Reduce Docker image size by only copying pip installed dependencies

[adamantike]

Currently, the multi-stage Docker build makes the release stage inherit from dependencies, which will include any files created by the pip install process in the final image.

By using pip install --user to make dependencies be installed in ~/.local, we can only copy those files into the final image, reducing the image size:

cloudflare-ddns-fix-applied     latest            68427bd7c88d   3 minutes ago   54.6MB
cloudflare-ddns-master          latest            2675320b651d   8 minutes ago   65.9MB

A good resource to go deeper on how this approach works can be found at https://pythonspeed.com/articles/multi-stage-docker-python/, solution 1.

[timothymiller]

I'll re-open this if it causes issues

[bobdoah]

This breaks running as non-root user in Kubernetes. The image fails with:

Traceback (most recent call last):                                                                                                                                                                       
  File "/cloudflare-ddns.py", line 17, in <module>                                                                                                                                                         
    import requests                                                                                                                                                                                   
ModuleNotFoundError: No module named 'requests'                                                                                                                                                       

because the directory being copied to (/root/.local) is not the non-root users home directory, nor is it accessible. The runAsNonRoot is generally considered best practice. The runAsUser configuration is a fallback when the image does not specify a USER.

[douglasparker]

Can we revert this until #162 is resolved? This has broken running as non-root for over 2 months; which is kind of a big deal.

[adamantike]

@bobdoah, thanks for working on the fix! I didn't test these changes with non-root users, but should have. Having #162 merged would be great, and #150 would also be a good addition, for people to be able to use previous versions when latest is broken.