The docker logs can grow quite a lot if not set in an /etc/docker/daemon.json file. Their (standard) path is:
/var/lib/docker/containers/<container_id>/<container_id>-json.log
So have a look there and delete files which are too big / too many.
Because I do not want the docker logs to grow indefinitely AND because I don't want docker to reside in a sub-sub-directory, I set as /etc/docker/daemon.json:
{
"data-root": "/docker/",
"log-driver": "json-file",
"log-opts": {
"max-size": "10m",
"max-file": "3"
}
}
The log-opts part set the max size of the logs. You should probably not use the data-root part, as you would need to stop the daelmon, move everything from /var/lib/docker to /docker and then start again. But the rest is usable.
40GB is really not much space. I would suggest a bigger VPS or RS. If you bought storage space, you need to mount that space before you can use it: https://www.netcup-wiki.de/wiki/Storagespace_mounten
You will probably still need to move your docker folder (if you have used volumes) to the NFS mount, so my daemon.json including the data-root part might still be useful for you. I would however highly recommend getting a bigger VPS or RS instead.