Hi, DSS needs to make lots of connections to be useful, and to manage that in a docker environment needs to be carefully evaluated in term of cost/benefit.
Perhaps you could explain why docker is part of your use case. If there is no compelling reason to use docker, you may be better off installing DSS directly.
You can use docker cp to actually copy the backup data within the container
But more probably, you may want to mount the DSS data directory as an external volume which would be backed up - this is documented in our Dockerhub page - in that case, you can use the backup as this external directory.
On a side note:
It's possible to have several instances of DSS on one machine, especially if you keep the data directories mapped one-to-one to your instances. If you let different instances of DSS manipulate your DATADIR, it could be messy (version conflicts, for example).