Question

I’m a little confused regarding how a cluster implementation (“Beowulf cluster”) relates to a communication protocol such as MPI. What software components are needed to set up a “cluster” using something like OpenMPI?

Answer 1

A cluster, as you know, is a bunch of computers networked together. When you have such configuration, you normally install and use the following:

• MPI, for communication between processes
• NFS, to have a network disk visible and shared to all nodes
• NTP, to synchronize the time of the nodes so that you can compare log events and timestamps
• bootp to boot the nodes from a remote node, so that each node restart fresh with a guaranteed good and uniform setup.
• a set of cluster utilities to make your life easier, such as a distributed ssh to execute the same command on all nodes at the same time.
• a task scheduler, or queue manager, such as Condor, LFS or others, that allow you to prioritize job submissions and eventually measure them for limiting/pricing.
• a watchdog, so to reboot one node automatically if it gets stuck.
• software control for UPS (so to shut down automatically in case of prolonged loss of power)

And much more. All this stuff is completely additional to MPI. MPI is just a communication channel between processes. MPI alone does not “make the cluster”.