Observability means being able to answer “what’s wrong and why” from the outside — without modifying the code. The three pillars: metrics (what happened), logs (what the code did), and traces (how a request flowed). This article wires them all together. The Stack Spring Boot App ├── Metrics → Micrometer → Prometheus scrape → Grafana dashboards ├── Traces → Micrometer Tracing → OTLP → Tempo → Grafana trace view └── Logs → Logback → Loki4j → Loki → Grafana log explorer All three converge in Grafana — click a metric spike to see the correlated logs and traces for that exact time window.

Observability means you can answer “what is wrong and why” from your system’s outputs alone — without adding new instrumentation after an incident. It requires three types of data: metrics (what happened), traces (why it happened), and logs (the details). Spring Boot 4 ships a single OpenTelemetry starter that covers all three. This guide shows how to wire up the complete observability stack: Prometheus + Grafana for metrics, Grafana Tempo for distributed tracing, and Grafana Loki for logs.