Ask HN: Tips to Reduce Docker Image Sizes
What are some of the most common and advanced tips to reduce docker image sizes? For Rails app, for python app. For docker images in general?
A quick-and-dirty way that doesn't require rewriting is just to use the experimental --squash flag[1] (i.e. add: --experimental --squash) when running docker (you can also turn on --experimental permanently by putting { "experimental": true } into docker's /etc/docker/daemon.json file. And, on a Mac, you can open the Docker app and there's a checkbox to turn on experimental features and then you can just use --squash in the terminal).
Anecdotally, I had a 4.67GB docker file that --squash reduced to a little over 1GB. However, a rewrite of the docker file to do a multi-stage build took that 4.67GB file down to just under 0.5GB.
P.S. Pro-tip: if you want to speed up your docker builds, if you're using 18.06 or higher, you can use use buildkit [2]. Again, anecdotally, on a 6-core Macbook from 2019 I think I got a 30% speedup or so -- your mileage may vary (a colleague with an 8-core machine I think got a 50% speedup -- it's been a while, so these percentages may be a bit off, but you get the idea).
It was also an experimental feature early on, so you needed to have experimental features turned on (as described above with --squash). With later versions you don't need to do that -- check your version's documentation.
Anyway, you can either set an environment variable to use it i.e. export DOCKER_BUILDKIT=1 or you can set this permanently by adding: {"features":{"buildkit": true}} to /etc/docker/daemon.json
[0] https://blog.logrocket.com/reduce-docker-image-sizes-using-m...
[1] https://docs.docker.com/develop/develop-images/multistage-bu...
[2] https://www.giantswarm.io/blog/container-image-building-with...