Spring Boot 4 Actuator in production: endpoints, security, custom health indicators

Companion repository for the ankurm.com article. Every transcript in docs/output/
was produced by running this project; scripts/run-all.sh regenerates all of them.

Verified against Spring Boot 4.1.1 / Framework 7.0.9 / Security 7.1.1 /
Micrometer 1.17.1 / kafka-clients 4.2.1 on Temurin JDK 25.0.4.1+1.

docs/output/10-slow-upstream.txt

@@ -0,0 +1,18 @@
+### profile: details    upstream deliberately sleeping 30s per request
+### demo.upstream.timeout-ms = 750, so the indicator gives up long before the stub replies
+
+$ time curl -s http://localhost:8080/actuator/health/externalApi
+{
+    "details": {
+        "error": "org.springframework.web.client.ResourceAccessException: I/O error on GET request for \"http://localhost:8080/stub/upstream/ping\": Read timed out",
+        "url": "http://localhost:8080/stub/upstream/ping",
+        "latencyMs": 753,
+        "timeoutMs": 750
+    },
+    "status": "DOWN"
+}
+wall clock: 0.84 s
+
+  The read timeout is what bounds this, not the endpoint. Remove setReadTimeout from
+  ExternalApiHealthIndicator and this call blocks for the full 30 seconds, holding a
+  Tomcat worker the whole time.