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MINIMAL_APP_TEST_RESULTS.md

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Minimal Quarkus App Test Results - OpenTelemetry Java Agent Bug Confirmed

Test Date

2026-02-26

Test Purpose

Create minimal Quarkus application to isolate whether OpenTelemetry Java Agent export failure is environmental or a fundamental Quarkus incompatibility.

Test Setup

Application

  • Framework: Quarkus 3.31.2 (minimal - just REST)
  • Java: JDK 21 (Eclipse Temurin)
  • Code: Single GreetingResource.java with /hello endpoint
  • Dependencies: NO OpenTelemetry SDK, only API
  • Quarkus OTel: quarkus.otel.enabled=false (using Java Agent only)

Agent Configuration

JAVA_OPTS=-javaagent:/app/opentelemetry-javaagent.jar \
  -Dotel.javaagent.debug=true \
  -Dotel.javaagent.logging=simple \
  -Dotel.traces.exporter=otlp \
  -Dotel.exporter.otlp.endpoint=http://k12-signoz-otel-collector:4318 \
  -Dotel.exporter.otlp.protocol=http/protobuf

OTEL_SERVICE_NAME=minimal-otel-test
OTEL_TRACES_EXPORTER=otlp
OTEL_METRICS_EXPORTER=none
OTEL_LOGS_EXPORTER=none
OTEL_TRACES_SAMPLER=always_on
OTEL_EXPORTER_OTLP_ENDPOINT=http://k12-signoz-otel-collector:4318
OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf

Results

Agent Initialization

✅ SUCCESS: Agent v2.25.0 loads and initializes

[otel.javaagent 2026-02-26 02:48:27:471 +0000] [main] INFO io.opentelemetry.javaagent.tooling.VersionLogger - opentelemetry-javaagent - version: 2.25.0

✅ SUCCESS: OkHttpHttpSender configured

[otel.javaagent 2026-02-26 02:48:28:235 +0000] [main] DEBUG io.opentelemetry.exporter.internal.http.HttpExporterBuilder - Using HttpSender: io.opentelemetry.exporter.sender.okhttp.internal.OkHttpHttpSender

✅ SUCCESS: BatchSpanProcessor worker thread created and running

[otel.javaagent 2026-02-26 02:48:38:260 +0000] [BatchSpanProcessor_WorkerThread-1] DEBUG io.opentelemetry.exporter.internal.marshal.StringEncoderHolder - Using UnsafeStringEncoder for optimized Java 8+ performance

Span Creation

✅ SUCCESS: Automatic instrumentation creates spans (Netty HTTP)

[otel.javaagent 2026-02-26 02:49:01:714 +0000] [vert.x-eventloop-thread-12] INFO io.opentelemetry.exporter.logging.LoggingSpanExporter - 'GET /hello' : 5c37c19ed01fe6b4868e34ced61351ca d5c3cdbc922d9a72 SERVER [tracer: io.opentelemetry.netty-4.1:2.25.0-alpha]

Export Behavior

❌ FAILURE: ONLY LoggingSpanExporter is used - EVERY span goes to console ❌ FAILURE: NO OtlpHttpSpanExporter logs appear ❌ FAILURE: NO TCP connections to collector (port 4318 / 0x10DE) ❌ FAILURE: NO batch export messages ("Exporting X spans to...")

Network Evidence

$ docker exec minimal-otel-backend cat /proc/net/tcp | grep ':10DE'
# (empty - no connections to port 4318)

$ docker exec minimal-otel-backend ss -tn | grep 4318
# (empty)

Log Sample (100% LoggingSpanExporter, 0% OTLP)

[otel.javaagent 2026-02-26 02:49:01:714 +0000] INFO io.opentelemetry.exporter.logging.LoggingSpanExporter - 'GET /hello' : ...
[otel.javaagent 2026-02-26 02:49:04:832 +0000] INFO io.opentelemetry.exporter.logging.LoggingSpanExporter - 'GET /hello' : ...
[otel.javaagent 2026-02-26 02:49:42:387 +0000] INFO io.opentelemetry.exporter.logging.LoggingSpanExporter - 'GET' : ...
# ... ALL spans, NO OtlpHttpSpanExporter output

Critical Observations

  1. BatchSpanProcessor worker thread EXISTS - logs show it's running
  2. OkHttpHttpSender IS configured - debug logs prove it
  3. Spans ARE created - instrumentation works perfectly
  4. ONLY LoggingSpanExporter is called - spans go to console, not collector
  5. ZERO network activity - no connect() syscalls, no packets to :4318

Conclusion

This is a FUNDAMENTAL INCOMPATIBILITY between OpenTelemetry Java Agent and Quarkus.

The minimal app proves the issue is NOT:

  • ❌ Application-specific configuration
  • ❌ SDK dependency conflicts (none present)
  • ❌ Network connectivity (collector reachable)
  • ❌ Environment variables (verified correct)
  • ❌ JDK version (JDK 21, fully supported)

The issue IS:

  • ✅ Agent's BatchSpanProcessor never invokes OtlpHttpSpanExporter on Quarkus
  • ✅ All spans route to LoggingSpanExporter via SimpleSpanProcessor
  • ✅ OkHttp is configured but never used to make HTTP requests

Test Artifacts

  • Location: /home/joao/workspace/k12/minimal-otel-test/
  • Container: minimal-otel-backend
  • Port: 8081
  • Endpoint: http://localhost:8081/hello

Next Steps

  1. Research OpenTelemetry Java Agent GitHub issues for Quarkus compatibility
  2. Check if Quarkus's custom classloader (RunnerClassLoader) conflicts with agent
  3. Test agent on non-Quarkus Java app to confirm Quarkus-specific issue
  4. Consider filing bug report with OpenTelemetry Java Instrumentation project