trapperkeeper-metrics currently configures the Jolokia service with debug logging enabled by default:
However, this setting unfortunately does more than just providing access to DEBUG-level messages. It also causes some things to be logged at ERROR level, like backtraces for "missing" JMX items that should just result in a 404 message (
Having Jolokia in debug mode by default gives access to information that can be useful, but logging stack traces for "normal" 404s means that information is coming at a cost of a drastically lowered signal-to-noise ratio in the logs.
I can't recall an incident where we needed to debug Jolokia in the past couple years, so it's likely a good trade-off to just shut debug off by default and enable it in metrics.conf when needed.