How to access metrics of Alpakka CommittableSource with back off? - akka

Question

Accessing the metrics of an Alpakka PlainSource seems fairly straight forward, but how can I do the same thing with a CommittableSource?
I currently have a simple consumer, something like this:
class Consumer(implicit val ma: ActorMaterializer, implicit val ec: ExecutionContext) extends Actor {
private val settings = ConsumerSettings(
context.system,
new ByteArrayDeserializer,
new StringDeserializer)
.withProperties(...)
override def receive: Receive = Actor.emptyBehavior
RestartSource
.withBackoff(minBackoff = 2.seconds, maxBackoff = 20.seconds, randomFactor = 0.2)(consumer)
.runForeach { handleMessage }
private def consumer() = {
AkkaConsumer
.committableSource(settings, Subscriptions.topics(Set(topic)))
.log(getClass.getSimpleName)
.withAttributes(ActorAttributes.supervisionStrategy(_ => Supervision.Resume))
}
private def handleMessage(message: CommittableMessage[Array[Byte], String]): Unit = {
...
}
}
How can I get access to the consumer metrics in this case?

Answer 1

We are using the Java prometheus client and I solved my issue with a custom collector that fetches its metrics directly from JMX:
import java.lang.management.ManagementFactory
import java.util
import io.prometheus.client.Collector
import io.prometheus.client.Collector.MetricFamilySamples
import io.prometheus.client.CounterMetricFamily
import io.prometheus.client.GaugeMetricFamily
import javax.management.ObjectName
import scala.collection.JavaConverters._
import scala.collection.mutable
class ConsumerMetricsCollector(val labels: Map[String, String] = Map.empty) extends Collector {
val metrics: mutable.Map[String, MetricFamilySamples] = mutable.Map.empty
def collect: util.List[MetricFamilySamples] = {
val server = ManagementFactory.getPlatformMBeanServer
for {
attrType <- List("consumer-metrics", "consumer-coordinator-metrics", "consumer-fetch-manager-metrics")
name <- server.queryNames(new ObjectName(s"kafka.consumer:type=$attrType,client-id=*"), null).asScala
attrInfo <- server.getMBeanInfo(name).getAttributes.filter { _.getType == "double" }
} yield {
val attrName = attrInfo.getName
val metricLabels = attrName.split(",").map(_.split("=").toList).collect {
case "client-id" :: (id: String) :: Nil => ("client-id", id)
}.toList ++ labels
val metricName = "kafka_consumer_" + attrName.replaceAll(raw"""[^\p{Alnum}]+""", "_")
val labelKeys = metricLabels.map(_._1).asJava
val metric = metrics.getOrElseUpdate(metricName,
if(metricName.endsWith("_total") || metricName.endsWith("_sum")) {
new CounterMetricFamily(metricName, attrInfo.getDescription, labelKeys)
} else {
new GaugeMetricFamily(metricName, attrInfo.getDescription, labelKeys)
}: MetricFamilySamples
)
val metricValue = server.getAttribute(name, attrName).asInstanceOf[Double]
val labelValues = metricLabels.map(_._2).asJava
metric match {
case f: CounterMetricFamily => f.addMetric(labelValues, metricValue)
case f: GaugeMetricFamily => f.addMetric(labelValues, metricValue)
case _ =>
}
}
metrics.values.toList.asJava
}
}