diff --git a/docs/deployment/pull-backup.rst b/docs/deployment/pull-backup.rst index ce593cdb7..a29ee8188 100644 --- a/docs/deployment/pull-backup.rst +++ b/docs/deployment/pull-backup.rst @@ -422,3 +422,83 @@ Parentheses are not needed when using a dedicated bash process. ``kill "${SSH_AGENT_PID}"`` Kill ssh-agent with loaded keys when it is not needed anymore. + +Remote forwarding +================= + +The standard ssh client allows to create tunnels to forward local ports to a remote server (local forwarding) and also +to allow remote ports to be forwarded to local ports (remote forwarding). + +This remote forwarding can be used to allow remote backup clients to access the backup server even if the backup server +cannot be reached by the backup client. + +This can even be used in cases where neither the backup server can reach the backup client and the backup client cannot +reach the backup server, but some intermediate host can access both. + +A schematic approach is as follows + +:: + + Backup Server (backup@mybackup) Intermediate Machine (john@myinter) Backup Client (bob@myclient) + + 1. Establish SSH remote forwarding -----------> SSH listen on local port + + 2. Starting ``borg create`` establishes + 3. SSH forwards to intermediate machine <------- SSH connection to the local port + 4. Receives backup connection <------- and further on to backup server + via SSH + +So for the backup client the backup is done via SSH to a local port and for the backup server there is a normal backup +performed via ssh. + +In order to achieve this, the following commands can be used to create the remote port forwarding: + +1. On machine ``myinter`` + +``ssh bob@myclient -v -C -R 8022:mybackup:22 -N`` + +This will listen for ssh-connections on port ``8022`` on ``myclient`` and forward connections to port 22 on ``mybackup``. + +You can also remove the need for machine ``myinter`` and create the port forwarding on the backup server directly by +using ``localhost`` instead of ``mybackup`` + +2. On machine ``myclient`` + +``borg create -v --progress --stats ssh://backup@localhost:8022/home/backup/repos/myclient /`` + +Make sure to use port ``8022`` and ``localhost`` for the repository as this instructs borg on ``myclient`` to use the +remote forwarded ssh connection. + +SSH Keys +~~~~~~~~ + +If you want to automate backups when using this method, the ssh ``known_hosts`` and ``authorized_keys`` need to be set up +to allow connections. + +Security Considerations +~~~~~~~~~~~~~~~~~~~~~~~ + +Opening up SSH access this way can pose a security risk as it effectively opens remote access to your +backup server on the client even if it is located outside of your company network. + +To reduce the chances of compromise, you should configure a forced command in ``authorized_keys`` to prevent +anyone from performing any other action on the backup server. + +This can be done e.g. by adding the following in ``$HOME/.ssh/authorized_keys`` on ``mybackup`` with proper +path and client-fqdn: + +:: + + command="cd /home/backup/repos/;borg serve --restrict-to-path /home/backup/repos/" + + +All the additional security considerations for borg should be applied, see :ref:`central-backup-server` for some additional +hints. + +More information +~~~~~~~~~~~~~~~~ + +See `remote forwarding`_ and the `ssh man page`_ for more information about remote forwarding. + + .. _remote forwarding: https://linuxize.com/post/how-to-setup-ssh-tunneling/ + .. _ssh man page: https://manpages.debian.org/testing/manpages-de/ssh.1.de.html