I had some trouble with my Cloudron. Found out that the disk was getting full, and managed to fix that with the instructions at https://cloudron.io/documentation/server/#recovery-after-disk-full
However, I investigated a bit what was taking up so much space. It turns out that by far the biggest culprit is /var/lib/docker/overlay2 which has about 450 subfolders and uses 16 GB of my 45 GB drive. (determined with "du -x", i.e. skipping anything that's not on the root file system).
I use only 6 apps, and the appsdata folder is only about 7.5 GB. Is it normal that the /var/lib/docker/overlay2 takes up twice as much space as my appsdata? My understanding is that that folder contains the docker containers of the apps and whatever other containers are running, so it seems odd that it's that much larger than appsdata.
Is it possible that some old content is not cleaned up or duplicated when the VPS is rebooted? I had to reboot a few days ago (for the first time in months), just wondering if that has any connection. It was a hard reboot, i.e. equivalent to just cutting the power without shutting down.