There are a few ways to monitor flume in operation. We use the JSON reporting, which is available via 'http://<agent address>:<port>/metrics'. You need to start the agent with the following parameters to get this interface:
-Dflume.monitoring.type=http -Dflume.monitoring.port=34545
We use cacti to graph channel size both as a percentage of maximum and absolute number of events in channel. This provides warning if the sinks cannot keep up with the sources. 
We also graph ingress/egress event counts, much like a network bandwidth graph, for some channels to get an idea of the throughput and to see if sources/sinks are running at same speed.

From: liuyongbo []
Sent: Tuesday, May 14, 2013 10:38 PM
Subject: how to print the channel capacity


         I’m using flume to pass log data to mongodb, but I find that some data lose when the pressure is in high level, so I want to know the max request that flume can hold and need to print the capacity.but I can not find the proper way to do this instead of change the source code. Any ideas?