feat: add cameleer3-server startup connectivity check

src/main/java/net/siegeln/cameleer/saas/observability/ConnectivityHealthCheck.java

@@ -0,0 +1,48 @@
+package net.siegeln.cameleer.saas.observability;
+
+import net.siegeln.cameleer.saas.runtime.RuntimeConfig;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.context.event.ApplicationReadyEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.stereotype.Component;
+import org.springframework.web.client.RestClient;
+
+@Component
+public class ConnectivityHealthCheck {
+
+    private static final Logger log = LoggerFactory.getLogger(ConnectivityHealthCheck.class);
+
+    private final RuntimeConfig runtimeConfig;
+
+    public ConnectivityHealthCheck(RuntimeConfig runtimeConfig) {
+        this.runtimeConfig = runtimeConfig;
+    }
+
+    @EventListener(ApplicationReadyEvent.class)
+    public void verifyConnectivity() {
+        checkCameleer3Server();
+    }
+
+    private void checkCameleer3Server() {
+        try {
+            var client = RestClient.builder()
+                    .baseUrl(runtimeConfig.getCameleer3ServerEndpoint())
+                    .build();
+            var response = client.get()
+                    .uri("/actuator/health")
+                    .retrieve()
+                    .toBodilessEntity();
+            if (response.getStatusCode().is2xxSuccessful()) {
+                log.info("cameleer3-server connectivity: OK ({})",
+                        runtimeConfig.getCameleer3ServerEndpoint());
+            } else {
+                log.warn("cameleer3-server connectivity: HTTP {} ({})",
+                        response.getStatusCode(), runtimeConfig.getCameleer3ServerEndpoint());
+            }
+        } catch (Exception e) {
+            log.warn("cameleer3-server connectivity: FAILED ({}) - {}",
+                    runtimeConfig.getCameleer3ServerEndpoint(), e.getMessage());
+        }
+    }
+}