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0702ce9843
diskimage-builder/elements/pip-cache
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James Slagle 0702ce9843 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
2013-08-26 15:17:41 -04:00
..
environment.d Add a pip-cache element. 2013-08-26 15:17:41 -04:00
root.d Add a pip-cache element. 2013-08-26 15:17:41 -04:00
README.md Add a pip-cache element. 2013-08-26 15:17:41 -04:00

README.md

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