Packetbeat is an open source network packet analyzer that ships the data to Elasticsearch. Think of it like a distributed real-time Wireshark with a lot more analytics features.
The Packetbeat shippers sniff the traffic between your application processes, parse on the fly protocols like HTTP, MySQL, PostgreSQL, Redis or Thrift and correlate the messages into transactions.
For each transaction, the shipper inserts a JSON document into Elasticsearch, where it is stored and indexed. You can then use Kibana to view key metrics and do ad-hoc queries against the data.
To learn more about Packetbeat, check out https://www.elastic.co/products/beats/packetbeat.
Please visit elastic.co for the documentation.