Kamon http4s

Getting Started

The kamon-http4s module brings traces and metrics to your http4s based applications.

Kamon kamon-http4s is currently available for Scala 2.11 and 2.12.

Supported releases and dependencies are shown below.

kamon-http4s	status	jdk	scala	http4s
1.0.8-1.0.10	stable	1.8+	2.11, 2.12	0.18.x
1.0.13	stable	1.8+	2.11, 2.12	0.20.x

To get started with SBT, simply add the following to your build.sbt file:

libraryDependencies += "io.kamon" %% "kamon-http4s" % "1.0.13"

Metrics and Tracing for http4s in 2 steps

The Server

def serve[F[_]](implicit Effect: Effect[F], EC: ExecutionContext) : Stream[F, StreamApp.ExitCode] =
    for {
      _ <- Stream.eval(Sync[F].delay(println("Starting Google Service with Client")))
      client <- Http1Client.stream[F]()
      service = GoogleService.service[F](middleware.client.KamonSupport(client)) (1)
      exitCode <- BlazeBuilder[F]
        .bindHttp(Config.server.port, Config.server.interface)
        .mountService(middleware.server.KamonSupport(service)) (2)
        .serve
    } yield exitCode

(1): The Kamon Middleware for the Client side.
(2): The Kamon Middleware for the Server side.

The Service

object GoogleService {
  def service[F[_]: Effect](c: Client[F]): HttpService[F] = {
    val dsl = new Http4sDsl[F]{}
    import dsl._

    HttpService[F] {
      case GET -> Root / "call-google" =>
        Ok(c.expect[String]("https://www.google.com.ar"))
    }
  }
}

Step 1: Add the Kamon Libraries

libraryDependencies ++= Seq(
  "io.kamon" %% "kamon-core" % "1.1.2",
  "io.kamon" %% "kamon-system-metrics" % "1.0.1",
  "io.kamon" %% "kamon-prometheus" % "1.0.0",
  "io.kamon" %% "kamon-http4s" % "1.0.7",
  "io.kamon" %% "kamon-zipkin" % "1.0.1",
  "io.kamon" %% "kamon-jaeger" % "1.0.2"
)

Step 2: Start Reporting your Data

The last step in the process: start reporting your data! You can register as many reporters as you want by using the Kamon.addReporter(...) function:

Kamon.addReporter(new PrometheusReporter())
Kamon.addReporter(new ZipkinReporter())
Kamon.addReporter(new Jaeger())

Now you can simply sbt run the application and after a few seconds you will get the Prometheus metrics exposed on http://localhost:9095/ and message traces sent to Zipkin! The default configuration publishes the Prometheus endpoint on port 9095 and assumes that you have a Zipkin instance running locally on port 9411 but you can change these values under the kamon.prometheus and kamon.zipkin configuration keys, respectively.

Metrics

All you need to do is configure a scrape configuration in Prometheus. The following snippet is a minimal example that should work with the minimal server from the previous section.

A minimal Prometheus configuration snippet
------------------------------------------------------------------------------
scrape_configs:
  - job_name: 'kamon-prometheus'
    static_configs:
      - targets: ['localhost:9095']
------------------------------------------------------------------------------

Once you configure this target in Prometheus you are ready to run some queries like this:

Those are the Server Metrics metrics that we are gathering by default:

active-requests: The the number active requests.
http-responses: Response time by status code.
abnormal-termination: The number of abnormal requests termination.
service-errors: The number of service errors.
headers-times: The number of abnormal requests termination.
http-request: Request time by status code.

Now you can go ahead, make your custom metrics and create your own dashboards!

Traces

Assuming that you have a Zipkin instance running locally with the default ports, you can go to http://localhost:9411 and start investigating traces for this application. Once you find a trace you are interested in you will see something like this:

Clicking on a span will bring up a details view where you can see all tags for the selected span:

Enjoy!

That's it, you are now collecting metrics and tracing information from a http4s application.

Useful links:

Example of how to correctly configure the execution context by @cmcmteixeira

kurlov/kamon-http4s