no-cache-dir patch bomb

Monty Taylor mordred at
Thu Jun 18 11:57:35 UTC 2020

Hi all!

We’ve apparently just gotten a bazillion patches uploaded that do a global search and replace to add —no-cache-dir to all of the pip commands it can find. I have a couple of issues with this and think people should be very careful about landing them

a) —no-cache-dir is NOT universally a good idea, and in many cases for interactive install using it will be a worse user experience. The linked post is specifically about reducing docker image size.

b) Importantly, it’s updating all of the end-user installation docs. That is highly inappropriate and makes our docs much more user unfriendly, especially given (a)

c) In some install scripts we’re going to run them potentially in devstack. While constraints SHOULD prevent a large amount of reinstalling of different versions of things over and over, we all know reality is messier. I think we want to think carefully about removing cache dir usage in devstack as it could actually lead to an increase in install time, and optimizing for docker image size is not a thing we’re attempting to do in functional tests.

Regarding the docker image size optimization, for those who are building docker images, I would highly recommend either installing from bistro packages or using builder-image pattern instead. We have one implemented in opendevorg/python-builder and opendevorg/python-base - but the pattern can be implemented elsewhere. The main idea/benefit is to use a builder image to install dev tools and -dev packages with headers and things needed to build wheels, build wheels for all of the dependencies - then in a second build stage copy the wheels from the builder image and install them. We’re using a “compile” tag in binder to indicate what packages are needed for compile-time tasks. The savings from this can be substantial - obviously at the cost of greater complexity.

In any case, I HIGHLY recommend not landing any of these patches as submitted.


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