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Add observability: real OTLP metrics/traces to grafana/otel-lgtm, Docker Compose auto-wiring, and a dual-version (Boot 4.0 vs 4.1) proof of the new OTEL_* env var support

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Companion module for the rewritten ankurm.com Prometheus/Grafana monitoring post. Verified
against a real running grafana/otel-lgtm container (not mocked): 8 real requests produce a real
orders_placed_total metric queried back from the bundled Prometheus-compatible API with zero
management.otlp.* properties, auto-wired entirely by Boot's Docker Compose service-connection
detection. Two real findings surfaced along the way and documented rather than smoothed over:
@Observed silently produces no span without an explicit ObservedAspect bean (AspectJ weaving
alone is not sufficient, despite Micrometer Tracing being active), and OTEL_EXPORTER_OTLP_ENDPOINT
already worked on Boot 4.0 via Micrometer's own OtlpConfig fallback -- what's actually new in 4.1
is the rest of the standard OTEL_* surface (verified with OTEL_METRIC_EXPORT_INTERVAL against
identical source compiled on both Boot 4.0.8 and 4.1.1).

Also fixes the root README's module table, which was missing a row for
resilience4j-circuit-breaker (added in a previous commit but never indexed here).
This commit is contained in:
Claude
2026-09-18 09:32:34 +00:00
parent 320733265f
commit 03bdf7ee87
28 changed files with 1027 additions and 2 deletions
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observability/docs/04-production-checklist.md
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# 4. Production checklist
Previous: [3. OTEL_* environment variables](03-otel-env-vars.md) | [README](../README.md)
| Item | This module's finding |
|---|---|
| Which starter | `spring-boot-starter-opentelemetry` -- one dependency for OTLP metrics + traces, replacing a per-vendor registry jar plus a tracing bridge |
| Local development | A `compose.yaml` naming `grafana/otel-lgtm` gets auto-wired by Boot's Docker Compose support with zero `management.otlp.*` properties -- verified `127.0.0.1`, not the bare-default `localhost`, in the startup log |
| Any other environment | Set the export endpoint explicitly -- either `management.otlp.*` properties or, as of 4.1, standard `OTEL_EXPORTER_OTLP_*` variables. Auto-wiring is a dev-time convenience only |
| Standard `OTEL_*` env vars | `OTEL_EXPORTER_OTLP_ENDPOINT` worked before 4.1 too (a Micrometer default, not a Boot feature); the rest of the surface -- `OTEL_METRIC_EXPORT_INTERVAL` and friends -- is genuinely new in 4.1 |
| `@Observed` | Needs an explicit `ObservedAspect` @Bean. AspectJ weaving present + Micrometer Tracing active is *not* sufficient on its own -- the annotation is silently inert without it |
| Trace sampling | Defaults to 0.10. Metrics are never sampled. A "why don't my traces show up" question at low local traffic is very often just this |
| Cardinality, context propagation, the Observation API in depth | Already covered start to finish: [Micrometer to OpenTelemetry: The Spring Boot 4 Observability Guide](https://ankurm.com/micrometer-opentelemetry-spring-boot-4-observability-guide/) |
## License
MIT -- part of the [spring-boot-demo](../../) container repository; see [../../LICENSE](../../LICENSE).