Creating a SSH tunnel using OpenSSH¶
A ssh key pair, properly installed in your VSC account, see the page on generating keys.
Additionally, you should be able to connect to the cluster’s login node using ssh.
Because of one or more firewalls between your desktop and the HPC clusters, it is generally impossible to communicate directly with a process on the cluster from your desktop except when the network managers have given you explicit permission (which for security reasons is not often done). One way to work around this limitation is SSH tuneling. There are serveral cases where this is usefull:
Running X applications on the cluster: The X program cannot directly communicate with the X server on your local system. In this case, the tunneling is easy to set up as OpenSSH will do it for you if you specify the -X-option on the command line when you log on to the cluster in text mode:
$ ssh -X <vsc-account>@<vsc-loginnode>
where <vsc-account> is your VSC-number and <vsc-loginnode> is the hostname of the cluster’s login node you are using.
Running a server application on the cluster that a client on the desktop connects to. One example of this scenario is ParaView in remote visualization mode, with the interactive client on the desktop and the data processing and image rendering on the cluster. Setting up a tunnel for this scenario is also explained on that page.
Running clients on the cluster and a server on your desktop. In this case, the source port is a port on the cluster and the destination port is on the desktop.
In a terminal window on your client machine, issue the following command:
ssh -L11111:r1i3n5:44444 -N <vsc-account>@<vsc-loginnode>
where <vsc-account> is your VSC-number and <vsc-loginnode> is the hostname of the cluster’s login node you are using. The local port is given first (e.g., 11111, followed by the remote host (e.g., ‘r1i3n5’) and the server port (e.g., 44444).
Log in on the login node
Start the server job, note the compute node’s name the job is running on (e.g., ‘r1i3n5’), as well as the port the server is listening on (e.g., ‘44444’).