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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/env-var-proof/README.md
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# env-var-proof
Answers one factual question with real execution instead of quoting a changelog: does Spring
Boot 4.1 actually honor standard `OTEL_*` environment variables that Boot 4.0 did not?
`boot40/` and `boot41/` contain the **identical** `OtelEnvProofApplication.java` -- the only
difference between the two Maven modules is the `spring-boot-starter-parent` version (4.0.8 vs
4.1.1). Both start with only `OTEL_EXPORTER_OTLP_ENDPOINT` and `OTEL_METRIC_EXPORT_INTERVAL` set
(no `management.otlp.*` Spring properties anywhere) and point at `stub-receiver/`, a
dependency-free stand-in for an OTLP collector that just logs every POST it receives.
See [`../docs/output/04-otel-env-vars-4.0-vs-4.1.txt`](../docs/output/04-otel-env-vars-4.0-vs-4.1.txt)
for the captured result, and [`../docs/03-otel-env-vars.md`](../docs/03-otel-env-vars.md) for the
write-up. Run it yourself with [`../scripts/run-env-var-proof.sh`](../scripts/run-env-var-proof.sh).