title: EMR Spark job using less executors than nodes in the cluster
body: <p>I have set up a testing cluster consisting of 1 m4large driver and 3 m4large nodes. Without adding any extra configuration arguments to <code>spark-submit</code> I wanted to test this cluster configuration. However, when I check in the Spark UI I can see that my Spark job only uses 2 executors and I also notice in Ganglia that one node is barely doing anything (like it's not used at all).</p>
  
  <p>What can I do to make sure that all nodes are getting tasks to complete?</p>