Metrics
Mind the gap.
The metrics-servlet module provides a handful of useful servlets:
HealthCheckServlet responds to GET requests by running all the [health checks](#health-checks) and returning 501 Not Implemented if no health checks are registered, 200 OK if all pass, or 500 Internal Service Error if one or more fail. The results are returned as a human-readable text/plain entity.
If the servlet context has an attributed named com.yammer.metrics.reporting.HealthCheckServlet.registry which is a HealthCheckRegistry, HealthCheckServlet will use that instead of the default HealthCheckRegistry.
ThreadDumpServlet responds to GET requests with a text/plain representation of all the live threads in the JVM, their states, their stack traces, and the state of any locks they may be waiting for.
MetricsServlet exposes the state of the metrics in a particular registry as a JSON object.
If the servlet context has an attributed named com.yammer.metrics.reporting.MetricsServlet.registry which is a MetricsRegistry, MetricsServlet will use that instead of the default MetricsRegistry.
MetricsServlet also takes an initialization parameter, show-jvm-metrics, which if "false" will disable the outputting of JVM-level information in the JSON object.
PingServlet responds to GET requests with a text/plain/200 OK response of pong. This is useful for determining liveness for load balancers, etc.
AdminServlet aggregates HealthCheckServlet, ThreadDumpServlet, MetricsServlet, and PingServlet into a single, easy-to-use servlet which provides a set of URIs: