/var/lib/docker/overlay2 growing until all disk space is consumed

[cpswan]

Describe the bug

I just logged into my dess VM to do some testing and found that the 16GB (virtual) disk is full :0

Output from df -h:

Filesystem      Size  Used Avail Use% Mounted on
udev            447M     0  447M   0% /dev
tmpfs            99M  1.4M   97M   2% /run
/dev/sda2        16G   15G     0 100% /
tmpfs           491M     0  491M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           491M     0  491M   0% /sys/fs/cgroup
/dev/loop1       74M   74M     0 100% /snap/lxd/21624
/dev/loop2      100M  100M     0 100% /snap/core/11798
/dev/loop3       62M   62M     0 100% /snap/core20/1169
/dev/loop4       62M   62M     0 100% /snap/core20/1081
/dev/loop5       56M   56M     0 100% /snap/core18/2128
/dev/loop6       43M   43M     0 100% /snap/certbot/1434
/dev/loop7       73M   73M     0 100% /snap/lxd/21723
/dev/loop8       56M   56M     0 100% /snap/core18/2074
/dev/loop0      100M  100M     0 100% /snap/core/11993
/dev/loop9       33M   33M     0 100% /snap/snapd/13270
/dev/loop10      43M   43M     0 100% /snap/certbot/1514
tmpfs            99M     0   99M   0% /run/user/1000
/dev/loop12      33M   33M     0 100% /snap/snapd/13640
overlay          16G   15G     0 100% /var/lib/docker/overlay2/4d66517aebe5ce15982bbfd713e2087ed1a7813cce169d1ce2fa79cdb9e724a3/merged
overlay          16G   15G     0 100% /var/lib/docker/overlay2/e3aa4b55e280fa22fb0a857b797d27b4014da1e150b0f4553b137e88465efbcf/merged

Output from du -aBM 2>/dev/null | sort -nr | head -n 50 | more:

18430M  .
9958M   ./var
8555M   ./var/lib
7267M   ./var/lib/docker
7117M   ./var/lib/docker/overlay2
3380M   ./usr
2354M   ./snap
2315M   ./usr/lib
1963M   ./swap.img
1310M   ./var/log
1297M   ./var/log/journal/3e3b84c1a6a94203a69ab2e7631c3a4c
1297M   ./var/log/journal
1116M   ./var/lib/snapd
837M    ./usr/lib/modules
780M    ./var/lib/docker/overlay2/4d66517aebe5ce15982bbfd713e2087ed1a7813cce169d1ce2fa79cdb9e724a3/merged
780M    ./var/lib/docker/overlay2/4d66517aebe5ce15982bbfd713e2087ed1a7813cce169d1ce2fa79cdb9e724a3
729M    ./var/lib/snapd/snaps
658M    ./var/lib/docker/overlay2/4d66517aebe5ce15982bbfd713e2087ed1a7813cce169d1ce2fa79cdb9e724a3/merged/usr
618M    ./var/lib/docker
618M    ./var/lib/docker/overlay2/5dbb503e88cebf69c10a8ba82727dd6c58bf22bf0f5b9f0ac42962a14b8eb5c3
610M    ./var/lib/docker/overlay2/5dbb503e88cebf69c10a8ba82727dd6c58bf22bf0f5b9f0ac42962a14b8eb5c3/diff/usr
605M    ./var/lib/docker/overlay2/4d66517aebe5ce15982bbfd713e2087ed1a7813cce169d1ce2fa79cdb9e724a3/merged/usr/lib
596M    ./snap/core
577M    ./var/lib/docker/overlay2/5dbb503e88cebf69c10a8ba82727dd6c58bf22bf0f5b9f0ac42962a14b8eb5c3/diff/usr/lib
572M    ./var/lib/docker/overlay2/d71f0b166ea31f16c7874be444f227700598ea4dee1d5310ab77ef22450822bd/diff
572M    ./var/lib/docker/overlay2/d71f0b166ea31f16c7874be444f227700598ea4dee1d5310ab77ef22450822bd
572M    ./var/lib/docker/overlay2/cdf121468c4fd0c75b8582096e2a70bfbab6a23382dfe334b346b22705c6dd3f/diff
572M    ./var/lib/docker/overlay2/cdf121468c4fd0c75b8582096e2a70bfbab6a23382dfe334b346b22705c6dd3f
572M    ./var/lib/docker/overlay2/86ad0160354761a010cc1a9785bb9d05032d0cd999111ee4eee50de8e489479c/diff
572M    ./var/lib/docker/overlay2/86ad0160354761a010cc1a9785bb9d05032d0cd999111ee4eee50de8e489479c
572M    ./var/lib/docker/overlay2/0a44c6269b670bb8583bd57ed48fa215deff5a1a95c03f58d0c9c20476ef5dc5/diff

To Reproduce
Steps to reproduce the behavior:

1. Create a fresh VM
2. Install dess
3. Install a few @ signs
4. Wait a few weeks

Expected behavior
Disk doesn't fill up (so quickly)

Additional context

This is something of a known issue with Docker, but given that the secondary is small it shouldn't be creating such huge filesystem growth.