Merge pull request #625 from lenguyenthanh/prometheus-exporter

Improve Prometheus exporter

src/main/scala/Monitor.scala

@@ -29,7 +29,7 @@ final class Monitor(
     logger.info(s"lila-ws 3.0 netty kamon=$useKamon")
     logger.info(s"Java version: $version, memory: ${memory}MB")
 
-    if useKamon then kamon.Kamon.init()
+    if useKamon then kamon.Kamon.initWithoutAttaching()
 
     scheduler.scheduleWithFixedDelay(5.seconds, 1949.millis) { () => periodicMetrics() }
 

src/main/scala/util/PrometheusExporter.scala

@@ -0,0 +1,92 @@
+package lila.ws
+
+import com.typesafe.config.Config
+import kamon.Kamon
+import kamon.metric.*
+import kamon.module.{ MetricReporter, Module, ModuleFactory }
+import kamon.prometheus.*
+
+import java.time.Duration
+
+// copy paste with some minor changes/scalafmtAll from https://github.com/kamon-io/Kamon/blob/master/reporters/kamon-prometheus/src/main/scala/kamon/prometheus/PrometheusReporter.scala
+// unused http server has been removed
+class PrometheusReporter(configPath: String = DefaultConfigPath, initialConfig: Config = Kamon.config())
+    extends MetricReporter
+    with ScrapeSource:
+
+  import PrometheusReporter.readSettings
+  import kamon.prometheus.PrometheusSettings.environmentTags
+
+  private val stalePeriod = Duration.ofSeconds(2 * 24 * 60 * 60 + 1) // 2 days + 1 second
+  private val _snapshotAccumulator =
+    PeriodSnapshot.accumulator(stalePeriod, Duration.ZERO, stalePeriod)
+
+  @volatile private var _preparedScrapeData: String =
+    "# The kamon-prometheus module didn't receive any data just yet.\n"
+
+  @volatile private var _config           = initialConfig
+  @volatile private var _reporterSettings = readSettings(initialConfig.getConfig(configPath))
+
+  override def stop(): Unit =
+    // Removes a reference to the last reporter to avoid leaking instances.
+    //
+    // It might not be safe to assume that **this** object is the last created instance, but in practice
+    // users never have more than one instance running. If they do, they can handle access to their instances
+    // by themselves.
+    PrometheusReporter._lastCreatedInstance = None
+
+  override def reconfigure(newConfig: Config): Unit =
+    _reporterSettings = readSettings(newConfig.getConfig(configPath))
+    _config = newConfig
+
+  override def reportPeriodSnapshot(snapshot: PeriodSnapshot): Unit =
+    _snapshotAccumulator.add(snapshot)
+    val currentData = _snapshotAccumulator.peek()
+    val scrapeDataBuilder =
+      new ScrapeDataBuilder(_reporterSettings.generic, environmentTags(_reporterSettings.generic))
+
+    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)
+    _preparedScrapeData = scrapeDataBuilder.build()
+
+  def scrapeData(): String =
+    _preparedScrapeData
+
+object PrometheusReporter:
+
+  final val DefaultConfigPath = "kamon.prometheus"
+
+  /** We keep a reference to the last created Prometheus Reporter instance so that users can easily access it
+    * if they want to publish the scrape data through their own HTTP server.
+    */
+  @volatile private var _lastCreatedInstance: Option[PrometheusReporter] = None
+
+  /** Returns the latest Prometheus scrape data created by the latest PrometheusReporter instance created
+    * automatically by Kamon. If you are creating more than one PrometheusReporter instance you might prefer
+    * to keep references to those instances programmatically and calling `.scrapeData()` directly on them
+    * instead of using this function.
+    */
+  def latestScrapeData(): Option[String] =
+    _lastCreatedInstance.map(_.scrapeData())
+
+  class Factory extends ModuleFactory:
+    override def create(settings: ModuleFactory.Settings): Module =
+      val reporter = new PrometheusReporter(DefaultConfigPath, settings.config)
+      _lastCreatedInstance = Some(reporter)
+      reporter
+
+  def create(): PrometheusReporter =
+    new PrometheusReporter()
+
+  case class Settings(generic: PrometheusSettings.Generic)
+
+  def readSettings(prometheusConfig: Config): PrometheusReporter.Settings =
+    PrometheusReporter.Settings(
+      generic = PrometheusSettings.readSettings(prometheusConfig)
+    )