Earthquake API

Example Ktor application instrumented with OpenTracing using ktor-opentracing.

Retrieves data about earthquakes that happened today using an API from the U.S. Geological Survey.

Running

1. Start an all-in-one Jaeger backend with in-memory storage.

    docker run -d --name jaeger \
      -e COLLECTOR_ZIPKIN_HTTP_PORT=9411 \
      -p 5775:5775/udp \
      -p 6831:6831/udp \
      -p 6832:6832/udp \
      -p 5778:5778 \
      -p 16686:16686 \
      -p 14268:14268 \
      -p 14250:14250 \
      -p 9411:9411 \
      jaegertracing/all-in-one:1.20
   

2. Start the application.

    ./gradlew run
   

3. Send some requests. Other routes available are /earthquake/biggest and /earthquake/biggerthan/5 (where 5 is a parameter).

    curl localhost:8080/earthquake/latest
    {
      "location" : "21 km SSE of Karluk, Alaska",
      "magnitude" : 1.9,
      "timeGMT" : "2020-11-02 09:46:39"
    }  
   

4. See traces in Jaeger.

   http://localhost:16686/

5. Stop the Jaeger docker container.

    docker ps
    docker stop <containerId>
   

Steps

1. Import ktor-opentracing and the Java Jaeger client (commit).

    implementation "io.jaegertracing:jaeger-client:1.3.2"
    implementation "com.zopa:ktor-opentracing:0.3.5"
   

2. Instantiate a tracer and register it in GlobalTracer (commit).

    val tracer = Configuration("tracing-example")
        .withSampler(Configuration.SamplerConfiguration.fromEnv()
            .withType(ConstSampler.TYPE)
            .withParam(1))
        .withReporter(Configuration.ReporterConfiguration.fromEnv()
            .withLogSpans(true)
            .withSender(
                Configuration.SenderConfiguration()
                    .withAgentHost("localhost")
                    .withAgentPort(6831))).tracerBuilder
        .withScopeManager(ThreadContextElementScopeManager())
        .build()
    
    GlobalTracer.registerIfAbsent(tracer)
   

3. Install the OpenTracingServer feature into the application call pipeline (commit).

    install(OpenTracingServer)
   

4. Install the OpenTracingClient feature onto the http client (commit).

    install(OpenTracingClient)
   

5. Instrument method calls using the span helper function (commit).

    = span("EarthquakeClient.getBiggest()") {
   

   From the lamdba expression passed to span, you can add tags or logs to the span by calling setTag() or log().