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Welcome to reactive-streams-telemetry!

The goal of this Scala library is to provide an Reactive Streams interface to an application instance's working set of metrics and traces, thereby providing control over resource usage.

Metrics and traces are presented using streams where elements pertain to a metric and span respectively. Applications can then consume these streams and present them however they wish e.g. Akka HTTP can be used to serve a snapshot of metrics and traces as JSON with an HTTP GET route. Another example could be where metrics and traces are published over UDP to your favorite collection engine.

Akka Streams is used as the Reactive Streams interface and implementation with reporting for Drop Wizard Metrics and Open Tracing via Jaeger Tracing. We also provide a JSON encoding as a convenience and use spray-json for this purpose.

Other than the libraries declared above, there are no additional dependencies.


Serve up the latest telemetry gathered given an Alpakka Unix Domain Socket and the establishment of the metrics and traces sources (described following this):

val source =
    .map { snapshot =>
      import MetricsJsonProtocol._
      JsObject("metricsSnapshot" -> snapshot.toJson).compactPrint
        .map { span =>
          import TracingJsonProtocol._
          JsObject("span" -> span.toJson).compactPrint
    .map(s => ByteString(s + "\n")) // Having a newline delim helps consumers such as 'jq' to parse it

  .bindAndHandle(Flow.fromSinkAndSourceCoupled(Sink.ignore, source),
                 new File("/var/run/mysocket.sock"))

Then, using nc and jq, you can connect to your app and stream out prettified JSON:

$ nc -v -U /var/run/mysocket.sock | jq
  "metricsSnapshot": {
    "counters": {
      "lora-server.messages-appended": 0,
      "lora-server.downlink-packets-rx": 14,
      "lora-server.unsupported-payload": 0,
      "lora-server.uplink-packets-tx": 7
    "gauges": {},
    "histograms": {},
    "meters": {
      "lora-server.valid-data-up": {
        "fifteenMinuteRate": 0,
        "count": 0,
        "fiveMinuteRate": 0,
        "oneMinuteRate": 0,
        "meanRate": 0
    "timers": {}
  "span": {
    "baggage": [],
    "duration": 1667,
    "logs": [],
    "operationName": "uplink-rx-to-ack",
    "references": [],
    "spanId": -5323514506617469000,
    "start": 1551332653982000,
    "tags": {
      "sampler.type": "const",
      "sampler.param": "true"
    "traceId": -5323514506617469000


Builds are published to Maven Central. Please substitute version accordingly.

"" %% "reactive-streams-telemetry" % version

Metrics setup

import com.codahale.metrics._
import java.util.concurrent.TimeUnit

val metricRegistry = new MetricRegistry()

val reporter = new MetricsReporter(

Tracing setup

import io.jaegertracing.internal.{ JaegerTracer => Tracer }

val reporter = new TracingReporter(1)

val tracer = new Tracer.Builder("my-tracing-service")

JSON serialization

To use the JSON serialization you import MetricsJsonProtocol or TracingJsonProtocol for metrics and tracing respectively. Here's an example of how to serialize Span objects to JSON:

import{TracingJsonProtocol, TracingReporter}
import io.jaegertracing.internal.{ JaegerTracer => Tracer }
import io.jaegertracing.internal.samplers.ConstSampler

val reporter = new TracingReporter(1)

val sampler = new ConstSampler(true)

val tracer = new Tracer.Builder("tracing-reporter-tests")

val span = tracer.buildSpan("some-span").start()
span.log(0, "hello-world")

import TracingJsonProtocol._

  .map (_.toJson)

Contribution policy

Contributions via GitHub pull requests are gladly accepted from their original author. Along with any pull requests, please state that the contribution is your original work and that you license the work to the project under the project's open source license. Whether or not you state this explicitly, by submitting any copyrighted material via pull request, email, or other means you agree to license the material under the project's open source license and warrant that you have the legal authority to do so.


You'll need a GPG key to sign as artifacts are published to Sonatype for publishing at Maven Central. Once you have GPG setup:

export GPG_TTY=$(tty)
sbt publishSigned


This code is open source software licensed under the Apache-2.0 license.

(c) Copyright Titan Class Pty Ltd, 2019