docker: fast CI rebuilds with --cache-from (intermediate) anthony explains #448

today I show how to speed up docker builds by using `--cache-from` (and why it's necessary at all!)

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[nilesh-gule]

Thanks for the wonderful explanation Anthony. Wish this feature worked with the multistage Dockerfile builds as well.

[panteliskaramolegkos]

What are the differences between the --cache-from flag in docker build and the RUN --mount type=cache in the Dockerfile itself? Are BOTH needed to leverage cache?

[ndepal]

Do I need to have pulled the image before or will it be pulled automatically if I don't have it yet? Does this also work with buildx? I think that normally doesn't look at local images as it has its own cache?