Instrumentation

Manual instrumentation for OpenTelemetry Java

Instrumentation is the act of adding observability code to an app yourself.

If you’re instrumenting an app, you need to use the OpenTelemetry SDK for your language. You’ll then use the SDK to initialize OpenTelemetry and the API to instrument your code. This will emit telemetry from your app, and any library you installed that also comes with instrumentation.

If you’re instrumenting a library, only install the OpenTelemetry API package for your language. Your library will not emit telemetry on its own. It will only emit telemetry when it is part of an app that uses the OpenTelemetry SDK. For more on instrumenting libraries, see Libraries.

For more information about the OpenTelemetry API and SDK, see the specification.

Example app preparation

This page uses a modified version of the example app from Getting Started to help you learn about manual instrumentation.

You don’t have to use the example app: if you want to instrument your own app or library, follow the instructions here to adapt the process to your own code.

Dependencies

To begin, set up an environment in a new directory called java-simple. Within that directory, create a file called build.gradle.kts with the following content:

plugins {
  id("java")
  id("org.springframework.boot") version "3.0.6"
  id("io.spring.dependency-management") version "1.1.0"
}

sourceSets {
  main {
    java.setSrcDirs(setOf("."))
  }
}

repositories {
  mavenCentral()
}

dependencies {
  implementation("org.springframework.boot:spring-boot-starter-web")
}

Create and launch an HTTP Server

To highlight the difference between instrumenting a library and a standalone app, split out the dice rolling into a library class, which then will be imported as a dependency by the app.

Create the library file name Dice.java and add the following code to it:

package otel;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;

public class Dice {

  private int min;
  private int max;

  public Dice(int min, int max) {
    this.min = min;
    this.max = max;
  }

  public List<Integer> rollTheDice(int rolls) {
    List<Integer> results = new ArrayList<Integer>();
    for (int i = 0; i < rolls; i++) {
      results.add(this.rollOnce());
    }
    return results;
  }

  private int rollOnce() {
    return ThreadLocalRandom.current().nextInt(this.min, this.max + 1);
  }
}

Create the app files DiceApplication.java and RollController.java and add the following code to them:

// DiceApplication.java
package otel;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.Banner;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DiceApplication {
  public static void main(String[] args) {

    SpringApplication app = new SpringApplication(DiceApplication.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(args);
  }
}
// RollController.java
package otel;

import java.util.List;
import java.util.Optional;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.server.ResponseStatusException;

import otel.Dice;

@RestController
public class RollController {
  private static final Logger logger = LoggerFactory.getLogger(RollController.class);

  @GetMapping("/rolldice")
  public List<Integer> index(@RequestParam("player") Optional<String> player,
      @RequestParam("rolls") Optional<Integer> rolls) {

    if (!rolls.isPresent()) {
      throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Missing rolls parameter", null);
    }

    List<Integer> result = new Dice(1, 6).rollTheDice(rolls.get());

    if (player.isPresent()) {
      logger.info("{} is rolling the dice: {}", player.get(), result);
    } else {
      logger.info("Anonymous player is rolling the dice: {}", result);
    }
    return result;
  }
}

To ensure that it is working, run the application with the following command and open http://localhost:8080/rolldice?rolls=12 in your web browser:

gradle assemble
java -jar ./build/libs/java-simple.jar

You should get a list of 12 numbers in your browser window, for example:

[5,6,5,3,6,1,2,5,4,4,2,4]

Manual instrumentation setup

For both library and app instrumentation, the first step is to install the dependencies for the OpenTelemetry API.

Throughout this documentation you will add dependencies. For a full list of artifact coordinates, see releases. For semantic convention releases, see semantic-conventions-java.

Dependency management

A Bill of Material (BOM) ensures that versions of dependencies (including transitive ones) are aligned. Importing the opentelemetry-bom BOM is important to ensure version alignment across all OpenTelemetry dependencies.

dependencyManagement {
  imports {
    mavenBom("io.opentelemetry:opentelemetry-bom:1.35.0")
  }
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web");
    implementation("io.opentelemetry:opentelemetry-api");
}

If you are not using Spring and its io.spring.dependency-management dependency management plugin, install the OpenTelemetry BOM and API using Gradle dependencies only.

dependencies {
    implementation(platform("io.opentelemetry:opentelemetry-bom:1.35.0"));
    implementation("io.opentelemetry:opentelemetry-api");
}
<project>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>io.opentelemetry</groupId>
                <artifactId>opentelemetry-bom</artifactId>
                <version>1.35.0</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-api</artifactId>
        </dependency>
    </dependencies>
</project>

Initialize the SDK

The OpenTelemetry API provides a set of interfaces for collecting telemetry, but the data is dropped without an implementation. The OpenTelemetry SDK is the implementation of the OpenTelemetry API provided by OpenTelemetry. To use it if you instrument a Java app, begin by installing dependencies:

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web");
    implementation("io.opentelemetry:opentelemetry-api");
    implementation("io.opentelemetry:opentelemetry-sdk");
    implementation("io.opentelemetry:opentelemetry-exporter-logging");
    implementation("io.opentelemetry.semconv:opentelemetry-semconv:1.23.1-alpha");
}
<project>
    <dependencies>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-sdk</artifactId>
        </dependency>
        <dependency>
            <groupId>io.opentelemetry</groupId>
            <artifactId>opentelemetry-exporter-logging</artifactId>
        </dependency>
        <dependency>
            <!-- Not managed by opentelemetry-bom -->
            <groupId>io.opentelemetry.semconv</groupId>
            <artifactId>opentelemetry-semconv</artifactId>
            <version>1.23.1-alpha</version>
        </dependency>
    </dependencies>
</project>

If you are an application developer, you need to configure an instance of the OpenTelemetrySdk as early as possible in your application. This can either be done manually by using the OpenTelemetrySdk.builder() or by using the SDK autoconfiguration extension through the opentelemetry-sdk-extension-autoconfigure module. It is recommended to use autoconfiguration, as it is easier to use and comes with various additional capabilities.

Automatic Configuration

To use autoconfiguration add the following dependency to your application:

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web");
    implementation("io.opentelemetry:opentelemetry-api");
    implementation("io.opentelemetry:opentelemetry-sdk");
    implementation("io.opentelemetry:opentelemetry-exporter-logging");
    implementation("io.opentelemetry.semconv:opentelemetry-semconv:1.23.1-alpha");
    implementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure");
}
<project>
    <dependencies>
        <dependency>
          <groupId>io.opentelemetry</groupId>
          <artifactId>opentelemetry-sdk-extension-autoconfigure</artifactId>
        </dependency>
        <dependency>
          <groupId>io.opentelemetry</groupId>
          <artifactId>opentelemetry-sdk-extension-autoconfigure-spi</artifactId>
        </dependency>
    </dependencies>
</project>

It allows you to autoconfigure the OpenTelemetry SDK based on a standard set of supported environment variables and system properties. Each environment variable has a corresponding system property named the same way but as lower case and using the . (dot) character instead of the _ (underscore) as separator.

The logical service name can be specified via the OTEL_SERVICE_NAME environment variable (or otel.service.name system property).

The traces, metrics or logs exporters can be set via the OTEL_TRACES_EXPORTER, OTEL_METRICS_EXPORTER and OTEL_LOGS_EXPORTER environment variables. For example OTEL_TRACES_EXPORTER=logging configures your application to use an exporter that writes all traces to the console. The corresponding exporter library has to be provided in the classpath of the application as well.

For debugging and local development purposes, use the logging exporter. After you have finished setting up manual instrumentation, provide an appropriate exporter library in the classpath of the application to export the app’s telemetry data to one or more telemetry backends.

The SDK autoconfiguration has to be initialized as early as possible in the application lifecycle in order to allow the module to go through the provided environment variables (or system properties) and set up the OpenTelemetry instance by using the builders internally.

import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;

OpenTelemetrySdk sdk = AutoConfiguredOpenTelemetrySdk.initialize()
    .getOpenTelemetrySdk();

In the case of the example app the DiceApplication class gets updated as follows:

package otel;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.Banner;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;

@SpringBootApplication
public class DiceApplication {
  public static void main(String[] args) {
    SpringApplication app = new SpringApplication(DiceApplication.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(args);
  }

  @Bean
  public OpenTelemetry openTelemetry() {
    return AutoConfiguredOpenTelemetrySdk.initialize().getOpenTelemetrySdk();
  }
}

To verify your code, build and run the app:

gradle assemble
env \
OTEL_SERVICE_NAME=dice-server \
OTEL_TRACES_EXPORTER=logging \
OTEL_METRICS_EXPORTER=logging \
OTEL_LOGS_EXPORTER=logging \
OTEL_METRIC_EXPORT_INTERVAL=15000 \
java -jar ./build/libs/java-simple.jar

This basic setup has no effect on your app yet. You need to add code for traces, metrics, and/or logs.

Note that OTEL_METRIC_EXPORT_INTERVAL=15000 (milliseconds) is a temporary setting to test that your metrics are properly generated. Remember to remove the setting once you are done testing. The default is 60000 milliseconds.

Manual Configuration

OpenTelemetrySdk.builder() returns an instance of OpenTelemetrySdkBuilder, which gets the providers related to the signals, tracing and metrics, in order to build the OpenTelemetry instance.

You can build the providers by using the SdkTracerProvider.builder() and SdkMeterProvider.builder() methods.

In the case of the example app the the DiceApplication class gets updated as follows:

package otel;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.Banner;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.common.Attributes;
import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
import io.opentelemetry.context.propagation.ContextPropagators;
import io.opentelemetry.exporter.logging.LoggingMetricExporter;
import io.opentelemetry.exporter.logging.LoggingSpanExporter;
import io.opentelemetry.exporter.logging.SystemOutLogRecordExporter;
import io.opentelemetry.sdk.OpenTelemetrySdk;
import io.opentelemetry.sdk.metrics.SdkMeterProvider;
import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
import io.opentelemetry.sdk.resources.Resource;
import io.opentelemetry.sdk.trace.SdkTracerProvider;
import io.opentelemetry.sdk.trace.export.SimpleSpanProcessor;
import io.opentelemetry.sdk.logs.SdkLoggerProvider;
import io.opentelemetry.sdk.logs.export.BatchLogRecordProcessor;
import io.opentelemetry.sdk.logs.export.LogRecordExporter;
import io.opentelemetry.semconv.ResourceAttributes;

@SpringBootApplication
public class DiceApplication {
  public static void main(String[] args) {
    SpringApplication app = new SpringApplication(DiceApplication.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(args);
  }

  @Bean
  public OpenTelemetry openTelemetry() {
    Resource resource = Resource.getDefault().toBuilder().put(ResourceAttributes.SERVICE_NAME, "dice-server").put(ResourceAttributes.SERVICE_VERSION, "0.1.0").build();

    SdkTracerProvider sdkTracerProvider = SdkTracerProvider.builder()
        .addSpanProcessor(SimpleSpanProcessor.create(LoggingSpanExporter.create()))
        .setResource(resource)
        .build();

    SdkMeterProvider sdkMeterProvider = SdkMeterProvider.builder()
        .registerMetricReader(PeriodicMetricReader.builder(LoggingMetricExporter.create()).build())
        .setResource(resource)
        .build();

    SdkLoggerProvider sdkLoggerProvider = SdkLoggerProvider.builder()
        .addLogRecordProcessor(BatchLogRecordProcessor.builder(SystemOutLogRecordExporter.create()).build())
        .setResource(resource)
        .build();

    OpenTelemetry openTelemetry = OpenTelemetrySdk.builder()
        .setTracerProvider(sdkTracerProvider)
        .setMeterProvider(sdkMeterProvider)
        .setLoggerProvider(sdkLoggerProvider)
        .setPropagators(ContextPropagators.create(TextMapPropagator.composite(W3CTraceContextPropagator.getInstance(), W3CBaggagePropagator.getInstance())))
        .buildAndRegisterGlobal();

    return openTelemetry;
  }
}

For debugging and local development purposes, the example exports telemetry to the console. After you have finished setting up manual instrumentation, you need to configure an appropriate exporter to export the app’s telemetry data to one or more telemetry backends.

The example also sets up the mandatory SDK default attribute service.name, which holds the logical name of the service, and the optional (but highly encouraged!) attribute service.version, which holds the version of the service API or implementation.

Alternative methods exist for setting up resource attributes. For more information, see Resources.

To verify your code, build and run the app:

gradle assemble
java -jar ./build/libs/java-simple.jar

This basic setup has no effect on your app yet. You need to add code for traces, metrics, and/or logs.

Traces

Initialize Tracing

To enable tracing in your app, you’ll need to have an initialized TracerProvider that will let you create a Tracer:

import io.opentelemetry.sdk.trace.SdkTracerProvider;

SdkTracerProvider sdkTracerProvider = SdkTracerProvider.builder()
  .addSpanProcessor(spanProcessor)
  .setResource(resource)
  .build();

If a TracerProvider is not created, the OpenTelemetry APIs for tracing will use a no-op implementation and fail to generate data.

If you followed the instructions to initialize the SDK above, you have a TracerProvider setup for you already. You can continue with acquiring a tracer.

Acquiring a Tracer

To do Tracing you’ll need to acquire a Tracer.

Note: Methods of the OpenTelemetry SDK should never be called.

First, a Tracer must be acquired, which is responsible for creating spans and interacting with the Context. A tracer is acquired by using the OpenTelemetry API specifying the name and version of the library instrumenting the instrumented library or application to be monitored. More information is available in the specification chapter Obtaining a Tracer.

Anywhere in your application where you write manual tracing code should call getTracer to acquire a tracer. For example:

import io.opentelemetry.api.trace.Tracer;

Tracer tracer = openTelemetry.getTracer("instrumentation-scope-name", "instrumentation-scope-version");

The values of instrumentation-scope-name and instrumentation-scope-version should uniquely identify the Instrumentation Scope, such as the package, module or class name. This will help later help determining what the source of telemetry is. While the name is required, the version is still recommended despite being optional. Note, that all Tracers that are created by a single OpenTelemetry instance will interoperate, regardless of name.

It’s generally recommended to call getTracer in your app when you need it rather than exporting the tracer instance to the rest of your app. This helps avoid trickier application load issues when other required dependencies are involved.

In the case of the example app, there are two places where a tracer may be acquired with an appropriate Instrumentation Scope:

First, in the index method of the RollController as follows:

package otel;

// ...
import org.springframework.beans.factory.annotation.Autowired;
import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.trace.Tracer;

@RestController
public class RollController {
  private static final Logger logger = LoggerFactory.getLogger(RollController.class);
  private final Tracer tracer;

  @Autowired
  RollController(OpenTelemetry openTelemetry) {
    tracer = openTelemetry.getTracer(RollController.class.getName(), "0.1.0");
  }
  // ...
}

And second, in the library file Dice.java:

// ...
import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.trace.Tracer;

public class Dice {

  private int min;
  private int max;
  private Tracer tracer;

  public Dice(int min, int max, OpenTelemetry openTelemetry) {
    this.min = min;
    this.max = max;
    this.tracer = openTelemetry.getTracer(Dice.class.getName(), "0.1.0");
  }

  public Dice(int min, int max) {
    this(min, max, OpenTelemetry.noop())
  }

  // ...
}

As an aside, if you are writing library instrumentation, it is strongly recommended that you provide your users the ability to inject an instance of OpenTelemetry into your instrumentation code. If this is not possible for some reason, you can fall back to using an instance from the GlobalOpenTelemetry class:

import io.opentelemetry.api.GlobalOpenTelemetry;

Tracer tracer = GlobalOpenTelemetry.getTracer("instrumentation-scope-name", "instrumentation-scope-version");

Note that you can’t force end users to configure the global, so this is the most brittle option for library instrumentation.

Create Spans

Now that you have tracers initialized, you can create spans.

To create Spans, you only need to specify the name of the span. The start and end time of the span is automatically set by the OpenTelemetry SDK.

The code below illustrates how to create a span:

import io.opentelemetry.api.trace.Span;
import io.opentelemetry.context.Scope;

// ...
  @GetMapping("/rolldice")
  public List<Integer> index(@RequestParam("player") Optional<String> player,
      @RequestParam("rolls") Optional<Integer> rolls) {
    Span span = tracer.spanBuilder("rollTheDice").startSpan();

    // Make the span the current span
    try (Scope scope = span.makeCurrent()) {

      if (!rolls.isPresent()) {
        throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Missing rolls parameter", null);
      }

      List<Integer> result = new Dice(1, 6).rollTheDice(rolls.get());

      if (player.isPresent()) {
        logger.info("{} is rolling the dice: {}", player.get(), result);
      } else {
        logger.info("Anonymous player is rolling the dice: {}", result);
      }
      return result;
    } catch(Throwable t) {
      span.recordException(t);
      throw t;
    } finally {
      span.end();
    }
  }

It’s required to call end() to end the span when you want it to end.

If you followed the instructions using the example app up to this point, you can copy the code above into the index method of the RollController. You should now be able to see spans emitted from your app.

Start your app as follows, and then send it requests by visiting http://localhost:8080/rolldice with your browser or curl:

gradle assemble
env \
OTEL_SERVICE_NAME=dice-server \
OTEL_TRACES_EXPORTER=logging \
OTEL_METRICS_EXPORTER=logging \
OTEL_LOGS_EXPORTER=logging \
java -jar ./build/libs/java-simple.jar

After a while, you should see the spans printed in the console by the LoggingSpanExporter, something like this:

2023-08-02T17:22:22.658+02:00  INFO 2313 --- [nio-8080-exec-1] i.o.e.logging.LoggingSpanExporter        : 'rollTheDice' : 565232b11b9933fa6be8d6c4a1307fe2 6e1e011e2e8c020b INTERNAL [tracer: otel.RollController:0.1.0] {}

Create nested Spans

Most of the time, we want to correlate spans for nested operations. OpenTelemetry supports tracing within processes and across remote processes. For more details how to share context between remote processes, see Context Propagation.

For example in the Dice class method rollTheDice calling method rollOnce, the spans could be manually linked in the following way:

import io.opentelemetry.api.trace.Span;
import io.opentelemetry.context.Context;
// ...
  public List<Integer> rollTheDice(int rolls) {
    Span parentSpan = tracer.spanBuilder("parent").startSpan();
    List<Integer> results = new ArrayList<Integer>();
    try {
      for (int i = 0; i < rolls; i++) {
        results.add(this.rollOnce(parentSpan));
      }
      return results;
    } finally {
      parentSpan.end();
    }
  }

  private int rollOnce(Span parentSpan) {
    Span childSpan = tracer.spanBuilder("child")
        .setParent(Context.current().with(parentSpan))
        .startSpan();
    try {
      return ThreadLocalRandom.current().nextInt(this.min, this.max + 1);
    } finally {
      childSpan.end();
    }
  }

The OpenTelemetry API offers also an automated way to propagate the parent span on the current thread:

import io.opentelemetry.api.trace.Span;
import io.opentelemetry.context.Scope;
// ...
  public List<Integer> rollTheDice(int rolls) {
    Span parentSpan = tracer.spanBuilder("parent").startSpan();
    try (Scope scope = parentSpan.makeCurrent()) {
      List<Integer> results = new ArrayList<Integer>();
      for (int i = 0; i < rolls; i++) {
        results.add(this.rollOnce());
      }
      return results;
    } finally {
      parentSpan.end();
    }
  }

  private int rollOnce() {
    Span childSpan = tracer.spanBuilder("child")
    // NOTE: setParent(...) is not required;
    // `Span.current()` is automatically added as the parent
    .startSpan();
    try(Scope scope = childSpan.makeCurrent()) {
      return ThreadLocalRandom.current().nextInt(this.min, this.max + 1);
    } finally {
      childSpan.end();
    }
  }
}

To link spans from remote processes, it is sufficient to set the Remote Context as parent.

Span childRemoteParent = tracer.spanBuilder("Child").setParent(remoteContext).startSpan();

Get the current span

Sometimes it’s helpful to do something with the current/active span at a particular point in program execution.

Span span = Span.current()

And if you want the current span for a particular Context object:

Span span = Span.fromContext(context)

Span Attributes

In OpenTelemetry spans can be created freely and it’s up to the implementor to annotate them with attributes specific to the represented operation. Attributes provide additional context on a span about the specific operation it tracks, such as results or operation properties.

Span span = tracer.spanBuilder("/resource/path").setSpanKind(SpanKind.CLIENT).startSpan();
span.setAttribute("http.method", "GET");
span.setAttribute("http.url", url.toString());

Semantic Attributes

There are semantic conventions for spans representing operations in well-known protocols like HTTP or database calls. Semantic conventions for these spans are defined in the specification at Trace Semantic Conventions.

First add the semantic conventions as a dependency to your application:

dependencies {
  implementation("io.opentelemetry.semconv:opentelemetry-semconv:1.23.1-alpha")
}
<dependency>
    <groupId>io.opentelemetry.semconv</groupId>
    <artifactId>opentelemetry-semconv</artifactId>
    <version>1.23.1-alpha</version>
</dependency>

Finally, you can update your file to include semantic attributes:

Span span = tracer.spanBuilder("/resource/path").setSpanKind(SpanKind.CLIENT).startSpan();
span.setAttribute(SemanticAttributes.HTTP_METHOD, "GET");
span.setAttribute(SemanticAttributes.HTTP_URL, url.toString());

Create Spans with events

Spans can be annotated with named events (called Span Events) that can carry zero or more Span Attributes, each of which itself is a key:value map paired automatically with a timestamp.

span.addEvent("Init");
...
span.addEvent("End");
Attributes eventAttributes = Attributes.of(
    AttributeKey.stringKey("key"), "value",
    AttributeKey.longKey("result"), 0L);

span.addEvent("End Computation", eventAttributes);

A Span may be linked to zero or more other Spans that are causally related via a Span Link. Links can be used to represent batched operations where a Span was initiated by multiple initiating Spans, each representing a single incoming item being processed in the batch.

Span child = tracer.spanBuilder("childWithLink")
        .addLink(parentSpan1.getSpanContext())
        .addLink(parentSpan2.getSpanContext())
        .addLink(parentSpan3.getSpanContext())
        .addLink(remoteSpanContext)
    .startSpan();

For more details how to read context from remote processes, see Context Propagation.

Set span status

A status can be set on a span, typically used to specify that a span has not completed successfully - SpanStatus.Error. In rare scenarios, you could override the Error status with OK, but don’t set OK on successfully-completed spans.

The status can be set at any time before the span is finished:

Span span = tracer.spanBuilder("my span").startSpan();
// put the span into the current Context
try (Scope scope = span.makeCurrent()) {
	// do something
} catch (Throwable t) {
  span.setStatus(StatusCode.ERROR, "Something bad happened!");
  throw t;
} finally {
  span.end(); // Cannot set a span after this call
}

Record exceptions in spans

It can be a good idea to record exceptions when they happen. It’s recommended to do this in conjunction with setting span status.

Span span = tracer.spanBuilder("my span").startSpan();
// put the span into the current Context
try (Scope scope = span.makeCurrent()) {
	// do something
} catch (Throwable throwable) {
  span.setStatus(StatusCode.ERROR, "Something bad happened!");
  span.recordException(throwable);
} finally {
  span.end(); // Cannot set a span after this call
}

This will capture things like the current stack trace in the span.

Context Propagation

OpenTelemetry provides a text-based approach to propagate context to remote services using the W3C Trace Context HTTP headers.

The following presents an example of an outgoing HTTP request using HttpURLConnection.

// Tell OpenTelemetry to inject the context in the HTTP headers
TextMapSetter<HttpURLConnection> setter =
  new TextMapSetter<HttpURLConnection>() {
    @Override
    public void set(HttpURLConnection carrier, String key, String value) {
        // Insert the context as Header
        carrier.setRequestProperty(key, value);
    }
};

URL url = new URL("http://127.0.0.1:8080/resource");
Span outGoing = tracer.spanBuilder("/resource").setSpanKind(SpanKind.CLIENT).startSpan();
try (Scope scope = outGoing.makeCurrent()) {
  // Use the Semantic Conventions.
  // (Note that to set these, Span does not *need* to be the current instance in Context or Scope.)
  outGoing.setAttribute(SemanticAttributes.HTTP_METHOD, "GET");
  outGoing.setAttribute(SemanticAttributes.HTTP_URL, url.toString());
  HttpURLConnection transportLayer = (HttpURLConnection) url.openConnection();
  // Inject the request with the *current*  Context, which contains our current Span.
  openTelemetry.getPropagators().getTextMapPropagator().inject(Context.current(), transportLayer, setter);
  // Make outgoing call
} finally {
  outGoing.end();
}
...

Similarly, the text-based approach can be used to read the W3C Trace Context from incoming requests. The following presents an example of processing an incoming HTTP request using HttpExchange.

TextMapGetter<HttpExchange> getter =
  new TextMapGetter<>() {
    @Override
    public String get(HttpExchange carrier, String key) {
      if (carrier.getRequestHeaders().containsKey(key)) {
        return carrier.getRequestHeaders().get(key).get(0);
      }
      return null;
    }

   @Override
   public Iterable<String> keys(HttpExchange carrier) {
     return carrier.getRequestHeaders().keySet();
   }
};
...
public void handle(HttpExchange httpExchange) {
  // Extract the SpanContext and other elements from the request.
  Context extractedContext = openTelemetry.getPropagators().getTextMapPropagator()
        .extract(Context.current(), httpExchange, getter);
  try (Scope scope = extractedContext.makeCurrent()) {
    // Automatically use the extracted SpanContext as parent.
    Span serverSpan = tracer.spanBuilder("GET /resource")
        .setSpanKind(SpanKind.SERVER)
        .startSpan();
    try {
      // Add the attributes defined in the Semantic Conventions
      serverSpan.setAttribute(SemanticAttributes.HTTP_METHOD, "GET");
      serverSpan.setAttribute(SemanticAttributes.HTTP_SCHEME, "http");
      serverSpan.setAttribute(SemanticAttributes.HTTP_HOST, "localhost:8080");
      serverSpan.setAttribute(SemanticAttributes.HTTP_TARGET, "/resource");
      // Serve the request
      ...
    } finally {
      serverSpan.end();
    }
  }
}

The following code presents an example to read the W3C Trace Context from incoming request, add spans, and further propagate the context. The example utilizes HttpHeaders to fetch the traceparent header for context propagation.

TextMapGetter<HttpHeaders> getter =
  new TextMapGetter<HttpHeaders>() {
    @Override
    public String get(HttpHeaders headers, String s) {
      assert headers != null;
      return headers.getHeaderString(s);
    }

    @Override
    public Iterable<String> keys(HttpHeaders headers) {
      List<String> keys = new ArrayList<>();
      MultivaluedMap<String, String> requestHeaders = headers.getRequestHeaders();
      requestHeaders.forEach((k, v) ->{
        keys.add(k);
      });
    }
};

TextMapSetter<HttpURLConnection> setter =
  new TextMapSetter<HttpURLConnection>() {
    @Override
    public void set(HttpURLConnection carrier, String key, String value) {
        // Insert the context as Header
        carrier.setRequestProperty(key, value);
    }
};

//...
public void handle(<Library Specific Annotation> HttpHeaders headers){
        Context extractedContext = opentelemetry.getPropagators().getTextMapPropagator()
                .extract(Context.current(), headers, getter);
        try (Scope scope = extractedContext.makeCurrent()) {
            // Automatically use the extracted SpanContext as parent.
            Span serverSpan = tracer.spanBuilder("GET /resource")
                .setSpanKind(SpanKind.SERVER)
                .startSpan();

            try(Scope ignored = serverSpan.makeCurrent()) {
                // Add the attributes defined in the Semantic Conventions
                serverSpan.setAttribute(SemanticAttributes.HTTP_METHOD, "GET");
                serverSpan.setAttribute(SemanticAttributes.HTTP_SCHEME, "http");
                serverSpan.setAttribute(SemanticAttributes.HTTP_HOST, "localhost:8080");
                serverSpan.setAttribute(SemanticAttributes.HTTP_TARGET, "/resource");

                HttpURLConnection transportLayer = (HttpURLConnection) url.openConnection();
                // Inject the request with the *current*  Context, which contains our current Span.
                openTelemetry.getPropagators().getTextMapPropagator().inject(Context.current(), transportLayer, setter);
                // Make outgoing call
            }finally {
                serverSpan.end();
            }
      }
}

Metrics

Spans provide detailed information about your application, but produce data that is proportional to the load on the system. In contrast, metrics combine individual measurements into aggregations, and produce data which is constant as a function of system load. The aggregations lack details required to diagnose low level issues, but complement spans by helping to identify trends and providing application runtime telemetry.

The metrics API defines a variety of instruments. Instruments record measurements, which are aggregated by the metrics SDK and eventually exported out of process. Instruments come in synchronous and asynchronous varieties. Synchronous instruments record measurements as they happen. Asynchronous instrument register a callback, which is invoked once per collection, and which records measurements at that point in time. The following instruments are available:

  • LongCounter/DoubleCounter: records only positive values, with synchronous and asynchronous options. Useful for counting things, such as the number of bytes sent over a network. Counter measurements are aggregated to always-increasing monotonic sums by default.
  • LongUpDownCounter/DoubleUpDownCounter: records positive and negative values, with synchronous and asynchronous options. Useful for counting things that go up and down, like the size of a queue. Up down counter measurements are aggregated to non-monotonic sums by default.
  • LongGauge/DoubleGauge: measures an instantaneous value with an asynchronous callback. Useful for recording values that can’t be merged across attributes, like CPU utilization percentage. Gauge measurements are aggregated as gauges by default.
  • LongHistogram/DoubleHistogram: records measurements that are most useful to analyze as a histogram distribution. No asynchronous option is available. Useful for recording things like the duration of time spent by an HTTP server processing a request. Histogram measurements are aggregated to explicit bucket histograms by default.

Note: The asynchronous varieties of counter and up down counter assume that the registered callback is observing the cumulative sum. For example, if you register an asynchronous counter whose callback records bytes sent over a network, it must record the cumulative sum of all bytes sent over the network, rather than trying to compute and record the difference since last call.

All metrics can be annotated with attributes: additional qualifiers that help describe what subdivision of the measurements the metric represents.

The following is an example of counter usage:

OpenTelemetry openTelemetry = // obtain instance of OpenTelemetry

// Gets or creates a named meter instance
Meter meter = openTelemetry.meterBuilder("instrumentation-library-name")
        .setInstrumentationVersion("1.0.0")
        .build();

// Build counter e.g. LongCounter
LongCounter counter = meter
      .counterBuilder("processed_jobs")
      .setDescription("Processed jobs")
      .setUnit("1")
      .build();

// It is recommended that the API user keep a reference to Attributes they will record against
Attributes attributes = Attributes.of(AttributeKey.stringKey("Key"), "SomeWork");

// Record data
counter.add(123, attributes);

The following is an example of usage of an asynchronous instrument:

// Build an asynchronous instrument, e.g. Gauge
meter
  .gaugeBuilder("cpu_usage")
  .setDescription("CPU Usage")
  .setUnit("ms")
  .buildWithCallback(measurement -> {
    measurement.record(getCpuUsage(), Attributes.of(AttributeKey.stringKey("Key"), "SomeWork"));
  });

Logs

Logs are distinct from metrics and traces in that there is no user-facing OpenTelemetry logs API. Instead, there is tooling to bridge logs from existing popular log frameworks (e.g. SLF4j, JUL, Logback, Log4j) into the OpenTelemetry ecosystem. For rationale behind this design decision, see Logging specification.

The two typical workflows discussed below each cater to different application requirements.

Direct to collector

In the direct to collector workflow, logs are emitted directly from an application to a collector using a network protocol (e.g. OTLP). This workflow is simple to set up as it doesn’t require any additional log forwarding components, and allows an application to easily emit structured logs that conform to the log data model. However, the overhead required for applications to queue and export logs to a network location may not be suitable for all applications.

To use this workflow:

  • Install appropriate Log Appender.
  • Configure the OpenTelemetry Log SDK to export log records to desired target destination (the collector or other).

Log appenders

A log appender bridges logs from a log framework into the OpenTelemetry Log SDK using the Logs Bridge API. Log appenders are available for various popular Java log frameworks:

The links above contain full usage and installation documentation, but installation is generally as follows:

  • Add required dependency via gradle or maven.
  • Extend the application’s log configuration (i.e. logback.xml, log4j.xml, etc) to include a reference to the OpenTelemetry log appender.
    • Optionally configure the log framework to determine which logs (i.e. filter by severity or logger name) are passed to the appender.
    • Optionally configure the appender to indicate how logs are mapped to OpenTelemetry Log Records (i.e. capture thread information, context data, markers, etc).

Log appenders automatically include the trace context in log records, enabling log correlation with traces.

The Log Appender example demonstrates setup for a variety of scenarios.

Via file or stdout

In the file or stdout workflow, logs are written to files or standout output. Another component (e.g. FluentBit) is responsible for reading / tailing the logs, parsing them to more structured format, and forwarding them a target, such as the collector. This workflow may be preferable in situations where application requirements do not permit additional overhead from direct to collector. However, it requires that all log fields required down stream are encoded into the logs, and that the component reading the logs parse the data into the log data model. The installation and configuration of log forwarding components is outside the scope of this document.

Log correlation with traces is available by installing log context instrumentation.

Log context instrumentation

OpenTelemetry provides components which enrich log context with trace context for various popular Java log frameworks:

This links above contain full usage and installation documentation, but installation is generally as follows:

  • Add required dependency via gradle or maven.
  • Extend the application’s log configuration (i.e. logback.xml or log4j.xml, etc) to reference the trace context fields in the log pattern.

SDK Configuration

The configuration examples reported in this document only apply to the SDK provided by opentelemetry-sdk. Other implementation of the API might provide different configuration mechanisms.

Tracing SDK

The application has to install a span processor with an exporter and may customize the behavior of the OpenTelemetry SDK.

For example, a basic configuration instantiates the SDK tracer provider and sets to export the traces to a logging stream.

SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
  .addSpanProcessor(BatchSpanProcessor.builder(LoggingSpanExporter.create()).build())
  .build();

Sampler

It is not always feasible to trace and export every user request in an application. In order to strike a balance between observability and expenses, traces can be sampled.

The OpenTelemetry SDK offers four samplers out of the box:

  • AlwaysOnSampler which samples every trace regardless of upstream sampling decisions.
  • AlwaysOffSampler which doesn’t sample any trace, regardless of upstream sampling decisions.
  • ParentBased which uses the parent span to make sampling decisions, if present.
  • TraceIdRatioBased which samples a configurable percentage of traces, and additionally samples any trace that was sampled upstream.

Additional samplers can be provided by implementing the io.opentelemetry.sdk.trace.Sampler interface.

SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
  .setSampler(Sampler.alwaysOn())
  //or
  .setSampler(Sampler.alwaysOff())
  //or
  .setSampler(Sampler.traceIdRatioBased(0.5))
  .build();

Span Processor

Different Span processors are offered by OpenTelemetry. The SimpleSpanProcessor immediately forwards ended spans to the exporter, while the BatchSpanProcessor batches them and sends them in bulk. Multiple Span processors can be configured to be active at the same time using the MultiSpanProcessor.

SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
  .addSpanProcessor(SimpleSpanProcessor.create(LoggingSpanExporter.create()))
  .addSpanProcessor(BatchSpanProcessor.builder(LoggingSpanExporter.create()).build())
  .build();

Exporter

Span processors are initialized with an exporter which is responsible for sending the telemetry data a particular backend. OpenTelemetry offers five exporters out of the box:

  • InMemorySpanExporter: keeps the data in memory, useful for testing and debugging.
  • Jaeger Exporter: prepares and sends the collected telemetry data to a Jaeger backend via gRPC. Varieties include JaegerGrpcSpanExporter and JaegerThriftSpanExporter.
  • ZipkinSpanExporter: prepares and sends the collected telemetry data to a Zipkin backend via the Zipkin APIs.
  • Logging Exporter: saves the telemetry data into log streams. Varieties include LoggingSpanExporter and OtlpJsonLoggingSpanExporter.
  • OpenTelemetry Protocol Exporter: sends the data in OTLP to the OpenTelemetry Collector or other OTLP receivers. Varieties include OtlpGrpcSpanExporter and OtlpHttpSpanExporter.

Other exporters can be found in the OpenTelemetry Registry.

ManagedChannel jaegerChannel = ManagedChannelBuilder.forAddress("localhost", 3336)
  .usePlaintext()
  .build();

JaegerGrpcSpanExporter jaegerExporter = JaegerGrpcSpanExporter.builder()
  .setEndpoint("localhost:3336")
  .setTimeout(30, TimeUnit.SECONDS)
  .build();

SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
  .addSpanProcessor(BatchSpanProcessor.builder(jaegerExporter).build())
  .build();

Metrics SDK

The application has to install a metric reader with an exporter, and may further customize the behavior of the OpenTelemetry SDK.

For example, a basic configuration instantiates the SDK meter provider and sets to export the metrics to a logging stream.

SdkMeterProvider meterProvider = SdkMeterProvider.builder()
  .registerMetricReader(PeriodicMetricReader.builder(LoggingMetricExporter.create()).build())
  .build();

Metric Reader

Metric readers read aggregated metrics.

SdkMeterProvider meterProvider = SdkMeterProvider.builder()
  .registerMetricReader(...)
  .build();

OpenTelemetry provides a variety of metric readers out of the box:

  • PeriodicMetricReader: reads metrics on a configurable interval and pushes to a MetricExporter.
  • InMemoryMetricReader: reads metrics into memory, useful for debugging and testing.
  • PrometheusHttpServer (alpha): an HTTP server that reads metrics and serializes to Prometheus text format.

Custom metric reader implementations are not currently supported.

Exporter

The PeriodicMetricReader is paired with a metric exporter, which is responsible for sending the telemetry data to a particular backend. OpenTelemetry provides the following exporters out of the box:

  • InMemoryMetricExporter: keeps the data in memory, useful for testing and debugging.
  • Logging Exporter: saves the telemetry data into log streams. Varieties include LoggingMetricExporter and OtlpJsonLoggingMetricExporter.
  • OpenTelemetry Protocol Exporter: sends the data in OTLP to the OpenTelemetry Collector or other OTLP receivers. Varieties include OtlpGrpcMetricExporter and OtlpHttpMetricExporter.

Other exporters can be found in the OpenTelemetry Registry.

Views

Views provide a mechanism for controlling how measurements are aggregated into metrics. They consist of an InstrumentSelector and a View. The instrument selector consists of a series of options for selecting which instruments the view applies to. Instruments can be selected by a combination of name, type, meter name, meter version, and meter schema URL. The view describes how measurement should be aggregated. The view can change the name, description, the aggregation, and define the set of attribute keys that should be retained.

SdkMeterProvider meterProvider = SdkMeterProvider.builder()
  .registerView(
    InstrumentSelector.builder()
      .setName("my-counter") // Select instrument(s) called "my-counter"
      .build(),
    View.builder()
      .setName("new-counter-name") // Change the name to "new-counter-name"
      .build())
  .registerMetricReader(...)
  .build()

Every instrument has a default view, which retains the original name, description, and attributes, and has a default aggregation that is based on the type of instrument. When a registered view matches an instrument, the default view is replaced by the registered view. Additional registered views that match the instrument are additive, and result in multiple exported metrics for the instrument.

Logs SDK

The logs SDK dictates how logs are processed when using the direct to collector workflow. No log SDK is needed when using the log forwarding workflow.

The typical log SDK configuration installs a log record processor and exporter. For example, the following installs the BatchLogRecordProcessor, which periodically exports to a network location via the OtlpGrpcLogRecordExporter:

SdkLoggerProvider loggerProvider = SdkLoggerProvider.builder()
  .addLogRecordProcessor(
    BatchLogRecordProcessor.builder(
      OtlpGrpcLogRecordExporter.builder()
          .setEndpoint("http://localhost:4317")
          .build())
      .build())
  .build();

LogRecord Processor

LogRecord processors process LogRecords emitted by log appenders.

OpenTelemetry provides the following LogRecord processors out of the box:

  • BatchLogRecordProcessor: periodically sends batches of LogRecords to a LogRecordExporter.
  • SimpleLogRecordProcessor: immediately sends each LogRecord to a LogRecordExporter.

Custom LogRecord processors are supported by implementing the LogRecordProcessor interface. Common use cases include enriching the LogRecords with contextual data like baggage, or filtering / obfuscating sensitive data.

LogRecord Exporter

BatchLogRecordProcessor and SimpleLogRecordProcessor are paired with LogRecordExporter, which is responsible for sending telemetry data to a particular backend. OpenTelemetry provides the following exporters out of the box:

  • OpenTelemetry Protocol Exporter: sends the data in OTLP to the OpenTelemetry Collector or other OTLP receivers. Varieties include OtlpGrpcLogRecordExporter and OtlpHttpLogRecordExporter.
  • InMemoryLogRecordExporter: keeps the data in memory, useful for testing and debugging.
  • Logging Exporter: saves the telemetry data into log streams. Varieties include SystemOutLogRecordExporter and OtlpJsonLoggingLogRecordExporter. Note: OtlpJsonLoggingLogRecordExporter logs to JUL, and may cause infinite loops (i.e. JUL -> SLF4J -> Logback -> OpenTelemetry Appender -> OpenTelemetry Log SDK -> JUL) if not carefully configured.

Custom exporters are supported by implementing the LogRecordExporter interface.

Autoconfiguration

Instead of manually creating the OpenTelemetry instance by using the SDK builders directly from your code, it is also possible to use the SDK autoconfiguration extension through the opentelemetry-sdk-extension-autoconfigure module.

This module is made available by adding the following dependency to your application.

<dependency>
    <groupId>io.opentelemetry</groupId>
    <artifactId>opentelemetry-sdk-extension-autoconfigure</artifactId>
</dependency>

It allows you to autoconfigure the OpenTelemetry SDK based on a standard set of supported environment variables and system properties. Each environment variable has a corresponding system property named the same way but as lower case and using the . (dot) character instead of the _ (underscore) as separator.

The logical service name can be specified via the OTEL_SERVICE_NAME environment variable (or otel.service.name system property).

The traces, metrics or logs exporters can be set via the OTEL_TRACES_EXPORTER, OTEL_METRICS_EXPORTER and OTEL_LOGS_EXPORTER environment variables. For example OTEL_TRACES_EXPORTER=jaeger configures your application to use the Jaeger exporter. The corresponding Jaeger exporter library has to be provided in the classpath of the application as well.

If you use the console or logging exporter for metrics, consider temporarily setting OTEL_METRIC_EXPORT_INTERVAL to a small value like 15000 (milliseconds) while testing that your metrics are properly recorded. Remember to remove the setting once you are done testing.

It’s also possible to set up the propagators via the OTEL_PROPAGATORS environment variable, like for example using the tracecontext value to use W3C Trace Context.

For more details, see all the supported configuration options in the module’s README.

The SDK autoconfiguration has to be initialized from your code in order to allow the module to go through the provided environment variables (or system properties) and set up the OpenTelemetry instance by using the builders internally.

OpenTelemetrySdk sdk = AutoConfiguredOpenTelemetrySdk.initialize()
    .getOpenTelemetrySdk();

When environment variables or system properties are not sufficient, you can use some extension points provided through the autoconfigure SPI and several methods in the AutoConfiguredOpenTelemetrySdk class.

Following an example with a code snippet for adding an additional custom span processor.

AutoConfiguredOpenTelemetrySdk.builder()
        .addTracerProviderCustomizer(
            (sdkTracerProviderBuilder, configProperties) ->
                sdkTracerProviderBuilder.addSpanProcessor(
                    new SpanProcessor() { /* implementation omitted for brevity */ }))
        .build();

SDK Logging and Error Handling

OpenTelemetry uses java.util.logging to log information about OpenTelemetry, including errors and warnings about misconfigurations or failures exporting data.

By default, log messages are handled by the root handler in your application. If you have not installed a custom root handler for your application, logs of level INFO or higher are sent to the console by default.

You may want to change the behavior of the logger for OpenTelemetry. For example, you can reduce the logging level to output additional information when debugging, increase the level for a particular class to ignore errors coming from that class, or install a custom handler or filter to run custom code whenever OpenTelemetry logs a particular message.

Examples

## Turn off all OpenTelemetry logging
io.opentelemetry.level = OFF
## Turn off logging for just the BatchSpanProcessor
io.opentelemetry.sdk.trace.export.BatchSpanProcessor.level = OFF
## Log "FINE" messages for help in debugging
io.opentelemetry.level = FINE

## Sets the default ConsoleHandler's logger's level
## Note this impacts the logging outside of OpenTelemetry as well
java.util.logging.ConsoleHandler.level = FINE

For more fine-grained control and special case handling, custom handlers and filters can be specified with code.

// Custom filter which does not log errors that come from the export
public class IgnoreExportErrorsFilter implements Filter {

 public boolean isLoggable(LogRecord record) {
    return !record.getMessage().contains("Exception thrown by the export");
 }
}
## Registering the custom filter on the BatchSpanProcessor
io.opentelemetry.sdk.trace.export.BatchSpanProcessor = io.opentelemetry.extension.logging.IgnoreExportErrorsFilter