Logstash data ouput to elasticsearch calculation


I am trying to find out how to see how much data is being outputted to elasticsearch from logstash servers. The logstash servers in question are hosted on VMWare at the moment.

The logstash server hosted on AWS, I can see how much data is coming out on the networkout within cloudwatch metrics.

How can I get a similar result on the logstash boxes themselves?
Many thanks.