Discourse upgrade fails due to insufficient disk space on 25G droplet

[Falco]

Considering

@AndyBr

root@DO-Discourse:/var/discourse# docker images
REPOSITORY            TAG       IMAGE ID       CREATED        SIZE
local_discourse/app   latest    3dac608caa92   4 months ago   3.17GB

and

@AndyBr

root@DO-Discourse:/var/discourse# du -h -s /var/lib/docker/overlay2/* | sort -h -r
8.7G    /var/lib/docker/overlay2/d319d95263d87c2a75a4bc9a9f03a25ea7f6eb1f7bac687e7ae7d45522939dc0
2.8G    /var/lib/docker/overlay2/79be56509f1588c272683332ef50abd54f0aeb06d0e2d13f8eea1bace3b3db46
873M    /var/lib/docker/overlay2/5b148cbbcca894be512c7407568104cd7b2e3d48ab7b7d74c6c0f731806cdddc

I think you have some dangling layers on your overlay2 folder.

See this StackOverflow answer for guidance:

Is it safe to clean docker/overlay2/