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OpenTelemetry Exemplars

The DefaultExemplarSampler will provide OpenTelemetry exemplars if the opentelemetry-java library version 0.16.0 or higher is found. When client_java 0.11.0 was released, the current opentelemetry-java version was 1.2.0.

Running the Example

If you want to see this in action, you can run the example from the ExemplarsClientJavaIT:

./mvnw package
cd integration_tests/exemplars_otel_agent/target/
curl -LO https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases/download/v1.2.0/opentelemetry-javaagent-all.jar
java -Dotel.traces.exporter=logging -Dotel.metrics.exporter=none -javaagent:./opentelemetry-javaagent-all.jar -jar ./sample-rest-application.jar

Now you have a Spring REST service running on http://localhost:8080/hello that is instrumented with the OpenTelemetry Java agent.

Run a request to generate an OpenTelemetry trace

curl http://localhost:8080/hello

In order to get metrics in OpenMetrics format, run

curl -H 'Accept: application/openmetrics-text; version=1.0.0; charset=utf-8' http://localhost:8080/metrics

You should see metrics with Exemplars, for example in the request_duration_histogram metric:

request_duration_histogram_bucket{path="/god-of-fire",le="0.004"} 4.0 # {trace_id="043cd631811e373e4180a678c06b128e",span_id="cd122e457d2ca5b0"} 0.0033 1618261159.027

Note that this is an example application for demonstration, so durations don't represent real durations, and some example metrics might not make sense in the real world.

Disabling OpenTelemetry Exemplars

If you use OpenTelemetry tracing but do not want Exemplars, you can disable OpenTelemetries in multiple ways.

Disabling OpenTelemetry Exemplars in Code

The default exemplar sampler can be disabled via the ExemplarConfig API. This is described in [README.md], as this is not specific to OpenTelemetry.

Disabling OpenTelemetry Exemplars at Compile Time

If you don't want to change code, but still build an application that uses OpenTelemetry but does not provide OpenTelemetry exemplars, you can exclude the corresponding dependencies in your pom.xml:

<dependencies>
  <dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>simpleclient</artifactId>
    <version>0.11.0</version>
    <exclusions>
      <!-- The following will disable OpenTelemetry exemplars when your application uses OpenTelemetry directly -->
      <exclusion>
        <groupId>io.prometheus</groupId>
        <artifactId>simpleclient_tracer_otel</artifactId>
      </exclusion>
      <!-- The following will disable OpenTelemetry exemplars when your application uses the OpenTelemetry Java agent -->
      <exclusion>
        <groupId>io.prometheus</groupId>
        <artifactId>simpleclient_tracer_otel_agent</artifactId>
      </exclusion>
    </exclusions>
  </dependency>
</dependencies>

Disable OpenTelemetry Exemplars at Runtime

If your application uses OpenTelemetry tracing, but you want to disable OpenTelemetry at runtime without changing code, start your application with the io.prometheus.otelExemplars system property:

java -Dio.prometheus.otelExemplars=inactive -jar my-application.jar