Control Disk use of /var/lib/docker/overlay2

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:

  • List item

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?