Monitor and Debug NATS
It is easy to monitor the NATS server. When the monitoring port is enabled, the NATS server runs a lightweight web server on port 8222 with has several endpoints that return JSON objects.
1. In a terminal, CD to the NATS server directory.
2. Start the NATS server with monitoring enabled.
gnatsd -m 8222
3. Verify that the NATS server starts with the HTTP monitor on port 8222.
 2015/08/19 20:09:58.572939 [INF] Starting gnatsd version 0.6.4  2015/08/19 20:09:58.573007 [INF] Starting http monitor on port 8222  2015/08/19 20:09:58.573071 [INF] Listening for client connections on 0.0.0.0:4222  2015/08/19 20:09:58.573090 [INF] gnatsd is ready
4. Explore the monitoring endpoints.
The endpoint http://localhost:8222/varz reports various general statistics. If you run a subscriber and refresh the endpoint, you see that the number of connections changes from 0 to 1.
The endpoint http://localhost:8222/connz show details about the connections. Launch a publisher and refresh the endpoint to see the statistics. The http://localhost:8222/varz shows the number of messages processed by the server.
Launch another subscriber and check out the http://localhost:8222/subscriptionsz endpoint. You’ll see that there are two subscribers. Publish more messages and monitor the results using the various endpoints. The http://localhost:8222/routez endpoint shows the current routes.