbuilt venv). So that every element doesn't have to hard-code in workarounds for these various layouts, create two new variables DIB_PYTHON_PIP and DIB_PYTHON_VIRTUALENV to just "do the right thing". If you need is "install a pip package" or "create a virtualenv" this should work on all the platforms we support. If you know more specifically what you want (e.g. must be a python3 virtualenv) then nothing stops elements calling that directly (e.g. python3 -m virtualenv create); these are just helper wrappers for base elements that need to be broadly compatible. [1] http://lists.openstack.org/pipermail/openstack-infra/2019-September/006483.html Change-Id: Ia267a60eecfa8f4071dd477d86daebe07e9a7e38
111 lines
4.1 KiB
ReStructuredText
111 lines
4.1 KiB
ReStructuredText
==================
|
|
pip-and-virtualenv
|
|
==================
|
|
|
|
This element installs pip and virtualenv in the image.
|
|
|
|
Package install
|
|
===============
|
|
|
|
If the package installtype is used then these programs are installed
|
|
from distribution packages. In this case, ``pip`` and ``virtualenv``
|
|
will be installed *only* for the python version identified by
|
|
``dib-python`` (i.e. the default python for the platform).
|
|
|
|
Namespacing of the tools will be up to your distribution. Some
|
|
distribution packages have worked out name-spacing such that only
|
|
python2 or python3 owns common scripts like ``/usr/bin/pip`` (on most
|
|
platforms, ``pip`` refers to python2 pip, and ``pip3`` refers to
|
|
python3 pip, although some may choose the reverse). Other platforms
|
|
have avoided making a decision and require explicit version suffixes.
|
|
|
|
To install pip and virtualenv from package::
|
|
|
|
export DIB_INSTALLTYPE_pip_and_virtualenv=package
|
|
|
|
Source install
|
|
==============
|
|
|
|
.. note:: For source installs this element setups and Python 2 and
|
|
Python 3 environments. This means it will bring in python2
|
|
packages, so isn't appropriate if you want a python3 only
|
|
environment.
|
|
|
|
.. note:: Source install is considered deprecated for several reasons.
|
|
Because it makes for a hetrogenous environment between
|
|
distro packaged tools and upstream it means the final images
|
|
create bespoke environments that make standarised testing
|
|
difficult. The tricks used around holding packages to
|
|
overwrite them cause difficulty for users of images. This
|
|
also brings in Python 2 unconditonally, something not wanted
|
|
on modern Python 3 only distributions.
|
|
|
|
Source install is the default on most platforms for historical
|
|
purposes. The current exception(s) are RHEL8 and CentOS 8.
|
|
|
|
If the source installtype is used, ``pip`` and ``virtualenv`` are
|
|
installed from the latest upstream releases.
|
|
|
|
Source installs from upstream releases are not name-spaced. It is
|
|
inconsistent across platforms if the first or last install will own
|
|
common scripts like ``/usr/bin/pip`` and ``virtualenv``.
|
|
|
|
To avoid inconsistency, we firstly install the packaged python 2
|
|
**and** 3 versions of ``pip`` and ``virtualenv``. This prevents a
|
|
later install of these distribution packages conflicting with the
|
|
source install. We then overwrite ``pip`` and ``virtualenv`` via
|
|
``get-pip.py`` and ``pip`` respectively.
|
|
|
|
The system will be left in the following state:
|
|
|
|
* ``/usr/bin/pip`` : python2 pip
|
|
* ``/usr/bin/pip2`` : python2 pip (same as prior)
|
|
* ``/usr/bin/pip3`` : python3 pip
|
|
* ``/usr/bin/virtualenv`` : python2 virtualenv
|
|
|
|
(note python3 ``virtualenv`` script is *not* installed, see below)
|
|
|
|
Source install is supported on limited platforms. See the code, but
|
|
this includes Ubuntu and RedHat platforms.
|
|
|
|
Environment Variables
|
|
=====================
|
|
|
|
To simplify the common-case of "install a package" or "create a
|
|
virtualenv" with the default system Python, the following variables
|
|
are exported by this element:
|
|
|
|
* ``DIB_PYTHON_PIP``
|
|
* ``DIB_PYTHON_VIRTUALENV``
|
|
|
|
This will create/install using the ``dib-python`` version for the
|
|
platform (i.e. python2 for older distros, python3 for modern distros).
|
|
Note that on Python 3 platforms it will use the inbuilt ``venv``
|
|
(rather than the ``virtualenv`` package -- if you absolutely need
|
|
features only ``virtualenv`` provides you should call it directly in
|
|
your element; see below).
|
|
|
|
Explicit use of the tools
|
|
=========================
|
|
|
|
Due to the essentially unsolvable problem of "who owns the script", it
|
|
is recommended to *not* call ``pip`` or ``virtualenv`` directly. You
|
|
can directly call them with the ``-m`` argument to the python
|
|
interpreter you wish to install with.
|
|
|
|
For example, to create a python3 environment do::
|
|
|
|
# python3 -m virtualenv myenv
|
|
# myenv/bin/pip install mytool
|
|
|
|
To install a python2 tool from pip::
|
|
|
|
# python2 -m pip install mytool
|
|
|
|
In this way, you can always know which interpreter is being used (and
|
|
affected by) the call.
|
|
|
|
Ordering
|
|
========
|
|
Any element that uses these commands must be designated as
|
|
05-* or higher to ensure that they are first installed.
|