How-To use VisIt on JURECA

Hardware Setup

The following image illustrates the general JURECA hardware setup used in a distributed visualisation session.
The user has its own workstation, which acts as a frontend to setup the visualisation pipeline and to adjust parameters of the visualisation process. Of course also the rendered image is shown on the users workstation.
The right side illustrates the major components of the JURECA cluster: login, compute and visualisation nodes and the GPFS storage system (JUST), which holds the data to be visualised.
The user has access to the resources of JURECA only via an ssh connection to a login node. In between is a firewall which only allows access to the system by ssh (port 22). All other network ports are blocked. Therefore all communication related to the distributed visualisation environment has to be tunneled over ssh.

In general, a distributed visualisation package, like VisIt, consists of a viewer/GUI component and a parallel server/engine component. These software components can be mapped onto the hardware components in different ways. The three most commenly used scenarios are discussed in the following sections.

---

Remote Visualisation on a JURECA Vis Node

In this scenario only the VisIt viewer (GUI) is running on the users workstation. The data processing and image generation is performed by one or more VisIt engines (servers) running on one or more JURECA vis nodes. Like the compute nodes also the vis nodes have to be allocated by the JURECA batch system. That means that this visualisation scenario may not start instantly, if all vis nodes are already taken by other users! In this case one has to wait for free vis nodes. At the moment, the reservation of vis nodes, which would guarantee the access to vis nodes at a certain point in time is not yet possible. This feature is under development and will be available in the future.
All network traffic (e.g. sending images from the VisIt server to the viewer) runs across the login node and has to be tunneled. VisIt has a build in functionality to connect to the login node and to start the necessary batch job, so the user does not to need login manually to JURECA by an ssh shell and start batch jobs for VisIt there manually. Nevertheless VisIt uses ssh under the hood. Therefore an important prerequesite to get this scenario running is a flawless working ssh connectivity between the users workstation and JURECA! If a Windows operating system is used, it may be necessary to use a ssh key agent like Pageant, which is a part of the ​PuTTY ssh client for Windows.
In detail the following steps have to be performed:

1. Check ssh connectivity

Make sure that your workstation has ssh connectivity to the login nodes of JURECA. On a Linux workstation just check that you can login to JURECA with the regular ssh command.
On a Windows system one needs to install an ssh client first, e.g. ​PuTTY together with the ssh agent Pageant. Maybe you also want to install PuTTYgen to generate an ssh keys. Start Pageant and load your private ssh key into Pageant. Pageant will ask you for your passphrase, which unlocks the key. Now VisIt will be able to connect to JURECA using the (unlocked) private key stored in Pageant.

2. Install the correct version of VisIt on your local workstation

Download ​VisIt and install it on your workstation. Your local VisIt version must match the version installed on JURECA, which, as of today, is VisIt 2.10. So you have to install exactly VisIt 2.10 to get the setup running.

3. Create/import a host configuration for JURECA

To work in a distributed setup, VisIt needs information about the remote cluster and about how to launch processes on this cluster. These settings are called "Host profile" and can be adjusted in VisIt under Options --> Host profiles.
To keep thinks simple, we have created a predefined host profile for JURECA, which can be downloaded here​. Just download this file and, depending on your operatin system, copy it to:

• on a Linux system: ~/.visit/hosts
• on a Windows system: C:\Users\<username>\Documents\VisIt\hosts

After the successful installation of this file, start VisIt and open the host profile panel. You should find a host profile for JURECA now. The host profile has two launch profiles, one for launching the VisIt server on a vis node and another on for launching VisIt on compute nodes.

4. Connect VisIt to a JURECA login node

Start VisIt locally and click on "open file". A file browser pops up. Select JURECA as host. VisIt now establishes an ssh connection to JURECA, what may take some seconds. If everything works alright, you should see the filesystem of JURECA in the filebrowser now. Select the data you want to visualise.