A New Relic (NR) plugin for monitoring the health of Dropwizard
applications over http using the application Health Check exposed
on the admin port at /healthcheck.
It does not collect Dropwizard /metrics data or otherwise provide instrumentation of the JVM or server. It provides
a mechanism to monitor and alert on the health of Dropwizard applications.
For collecting general JVM metrics and application transactions, consider installing New Relic's Java Agent. For collecting Dropwizard-specific metrics into New Relic, consider using the [metrics-new-relic] (https://github.com/palominolabs/metrics-new-relic) library.
This plugin provides the ability to send NR alerts based on the Dropwizard application's /healthcheck response and
records historical data within NR on which health check(s) failed. The overall status of the /healthcheck response,
the status code returned, and the states of the individual health checks are recorded.
Since NR does not support any text values or annotation of metric values, it's impossible to capture health check messages within NR.
Multiple Dropwizard applications can be monitored from the same plugin instance. The plugin polls all configured Dropwizard applications every minute and publishes the appropriate data into NR. The plugin handles failures to connect to or receive a response from a Dropwizard application; only applications that provide a valid 200 status code response are considered healthy.
This plugin is available in Plugin Central and is NPI-compliant and can be [installed using NPI] (https://docs.newrelic.com/docs/plugins/plugins-new-relic/installing-plugins/installing-npi-compatible-plugin).
npi install com.cafepress.newrelic.plugin.dropwizard
Additionally, New Relic has [documentation for doing it the Chef or Puppet way] (https://docs.newrelic.com/docs/plugins/plugins-new-relic/installing-plugins/plugin-installation-chef-and-puppet).
The New Relic Platform does not natively support boolean metric values and this plugin represents boolean values using 0 (false) and 1 (true). Conceptually, [this is somewhat problematic] (https://discuss.newrelic.com/t/how-to-report-yes-no-boolean-values-via-a-custom-plugin/4990/6) but, in practice, it mostly works. Because the boolean values are treated as numbers and subject to aggregation, the NR dashboard UI can occasionally report unexpected "boolean" values that are fractional. We have not seen this lead to false alerting but it can be confusing if you're not aware of it.
Additionally, although NR is in the [process of revamping their alerting system] (https://docs.newrelic.com/docs/alerts/new-relic-alerts-beta/getting-started/alerting-new-relic), NR's current support for alerting on Plugin data is limited. Specifically, it only supports sending notifications when the value of some metric exceeds a specified threshold. Alerting on values of 0 (or on the absence of data) is not possible.
The approach this plugin takes is to publish an "unhealthiness" metric as a boolean value into NR and to then alert when the threshold of the "unhealthiness" metric is greater than some very small value (eg 0.001). In practice, this delivers what you want: NR sends an alert whenever the application is unhealthy -- as with most NR alerts, there's a several minute lag after the application recovers before NR recovers to prevent excessive alerting in the case of a flagging metric.
In addition to the overall "unhealthiness" metric, the plugin publishes individual "healthiness" metrics and a http status code metric for visualization within the UI.