title: OpenMPI node & network topology
body: <p>i am currently building a small utility library as part of a larger project.
  OpenMPI has a well documented API library but i am a little puzzled when it comes to the lower level communication between nodes.
  I know that when writing your algorithm, you distribute it across all nodes that are expected to do the computation each communicating with the rest, executing portion of the algorithm based on their "global" MPI rank (as defined in the algorithm), and all the nodes synchronize back and forth. However, the reason i placed global in quotes is, does openMPI communicate on the ip level, hence say that i already have a long executing algorithm, but there is a node that is idling, not running any MPI processes, if i execute my MPI algorithm on it, will it join the MPI_COMM_WORLD and become part of the overall network topology or is there some "voodoo" i need to do to make that node part of the MPI_COMM_WORLD.
  also, if nodes can become part of MPI_COMM_WORLD for that particular algorithm, how can i register/identify this new node?</p>
  
  <p>any reading references are also helpful.</p>
  
  <p>many thanks!</p>
  
  <p>tl;dr are MPI nodes hot-swappable from the MPI_COMM_WORLD?</p>