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

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).
2026-09-18 09:32:34 +00:00
parent 320733265f
commit 03bdf7ee87
28 changed files with 1027 additions and 2 deletions
@@ -0,0 +1,43 @@
+Identical Java source (env-var-proof/OtelEnvProofApplication.java), compiled twice against two
+different spring-boot-starter-parent versions -- 4.0.8 and 4.1.1 -- run with ONLY standard OTEL_*
+environment variables set (zero management.otlp.* Spring properties anywhere), against a
+minimal stand-in OTLP receiver that just logs every POST it gets:
+
+  OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:PORT
+  OTEL_METRIC_EXPORT_INTERVAL=2000
+
+--- Spring Boot 4.1.1 ---
+
+  Publishing metrics for OtlpMeterRegistry every 2s to http://localhost:PORT/v1/metrics ...
+
+  receiver log (20s window):
+  ... POST /v1/metrics content-length=8247   (x11, one every ~2s)
+
+  Both the endpoint AND the interval standard env vars were honored.
+
+--- Spring Boot 4.0.8, same two env vars ---
+
+  Publishing metrics for OtlpMeterRegistry every 1m to http://localhost:PORT/v1/metrics ...
+
+  receiver log (20s window):
+  ... POST /v1/metrics content-length=8247   (x1, at JVM shutdown only)
+
+  The endpoint env var was honored (Micrometer's own OtlpConfig has long fallen back to
+  OTEL_EXPORTER_OTLP_ENDPOINT independent of Spring Boot's own property binding). The interval
+  env var was NOT -- the exporter still logs "every 1m", the JVM's own default, and the only POST
+  the receiver saw was the one every PushMeterRegistry fires on shutdown regardless of interval.
+
+--- Spring Boot 4.0.8, old-style Spring property instead ---
+
+  MANAGEMENT_OTLP_METRICS_EXPORT_URL=http://localhost:PORT/v1/metrics
+  MANAGEMENT_OTLP_METRICS_EXPORT_STEP=2s
+
+  Publishing metrics for OtlpMeterRegistry every 2s to http://localhost:PORT/v1/metrics ...
+
+  receiver log (20s window):
+  ... POST /v1/metrics content-length=8435   (x11, one every ~2s)
+
+  Boot 4.0's own management.otlp.* properties always worked for this. What's new in 4.1 is that
+  the SAME standard OTEL_* variable now works too, without a Spring-specific property to learn --
+  useful the moment the same env vars are already used to configure something else in the same
+  deployment (the OTel Collector, another language's service, docker-compose.yml).