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Use bind mounts instead of docker volumes. Then you just have normal directories to back up, the same as you would anything else.
In general, it's not a problem to back up files while the container is running. The exception to this is databases. To have reliable database backups, you need to stop the container (or quiesce/pause the database if it supports it) before backing up the raw database files (including SQLite).
This is your answer. It also has the benefit of allowing you to have a nice folder structure for your Docker setup, where you have a folder for each service holding the corresponding compose yaml and data folder(s)
Rsync works fine for most data. (I use borgbackup) For any database data, create a dump using pg_dump or mysqldump or whatever. Then backup the dump and all other volumes but exclude the db volume.
You can copy data from docker volumes to somewhere on the host node to do the backup from there. You can also have a container using the volumes and from there you can send directly to remote, or map a dorectory on the host node to copy the files to.
If you are running a database or something stateful, look at best practices for backup and then adjust to it.
Or not use volumes and map onto the host node directly. each works, and had its own advantages/disadvantages.
Bind mounts are easy to maintain and backup. However if you share data amongst multiple container docker volumes are recommend especially for managing state.
Backup volumes:
docker run --rm --volumes-from dbstore -v $(pwd):/backup containername tar cvf /backup/backup.tar /dbdata
Database volume backup without stopping the service: bash into the container, dump it, and copy it out with docker cp. Run it periodically via crontab