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.
2026-09-04 10:40:04 +05:30
commit 4b6cefa60a
64 changed files with 3195 additions and 0 deletions
--- a/docs/output/07-custom-health-indicators.txt
+++ b/docs/output/07-custom-health-indicators.txt
@@ -0,0 +1,121 @@
+### profile: details    (show-details: always, show-components: always)
+
+--- upstream UP ---
+$ curl -s -o /dev/null -w '%{http_code}' http://localhost:8080/actuator/health
+  HTTP 503
+{
+    "components": {
+        "db": {
+            "details": {
+                "database": "H2",
+                "validationQuery": "isValid()"
+            },
+            "status": "UP"
+        },
+        "diskSpace": {
+            "details": {
+                "total": 10213466112,
+                "free": 3877675008,
+                "threshold": 10485760,
+                "path": "/tmp/work/spring-boot-demo/.",
+                "exists": true
+            },
+            "status": "UP"
+        },
+        "externalApi": {
+            "details": {
+                "url": "http://localhost:8080/stub/upstream/ping",
+                "response": "pong",
+                "latencyMs": 66,
+                "timeoutMs": 750
+            },
+            "status": "UP"
+        },
+        "kafka": {
+            "details": {
+                "bootstrap": "localhost:9092",
+                "tuned": true,
+                "error": "TimeoutException: null",
+                "probeMs": 1500,
+                "budgetMs": 1500
+            },
+            "status": "DOWN"
+        },
+        "livenessState": {
+            "status": "UP"
+        },
+        "ordersDatabase": {
+            "details": {
+                "orders": 3,
+                "queryMs": 0,
+                "slowThresholdMs": 250
+            },
+            "status": "UP"
+        },
+        "ping": {
+            "status": "UP"
+        },
+        "readinessState": {
+            "status": "UP"
+        },
+        "ssl": {
+            "details": {
+                "expiringChains": [],
+                "invalidChains": [],
+                "validChains": []
+            },
+            "status": "UP"
+        }
+    },
+    "groups": [
+        "liveness",
+        "readiness"
+    ],
+    "status": "DOWN"
+}
+
+--- flip the upstream to DOWN, change nothing else ---
+$ curl -s -X POST 'http://localhost:8080/stub/upstream/mode?value=down'
+upstream mode = DOWN
+  HTTP 503
+{
+  "status": "DOWN",
+  "externalApi": {
+    "details": {
+      "error": "org.springframework.web.client.HttpServerErrorException$ServiceUnavailable: 503 : \"upstream unavailable\"",
+      "url": "http://localhost:8080/stub/upstream/ping",
+      "latencyMs": 67,
+      "timeoutMs": 750
+    },
+    "status": "DOWN"
+  }
+}
+
+  The aggregate went DOWN and /actuator/health now answers 503. If that URL is your
+  Kubernetes readiness probe, every pod in the deployment has just left the load
+  balancer because a third party had a bad minute.
+
+--- a single component, addressed directly ---
+$ curl -s http://localhost:8080/actuator/health/ordersDatabase
+{
+    "details": {
+        "orders": 3,
+        "queryMs": 0,
+        "slowThresholdMs": 250
+    },
+    "status": "UP"
+}
+$ curl -s http://localhost:8080/actuator/health/kafka
+{
+    "details": {
+        "bootstrap": "localhost:9092",
+        "tuned": true,
+        "error": "TimeoutException: null",
+        "probeMs": 1500,
+        "budgetMs": 1500
+    },
+    "status": "DOWN"
+}
+
+--- restore ---
+upstream mode = UP