What is the best way to maintain disk usage by Docker? Namely, how do you prevent var/lib/docker/overlay2 from endlessly filling up? I’ve seen plenty of insights on this, but no definitive answer. I am using Docker 20.10.2 on Ubuntu 20.04.1 running 2 containers: a web server (Nginx + Gunicorn + Django) and a postgreSQL Database. NOTE: I am also using Docker with Dokku here.
I have:
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used docker system prune and pruned images and containers separately as well (with each combination of flags). These reclaimed minimal space.
- tried to manually delete some of the directories in overlay2 (broke Docker installation)
- uninstalled, reinstalled Docker and rebuilt my containers with new images, and overlay2 started to balloon again immediately.
When I see what the largest files are inside one of these /<hash/ directories: 
It looks like the directory contains images, yet the docker image commands weren’t helping me reclaim anything.
How can I safely reclaim overlay2 right now? and Is there any way to prevent this issue from arising in the future?