To use this Apache Druid extension, include prometheus-emitter in the extensions load list.

Introduction

This extension exposes Druid metrics for collection by a Prometheus server (https://prometheus.io/). Emitter is enabled by setting druid.emitter=prometheus configs or include prometheus in the composing emitter list.

Configuration

All the configuration parameters for the Prometheus emitter are under druid.emitter.prometheus.

propertydescriptionrequired?default
druid.emitter.prometheus.strategyThe strategy to expose prometheus metrics. Default strategy exporter would expose metrics for scraping purpose. Only peon task (short-lived jobs) need to use pushgateway strategy.yesexporter
druid.emitter.prometheus.portThe port on which to expose the prometheus HTTPServer. Required if using exporter strategy.nonone
druid.emitter.prometheus.namespaceOptional metric namespace. Must match the regex [a-zA-Z:][a-zA-Z0-9:]*no“druid”
druid.emitter.prometheus.dimensionMapPathJSON file defining the Prometheus metric type, desired dimensions, help text, and conversionFactor for every Druid metric.noDefault mapping provided. See below.
druid.emitter.prometheus.pushGatewayAddressPushgateway address. Required if using Pushgateway strategynonone

Metric names

All metric names and labels are reformatted to match Prometheus standards.

  • For names: all characters which are not alphanumeric, underscores, or colons (matching [^a-zA-Z_:][^a-zA-Z0-9_:]*) are replaced with _
  • For labels: all characters which are not alphanumeric or underscores (matching [^a-zA-Z0-9_][^a-zA-Z0-9_]*) are replaced with _

Metric mapping

Each metric to be collected by Prometheus must specify a type, one of [timer, counter, guage]. Prometheus Emitter expects this mapping to be provided as a JSON file. Additionally, this mapping specifies which dimensions should be included for each metric. Prometheus expects histogram timers to use Seconds as the base unit. Timers which do not use seconds as a base unit can use the conversionFactor to set the base time unit. If the user does not specify their own JSON file, a default mapping is used. All metrics are expected to be mapped. Metrics which are not mapped will not be tracked. Prometheus metric path is organized using the following schema: <druid metric name> : { "dimensions" : <dimension list>, "type" : <timer|counter|gauge>, conversionFactor: <conversionFactor>, "help" : <help text>,} e.g. query/time" : { "dimensions" : ["dataSource", "type"], "conversionFactor": 1000.0, "type" : "timer", "help": "Seconds taken to complete a query."}

For metrics which are emitted from multiple services with different dimensions, the metric name is prefixed with the service name. e.g. "coordinator-segment/count" : { "dimensions" : ["dataSource"], "type" : "gauge" }, "historical-segment/count" : { "dimensions" : ["dataSource", "tier", "priority"], "type" : "gauge" }

For most use-cases, the default mapping is sufficient.