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Java Agent Declarative Configuration Example

This example demonstrates how to use declarative configuration with the OpenTelemetry Java Agent to configure tracing behavior.

The configuration file is located at otel-agent-config.yaml.

This Spring Boot application includes three endpoints:

  • /actuator/health - A health check endpoint (from Spring Boot Actuator) that is configured to be excluded from tracing
  • /api/example - A simple API endpoint that will be traced normally
  • /api/remote - An endpoint that makes an outgoing HTTP (client) call, used to demonstrate peer service mapping

End-to-End Instructions

Prerequisites

  • Java 17 or higher (due to Spring Boot 3 requirement, not because of declarative config support)
  • OpenTelemetry Java Agent JAR file (see next step)

Download the OpenTelemetry Java Agent:

# Download the latest OpenTelemetry Java Agent
curl -L -o opentelemetry-javaagent.jar https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases/latest/download/opentelemetry-javaagent.jar

Step 1: Build the Application

# Build the JAR - Run from the javaagent-declarative-configuration directory
../gradlew bootJar

Step 2: Run with OpenTelemetry Java Agent

# From the javaagent-declarative-configuration directory

# Run with the OpenTelemetry Java Agent and contrib extension
java -javaagent:opentelemetry-javaagent.jar \
     -Dotel.config.file=$(pwd)/otel-agent-config.yaml \
     -jar build/libs/javaagent-declarative-configuration.jar

Step 3: Test the Endpoints

Open a new terminal and test both endpoints:

# This endpoint will NOT be traced (excluded by configuration)
curl http://localhost:8080/actuator/health

# This endpoint WILL be traced normally
curl http://localhost:8080/api/example

# This endpoint makes an outgoing client call; its client span is tagged with peer.service
curl http://localhost:8080/api/remote

Step 4: Verify Tracing Behavior

Check the application logs to see:

  • Health check requests (/actuator/health) should NOT generate traces (excluded by configuration)
  • API requests (/api/example) should generate traces with console output

Configuration

The otel-agent-config.yaml file demonstrates rule-based sampling using declarative configuration to exclude health checks from tracing:

tracer_provider:
  sampler:
    rule_based_routing:
      fallback_sampler:
        always_on:
      span_kind: SERVER
      rules:
        - action: DROP
          attribute: url.path
          pattern: /actuator.*

This configuration:

  • Uses the rule_based_routing sampler from the OpenTelemetry contrib extension
  • Excludes health check endpoints (/actuator.*) from tracing using the DROP action
  • Samples all other requests using the always_on fallback sampler
  • Only applies to SERVER span kinds

Peer service mapping

The otel-agent-config.yaml file also demonstrates peer service mapping, which maps the peer address (host name or IP) of an outgoing client call to a logical service name:

instrumentation/development:
  java:
    common:
      service_peer_mapping:
        - peer: localhost
          service_name: example-backend

This configuration:

  • Replaces the otel.instrumentation.common.peer-service-mapping system property
  • Adds a peer.service attribute to client spans whose peer address (server.address) matches a configured peer. The port is optional — omitting it matches any port.
  • In this example, the /api/remote endpoint calls back into the application over localhost, so its client span is tagged with peer.service=example-backend