In order to have properly functioning infrastructure, it would be useful to have a proper set of roles for managing the backup servers and clients.

The solution should be based on Duplicity (http://duplicity.nongnu.org/) and Duply (http://duply.net/) - as convenient wrapper around duplicity.

There are two roles that should be implemented:
* backup_server
* backup_client

The '''backup_server''' role should be implemented as follows:
* Deploy Duplicity and Duply.
* Create users, based on a list servers, that will be allowed to backup to the server.
* Set-up authorized_keys for the backup users. Public keys should be provided locally.
* The backup users should be allowed sftp only, and should also be confined via chroot.

The '''backup_client''' role should be implemented as follows:
* Deploy Duplicity and Duply.
* Deploy a private key for logging-in into the backup server.
* Configure Duply, having it read exclude patterns from a single file.
* Design it so that exclude pattern file should be constructed using assemble module. Roles that want to create backups can simply deploy their exclude pattern file in this directory. Handler should be provided for reassembling this file.
* known_hosts should be populated appropriately from Ansible facts (check how) so the backups could be run automatically. This should be put into global known_hosts file.
* Configures cron-job for running backups (make this configurable).