Add global labels to the OpenTelemetry metrics implementation [PLEN-5] (#15407)

ledger/metrics/BUILD.bazel

@@ -24,6 +24,7 @@ da_scala_library(
     runtime_deps = [],
     deps = [
         "//ledger/ledger-resources",
+        "//libs-scala/build-info",
         "//libs-scala/concurrent",
         "//libs-scala/resources",
         "//libs-scala/resources-akka",

ledger/metrics/src/main/scala/com/daml/metrics/api/MetricsContext.scala

@@ -15,6 +15,8 @@ case class MetricsContext(labels: Map[String, String]) {
       .build()
   }
 
+  def merge(context: MetricsContext): MetricsContext = this.copy(labels = labels ++ context.labels)
+
 }
 
 object MetricsContext {

ledger/metrics/src/main/scala/com/daml/metrics/api/opentelemetry/OpenTelemetryFactory.scala

@@ -6,6 +6,7 @@ package com.daml.metrics.api.opentelemetry
 import java.time.Duration
 import java.util.concurrent.TimeUnit
 
+import com.daml.buildinfo.BuildInfo
 import com.daml.metrics.api.Gauges.VarGauge
 import com.daml.metrics.api.MetricHandle.Timer.TimerHandle
 import com.daml.metrics.api.MetricHandle.{Counter, Factory, Gauge, Histogram, Meter, Timer}
@@ -20,7 +21,12 @@ import io.opentelemetry.api.metrics.{
 
 trait OpenTelemetryFactory extends Factory {
 
+  val globalMetricsContext: MetricsContext = MetricsContext(
+    Map("daml_version" -> BuildInfo.Version)
+  )
+
   def otelMeter: OtelMeter
+
   override def timer(
       name: MetricName
   )(implicit
@@ -29,12 +35,12 @@ trait OpenTelemetryFactory extends Factory {
     OpentelemetryTimer(
       name,
       otelMeter.histogramBuilder(name).ofLongs().setUnit("ms").build(),
-      context,
+      globalMetricsContext.merge(context),
     )
   override def gauge[T](name: MetricName, initial: T)(implicit
       context: MetricsContext = MetricsContext.Empty
   ): MetricHandle.Gauge[T] = {
-    val attributes = context.asAttributes
+    val attributes = globalMetricsContext.merge(context).asAttributes
     initial match {
       case longInitial: Int =>
         val varGauge = new VarGauge[Int](longInitial)
@@ -67,7 +73,7 @@ trait OpenTelemetryFactory extends Factory {
       context: MetricsContext = MetricsContext.Empty
   ): Unit = {
     val value = valueSupplier()
-    val attributes = context.asAttributes
+    val attributes = globalMetricsContext.merge(context).asAttributes
     value match {
       case _: Int =>
         otelMeter
@@ -104,21 +110,21 @@ trait OpenTelemetryFactory extends Factory {
   ): Meter = OpentelemetryMeter(
     name,
     otelMeter.counterBuilder(name).build(),
-    context,
+    globalMetricsContext.merge(context),
   )
   override def counter(name: MetricName)(implicit
       context: MetricsContext = MetricsContext.Empty
   ): MetricHandle.Counter = OpentelemetryCounter(
     name,
     otelMeter.upDownCounterBuilder(name).build(),
-    context,
+    globalMetricsContext.merge(context),
   )
   override def histogram(name: MetricName)(implicit
       context: MetricsContext = MetricsContext.Empty
   ): MetricHandle.Histogram = OpentelemetryHistogram(
     name,
     otelMeter.histogramBuilder(name).ofLongs().build(),
-    context,
+    globalMetricsContext.merge(context),
   )
 }
 

ledger/metrics/src/test/suite/scala/com/daml/metrics/api/MetricsContextSpec.scala

@@ -0,0 +1,47 @@
+// Copyright (c) 2022 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package com.daml.metrics.api
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+class MetricsContextSpec extends AnyWordSpec with Matchers {
+
+  "merging metrics contexts" should {
+
+    "merge all labels" in {
+      MetricsContext(
+        Map("key" -> "value")
+      ).merge(
+        MetricsContext(
+          Map("key2" -> "value")
+        )
+      ) should equal(
+        MetricsContext(
+          Map(
+            "key" -> "value",
+            "key2" -> "value",
+          )
+        )
+      )
+    }
+
+    "handle duplicate labels" in {
+      MetricsContext(
+        Map("key" -> "value1")
+      ).merge(
+        MetricsContext(
+          Map("key" -> "value2")
+        )
+      ) should equal(
+        MetricsContext(
+          Map(
+            "key" -> "value2"
+          )
+        )
+      )
+    }
+  }
+
+}