Merge pull request #1011 from pnerg/distributions-as-gauges

(prometheus) Added the possibility to generate gauge metrics from distribution based metrics

reporters/kamon-prometheus/src/main/resources/reference.conf

@@ -60,7 +60,7 @@ kamon.prometheus {
   }
 
   summaries {
-    # Names of the histogram, timer and range sampler metrics that must be exported as summaries. All patterns are treared as Glob patterns.
+    # Names of the histogram, timer and range sampler metrics that must be exported as summaries. All patterns are treated as Glob patterns.
     metrics = [
       # example:
       # "request*",
@@ -77,6 +77,17 @@ kamon.prometheus {
     ]
   }
 
+  gauges {
+    # Names of the histogram, timer and range sampler metrics that shall be exported as a gauges as well.
+    # For each matching metric there will be three gauges representing the current seen distribution (min, max, avg)
+    # All patterns are treated as Glob patterns.
+    metrics = [
+      # example:
+      # "http.server*",
+      # "*akka*"
+    ]
+  }
+
   embedded-server {
 
     # Hostname and port used by the embedded web server to publish the scraping enpoint.

reporters/kamon-prometheus/src/main/scala/kamon/prometheus/PrometheusReporter.scala

@@ -62,6 +62,7 @@ class PrometheusReporter(configPath: String = DefaultConfigPath, initialConfig:
 
     scrapeDataBuilder.appendCounters(currentData.counters)
     scrapeDataBuilder.appendGauges(currentData.gauges)
+    scrapeDataBuilder.appendDistributionMetricsAsGauges(snapshot.rangeSamplers ++ snapshot.histograms ++ snapshot.timers)
     scrapeDataBuilder.appendHistograms(currentData.histograms)
     scrapeDataBuilder.appendHistograms(currentData.timers)
     scrapeDataBuilder.appendHistograms(currentData.rangeSamplers)

reporters/kamon-prometheus/src/main/scala/kamon/prometheus/PrometheusSettings.scala

@@ -31,14 +31,17 @@ object PrometheusSettings {
     informationBuckets: Seq[java.lang.Double],
     customBuckets: Map[String, Seq[java.lang.Double]],
     includeEnvironmentTags: Boolean,
-    summarySettings: SummarySettings
+    summarySettings: SummarySettings,
+    gaugeSettings: GaugeSettings
   )
 
   case class SummarySettings(
     quantiles: Seq[java.lang.Double],
     metricMatchers: Seq[Glob]
   )
 
+  case class GaugeSettings(metricMatchers: Seq[Glob])
+
   def readSettings(prometheusConfig: Config): Generic = {
     Generic(
       defaultBuckets = prometheusConfig.getDoubleList("buckets.default-buckets").asScala.toSeq,
@@ -49,6 +52,9 @@ object PrometheusSettings {
       summarySettings = SummarySettings(
         quantiles = prometheusConfig.getDoubleList("summaries.quantiles").asScala.toSeq,
         metricMatchers = prometheusConfig.getStringList("summaries.metrics").asScala.map(Glob).toSeq
+      ),
+      gaugeSettings = GaugeSettings(
+        metricMatchers = prometheusConfig.getStringList("gauges.metrics").asScala.map(Glob).toSeq
       )
     )
   }

reporters/kamon-prometheus/src/main/scala/kamon/prometheus/ScrapeDataBuilder.scala

@@ -19,8 +19,7 @@ package kamon.prometheus
 import java.lang.StringBuilder
 import java.text.{DecimalFormat, DecimalFormatSymbols}
 import java.util.Locale
-
-import kamon.metric.{Distribution, MeasurementUnit, MetricSnapshot}
+import kamon.metric.{Distribution, Instrument, MeasurementUnit, Metric, MetricSnapshot}
 import kamon.metric.MeasurementUnit.{information, time}
 import kamon.metric.MeasurementUnit.Dimension._
 import kamon.tag.TagSet
@@ -50,6 +49,39 @@ class ScrapeDataBuilder(prometheusConfig: PrometheusSettings.Generic, environmen
     this
   }
 
+  def appendDistributionMetricsAsGauges(distributions: Seq[MetricSnapshot.Distributions]): ScrapeDataBuilder = {
+    def gaugeFilter(metric:MetricSnapshot.Distributions):Boolean = prometheusConfig.gaugeSettings.metricMatchers.exists(_.accept(metric.name))
+    def avg(snap:Instrument.Snapshot[Distribution]):Double = if(snap.value.count == 0) 0 else snap.value.sum/snap.value.count
+
+    distributions
+      .filter(gaugeFilter)
+      .map{ metric =>
+        val settings = Metric.Settings.ForValueInstrument(metric.settings.unit, metric.settings.autoUpdateInterval)
+        Seq(
+          MetricSnapshot.ofValues(
+            name = metric.name+".min",
+            description = metric.description,
+            settings = settings,
+            instruments = metric.instruments.map(snap => Instrument.Snapshot[Double](snap.tags, snap.value.min.toDouble))
+          ),
+          MetricSnapshot.ofValues(
+            name = metric.name+".max",
+            description = metric.description,
+            settings = settings,
+            instruments = metric.instruments.map(snap => Instrument.Snapshot[Double](snap.tags, snap.value.max.toDouble))
+          ),
+          MetricSnapshot.ofValues(
+            name = metric.name+".avg",
+            description = metric.description,
+            settings = settings,
+            instruments = metric.instruments.map(snap => Instrument.Snapshot[Double](snap.tags, avg(snap)))
+          )
+        )
+    }.flatten
+     .foreach(appendGaugeMetric)
+    this
+  }
+
   private def appendCounterMetric(metric: MetricSnapshot.Values[Long]): Unit = {
     val unit = metric.settings.unit
     val normalizedMetricName = normalizeCounterMetricName(metric.name, unit)

reporters/kamon-prometheus/src/test/scala/kamon/prometheus/ScrapeDataBuilderSpec.scala

@@ -3,7 +3,7 @@ package kamon.prometheus
 import com.typesafe.config.ConfigFactory
 import kamon.metric.MeasurementUnit.{information, none, time}
 import kamon.metric.{MeasurementUnit, MetricSnapshot}
-import kamon.prometheus.PrometheusSettings.SummarySettings
+import kamon.prometheus.PrometheusSettings.{GaugeSettings, SummarySettings}
 import kamon.tag.TagSet
 import kamon.testkit.MetricSnapshotBuilder
 import kamon.util.Filter.Glob
@@ -320,6 +320,43 @@ class ScrapeDataBuilderSpec extends WordSpec with Matchers {
 
     }
 
+    "append gauges only for matching metrics" in {
+      val histogramWithHundredEntries = constantDistribution("firstMetric", none, 1, 100)
+      val histogramWithHundredEntriesTwo = constantDistribution("secondMetric", none, 1, 100)
+      val result = builder(withGauges = Seq("first*"))
+        .appendDistributionMetricsAsGauges(Seq(histogramWithHundredEntries, histogramWithHundredEntriesTwo))
+        .build()
+      println(result)
+      result should include {
+        """|# TYPE firstMetric_min gauge
+           |firstMetric_min 1.0
+           |""".stripMargin
+      }
+      result should include {
+        """|# TYPE firstMetric_max gauge
+           |firstMetric_max 100.0
+           |""".stripMargin
+      }
+      result should include {
+        """|# TYPE firstMetric_avg gauge
+           |firstMetric_avg 50.0
+           |""".stripMargin
+      }
+
+      result should not include {
+        """|# TYPE secondMetric_min gauge
+           |""".stripMargin
+      }
+      result should not include {
+        """|# TYPE secondMetric_max gauge
+           |""".stripMargin
+      }
+      result should not include {
+        """|# TYPE secondMetric_avg gauge
+           |""".stripMargin
+      }
+    }
+
     "include global custom tags from the Kamon.environment.tags" in {
       val counterOne = MetricSnapshotBuilder.counter("counter-one", "", TagSet.of("tag.with.dots", "value"), time.seconds, 10)
       val gaugeOne = MetricSnapshotBuilder.gauge("gauge-one", "", TagSet.Empty, time.seconds, 20)
@@ -358,15 +395,17 @@ class ScrapeDataBuilderSpec extends WordSpec with Matchers {
   private def builder(buckets: Seq[java.lang.Double] = Seq(5D, 7D, 8D, 9D, 10D, 11D, 12D),
                       customBuckets: Map[String, Seq[java.lang.Double]] = Map("histogram.custom-buckets" -> Seq(1D, 3D)),
                       environmentTags: TagSet = TagSet.Empty,
-                      withSummary: Seq[String] = Seq.empty) = {
+                      withSummary: Seq[String] = Seq.empty,
+                      withGauges: Seq[String] = Seq.empty) = {
     new ScrapeDataBuilder(
       PrometheusSettings.Generic(
         buckets,
         buckets,
         buckets,
         customBuckets,
         false,
-        SummarySettings(Seq(0.5, 0.75, 0.95, 0.99), withSummary.map(Glob))),
+        SummarySettings(Seq(0.5, 0.75, 0.95, 0.99), withSummary.map(Glob)),
+        GaugeSettings(withGauges.map(Glob))),
       environmentTags
     )
   }