While starting the worker node I get the following error :
Spark Command: /usr/lib/jvm/default-java/bin/java -cp /home/ubuntu/spark-1.5.1-bin-hadoop2.6/sbin/
I'm afraid your hostname may be invalid to Spark, and you hava to change your spark-env.sh.
You can set the variable SPARK_MASTER_IP to be the real ip of master, instead of its hostname. e.g.
export SPARK_MASTER_IP=1.70.44.5
INSTEAD OF
export SPARK_MASTER_IP=ip-1-70-44-5