opentelemetry-java-instrumentation

If you run Java apps and want observability (traces, metrics, logs) without rewriting your code, this is how you get it. One JAR file, one JVM flag, and it auto-instruments your Spring Boot, Kafka, gRPC, JDBC, and dozens of other libraries. Zero code changes. CNCF project, Apache 2.0, completely free.

The agent itself is trivial to deploy. Add it to your JVM startup, point it at an OTLP endpoint, done. The real ops burden is the backend: you need somewhere to send the data. OpenTelemetry Collector plus Jaeger or Grafana Tempo is the common self-hosted stack. That's a meaningful setup, but it's a one-time cost shared across all your services.

Solo devs and small teams can point it at a managed backend (Grafana Cloud free tier, Honeycomb, Datadog) and skip the infrastructure entirely. Larger teams running their own Grafana/Tempo stack get full control and zero per-host licensing. The agent is vendor-neutral by design, so you're never locked to one backend.

The catch: it's Java-only. If you're running a polyglot stack, you need separate OpenTelemetry agents for Python, Node, Go, etc. And "zero code changes" means "zero code changes until you need custom spans," at which point you're adding SDK calls anyway.