112 lines
4.1 KiB
ReStructuredText
112 lines
4.1 KiB
ReStructuredText
==================
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pip-and-virtualenv
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==================
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This element installs pip and virtualenv in the image.
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Package install
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===============
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If the package installtype is used then these programs are installed
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from distribution packages. In this case, ``pip`` and ``virtualenv``
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will be installed *only* for the python version identified by
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``dib-python`` (i.e. the default python for the platform).
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Namespacing of the tools will be up to your distribution. Some
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distribution packages have worked out name-spacing such that only
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python2 or python3 owns common scripts like ``/usr/bin/pip`` (on most
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platforms, ``pip`` refers to python2 pip, and ``pip3`` refers to
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python3 pip, although some may choose the reverse). Other platforms
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have avoided making a decision and require explicit version suffixes.
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To install pip and virtualenv from package::
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export DIB_INSTALLTYPE_pip_and_virtualenv=package
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Source install
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==============
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.. note:: For source installs this element setups and Python 2 and
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Python 3 environments. This means it will bring in python2
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packages, so isn't appropriate if you want a python3 only
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environment.
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.. note:: Source install is considered deprecated for several reasons.
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Because it makes for a hetrogenous environment between
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distro packaged tools and upstream it means the final images
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create bespoke environments that make standarised testing
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difficult. The tricks used around holding packages to
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overwrite them cause difficulty for users of images. This
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also brings in Python 2 unconditonally, something not wanted
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on modern Python 3 only distributions.
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Source install is the default on most platforms for historical
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purposes. The current exception(s) are RHEL8 and CentOS 8.
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If the source installtype is used, ``pip`` and ``virtualenv`` are
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installed from the latest upstream releases.
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Source installs from upstream releases are not name-spaced. It is
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inconsistent across platforms if the first or last install will own
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common scripts like ``/usr/bin/pip`` and ``virtualenv``.
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To avoid inconsistency, we firstly install the packaged python 2
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**and** 3 versions of ``pip`` and ``virtualenv``. This prevents a
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later install of these distribution packages conflicting with the
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source install. We then overwrite ``pip`` and ``virtualenv`` via
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``get-pip.py`` and ``pip`` respectively.
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The system will be left in the following state:
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* ``/usr/bin/pip`` : python2 pip
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* ``/usr/bin/pip2`` : python2 pip (same as prior)
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* ``/usr/bin/pip3`` : python3 pip
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* ``/usr/bin/virtualenv`` : python2 virtualenv
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(note python3 ``virtualenv`` script is *not* installed, see below)
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Source install is supported on limited platforms. See the code, but
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this includes Ubuntu and RedHat platforms.
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Environment Variables
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=====================
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To simplify the common-case of "install a package" or "create a
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virtualenv" with the default system Python, the following variables
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are exported by this element:
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* ``DIB_PYTHON_PIP``
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* ``DIB_PYTHON_VIRTUALENV``
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This will create/install using the ``dib-python`` version for the
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platform (i.e. python2 for older distros, python3 for modern distros).
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Note that on Python 3 platforms it will use the inbuilt ``venv``
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(rather than the ``virtualenv`` package -- if you absolutely need
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features only ``virtualenv`` provides you should call it directly in
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your element; see below).
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Explicit use of the tools
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=========================
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Due to the essentially unsolvable problem of "who owns the script", it
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is recommended to *not* call ``pip`` or ``virtualenv`` directly. You
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can directly call them with the ``-m`` argument to the python
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interpreter you wish to install with.
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For example, to create a python3 environment do::
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# python3 -m virtualenv myenv
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# myenv/bin/pip install mytool
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To install a python2 tool from pip::
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# python2 -m pip install mytool
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In this way, you can always know which interpreter is being used (and
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affected by) the call.
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Ordering
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========
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Any element that uses these commands must be designated as
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05-* or higher to ensure that they are first installed.
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