Zero-Code Telemetry with OpenTelemetry

A demo project showing how to add distributed tracing to a Java/Spring Boot API using the OpenTelemetry Java agent — no changes to application source code required.

Architecture

React Frontend (port 80)
        ↓
Spring Boot API (port 8080)
        ↓  OTLP/HTTP :4318
OTel Collector (ports 4317, 4318)
        ↓  OTLP/gRPC :4317
Jaeger (port 16686)

Service	Description
obi-test-app	React + TypeScript frontend
obi-test-api	Spring Boot 3 REST API
otel-collector	OpenTelemetry Collector — receives and forwards telemetry
jaeger	Trace storage and UI

Running the Project

docker compose up --build

URL	Description
http://localhost	React frontend
http://localhost:8080	Spring Boot API
http://localhost:16686	Jaeger UI

Generating Traces

Hit any API endpoint to produce traces, then search for obi-test-api in the Jaeger service dropdown.

Successful requests:

curl http://localhost:8080/users
curl http://localhost:8080/posts
curl http://localhost:8080/posts/1

Error scenario (triggers a NoSuchElementException, visible as a red span in Jaeger):

curl http://localhost:8080/posts/999

How It Works

The OTel Java agent JAR is downloaded at Docker build time and attached to the JVM via -javaagent. No code changes are needed in the Spring Boot application — the agent instruments HTTP requests, responses, and exceptions automatically.

The agent is configured entirely through environment variables in docker-compose.yml:

OTEL_SERVICE_NAME=obi-test-api
OTEL_EXPORTER_OTLP_ENDPOINT=http://otel-collector:4318