Is it possible to hot plug an additional node (host) into a working OpenMPI app? We’re talking about production environment where we cannot afford even a 5 second downtime.
There are two scenarios I’m interested in:
- We just would like to enhance the computing power by adding one more broadcast listener.
- A node died, the master node handles it well and reassigns the task to somebody else. The system administrator comes in, restarts the dead node and plugs it back into the cluster.
Which platform independent MPI implementation would be best for the scenario above? OpenMPI is not a must here.
MPI-2 — any implementation — does allow dynamic processes, and in fact adding processes is currently much more feasible than removing processes. You can use MPI_COMM_SPAWN to launch a new process with a given executable, and that returns an intracommunicator that can be used to communicate between the old (original) processes.
The tricks here are — nothing will automatically detect the new node. You’ll have to have some process keeping an eye out for them,
SPAWNsomething on them. If the new nodes will just be listeners to the master node, that’s probably the best case, as only the master node really needs to know about it. The invocation to ensure the spawn happens on the new node and not somewhere else will be done through theinfoargument to spawn, and may be implementation dependant.