File synchronization

Tools to synchronize data and so called clouds are pretty handy to use files on
different machines.
There are tools with a main server and there are tools that don't need them.

Synchronizing with server

The biggest advantage of having a main server contain your data is that - as
long as the server is online -
you can sync as you please.
You do not need to care which machines are online to get all the files you need.
If you are talking about a cloud, this is this.

• Owncloud is a self-hostable, open-source file hosting service
  that can be dockerized.

Synchronizing without server

If you can bare the difficulties ascending due to the mentioned above problems,
this is probably a more
safe way to "host" files.
There is no single server as point of attack with all your data.

• Syncthing is a free and open-source peer-to-peer file
  synchronization tool that can be dockerized.