title: How can I check that my Spark Cluster do work?
body: <p>I have installed Spark 2.3.0 on Ubuntu 18.04 with two nodes: a master one (ip: 172.16.10.20) and a slave one (ip: 172.16.10.30). I can check that this Spark cluster looks like up and running</p>
  
  <pre><code>jps -lm | grep spark
  14165 org.apache.spark.deploy.master.Master --host 172.16.10.20 --port 7077 --webui-port 8080
  13701 org.apache.spark.deploy.worker.Worker --webui-port 8081 spark://172.16.10.20:7077
  </code></pre>
  
  <p>I give it a try with this simple R script (using the sparklyr package): </p>
  
  <pre><code>library(sparklyr)
  library(dplyr)
  # Set your SPARK_HOME path                                                                                                                                                       
  Sys.setenv(SPARK_HOME="/home/master/spark/spark-2.3.0-bin-hadoop2.7/")
  config &lt;- spark_config()
  # Optionally you can modify config parameters here                                                                                                                               
  
  sc &lt;- spark_connect(master = "spark://172.16.10.20:7077", spark_home = Sys.getenv("SPARK_HOME"), config = config)
  # Some test code, copying data to Spark cluster                                                                                                                                  
  iris_tbl &lt;- copy_to(sc, iris)
  src_tbls(sc)
  
  spark_apply(iris_tbl, function(data) {
     return(head(data))
  })
  </code></pre>
  
  <p>All commands are executed, fine and smooth (but a bit slow to my taste), and the spark log is kept in a temp file. When looking into the log file I see no mention of the slave node,  which makes me wonder, whether this Spark is really running in a cluster mode.</p>
  
  <p>How may I check that the master-slave relation is really working?</p>