title: What is hadoop (single and multi) nodes, spark-master and spark-worker?
body: <p>I want to understand the following terms:</p>
  
  <p>hadoop (single-node and multi-node)
  spark master
  spark worker
  namenode
  datanode</p>
  
  <p>What I understood so far is spark master is the job executor and handles all the spark workers. Whereas hadoop is the hdfs (where our data resides) and from where spark workers reads data according to the job given to them. Please correct me if I wrong.</p>
  
  <p>I also want to understand the role of namenode and datanode. Though I know the role of namenode (having the metadata info of all datanodes and it should be only one preferably, but could be two) and datanodes could be multiple and having the data.</p>
  
  <p>Are datanodes the same hadoop nodes?</p>