diskimage-builder/elements/pip-cache/README.rst

=========
pip-cache
=========
# Use a cache for pip

Using a download cache speeds up image builds.

Including this element in an image build causes
$HOME/.cache/image-create/pip to be bind mounted as /tmp/pip inside
the image build chroot.  The $PIP_DOWNLOAD_CACHE environment variable
is then defined as /tmp/pip, which causes pip to cache all downloads
to the defined location.

Note that pip and its use of $PIP_DOWNLOAD_CACHE is not concurrency
safe.  Running multiple instances of diskimage-builder concurrently
can cause issues.  Therefore, it is advised to only have one instance
of diskimage-builder that includes the pip-cache element running at a
time.

The pip concurrency issue is being tracked upstream at
https://github.com/pypa/pip/issues/1141
Create docs site containing element READMEs We currently do not have the ability to create a docs site which outlines all the elements. Change-Id: I77ccf61e0c4b1509b3e7ce9b8f15ea5ccfd50d9b 2015-02-07 10:30:02 +00:00			`=========`
			`pip-cache`
			`=========`
Add a pip-cache element. The element bind mounts a pip cache inside the image build chroot so that pip downloads can be reused across image builds. While similar in purpose to the PyPi element that sets up a mirror, this element just allows for a reusable download cache and doesn't require anything to be setup beforehand. The pip-cache element is not concurrency safe, and that is indicated in the README for the element. An upstream bug was file as well: https://github.com/pypa/pip/issues/1141 Change-Id: Ibd1d4ea17c24923ed939357ada95b781e3179cfd 2013-08-14 18:12:15 +00:00			`# Use a cache for pip`

			`Using a download cache speeds up image builds.`

			`Including this element in an image build causes`
			`$HOME/.cache/image-create/pip to be bind mounted as /tmp/pip inside`
			`the image build chroot. The $PIP_DOWNLOAD_CACHE environment variable`
			`is then defined as /tmp/pip, which causes pip to cache all downloads`
			`to the defined location.`

			`Note that pip and its use of $PIP_DOWNLOAD_CACHE is not concurrency`
			`safe. Running multiple instances of diskimage-builder concurrently`
			`can cause issues. Therefore, it is advised to only have one instance`
			`of diskimage-builder that includes the pip-cache element running at a`
			`time.`

			`The pip concurrency issue is being tracked upstream at`
			`https://github.com/pypa/pip/issues/1141`