fix(#5147): apply configured monitor timeout to StatusUpdater

spring-boot-admin-server/src/main/java/de/codecentric/boot/admin/server/config/AdminServerAutoConfiguration.java

@@ -100,7 +100,22 @@ public InstanceIdGenerator instanceIdGenerator() {
 	@ConditionalOnMissingBean
 	public StatusUpdater statusUpdater(InstanceRepository instanceRepository,
 			InstanceWebClient.Builder instanceWebClientBuilder) {
-		return new StatusUpdater(instanceRepository, instanceWebClientBuilder.build(), new ApiMediaTypeHandler());
+
+		StatusUpdater updater = new StatusUpdater(instanceRepository, instanceWebClientBuilder.build(),
+				new ApiMediaTypeHandler());
+
+		AdminServerProperties.MonitorProperties monitorProperties = this.adminServerProperties.getMonitor();
+
+		Duration timeout = monitorProperties.getDefaultTimeout();
+		Duration interval = monitorProperties.getStatusInterval();
+
+		if (timeout.compareTo(interval) > 0) {
+			timeout = interval;
+		}
+
+		updater.timeout(timeout);
+
+		return updater;
 	}
 
 	@Bean(initMethod = "start", destroyMethod = "stop")
@@ -117,8 +132,8 @@ public StatusUpdateTrigger statusUpdateTrigger(StatusUpdater statusUpdater, Publ
 					defaultTimeout, statusInterval);
 		}
 
-		return new StatusUpdateTrigger(statusUpdater, events, monitorProperties.getStatusInterval(),
-				monitorProperties.getStatusLifetime(), monitorProperties.getStatusMaxBackoff());
+		return new StatusUpdateTrigger(statusUpdater, events, statusInterval, monitorProperties.getStatusLifetime(),
+				monitorProperties.getStatusMaxBackoff());
 	}
 
 	@Bean

spring-boot-admin-server/src/test/java/de/codecentric/boot/admin/server/MonitorTimeoutIntegrationTest.java

@@ -0,0 +1,190 @@
+/*
+ * Copyright 2014-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package de.codecentric.boot.admin.server;
+
+import java.time.Duration;
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.jspecify.annotations.NonNull;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.health.contributor.Health;
+import org.springframework.boot.health.contributor.ReactiveHealthIndicator;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.web.server.LocalServerPort;
+import org.springframework.context.annotation.Bean;
+import org.springframework.security.config.web.server.ServerHttpSecurity;
+import org.springframework.security.web.server.SecurityWebFilterChain;
+import reactor.core.publisher.Mono;
+
+import de.codecentric.boot.admin.server.config.EnableAdminServer;
+import de.codecentric.boot.admin.server.domain.entities.Instance;
+import de.codecentric.boot.admin.server.domain.entities.InstanceRepository;
+import de.codecentric.boot.admin.server.domain.values.InstanceId;
+import de.codecentric.boot.admin.server.domain.values.Registration;
+import de.codecentric.boot.admin.server.services.InstanceRegistry;
+import de.codecentric.boot.admin.server.services.StatusUpdater;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests verifying that the monitor timeout configured via
+ * {@code spring.boot.admin.monitor.default-timeout} is actually applied by
+ * {@link StatusUpdater} when polling the health endpoint (see issue #5147).
+ *
+ * <p>
+ * The test starts a minimal admin server on a random port. It registers an instance whose
+ * health endpoint is backed by a {@link SlowHealthIndicator} and directly invokes
+ * {@link StatusUpdater#updateStatus} to avoid waiting for the polling interval.
+ *
+ * <ul>
+ * <li>No artificial delay → health responds within the effective timeout → instance stays
+ * <strong>UP</strong></li>
+ * <li>5 s delay &gt; 2 s effective timeout → WebClient times out → instance goes
+ * <strong>OFFLINE</strong></li>
+ * <li>After resetting the delay → instance recovers to <strong>UP</strong></li>
+ * </ul>
+ *
+ * <p>
+ * The configured {@code default-timeout} is 3 s. {@code StatusUpdater} subtracts a 1 s
+ * margin before passing it to the WebClient, so the effective read timeout is 2 s.
+ */
+@SpringBootTest(classes = MonitorTimeoutIntegrationTest.TestAdminApplication.class,
+		webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
+		properties = { "spring.main.web-application-type=reactive", "spring.boot.admin.monitor.default-timeout=3s",
+				"spring.boot.admin.monitor.status-interval=60s", "spring.boot.admin.monitor.status-lifetime=60s",
+				"management.endpoints.web.exposure.include=health" })
+class MonitorTimeoutIntegrationTest {
+
+	@LocalServerPort
+	private int port;
+
+	@Autowired
+	private SlowHealthIndicator slowHealthIndicator;
+
+	@Autowired
+	private StatusUpdater statusUpdater;
+
+	@Autowired
+	private InstanceRegistry instanceRegistry;
+
+	@Autowired
+	private InstanceRepository instanceRepository;
+
+	private InstanceId instanceId;
+
+	@BeforeEach
+	void setUp() {
+		this.slowHealthIndicator.setDelaySeconds(0);
+		String healthUrl = "http://localhost:" + this.port + "/actuator/health";
+		this.instanceId = this.instanceRegistry.register(Registration.create("timeout-test", healthUrl).build())
+			.block();
+	}
+
+	@AfterEach
+	void tearDown() {
+		this.slowHealthIndicator.setDelaySeconds(0);
+		if (this.instanceId != null) {
+			this.instanceRegistry.deregister(this.instanceId).block();
+		}
+	}
+
+	@Test
+	void instanceIsUpWhenHealthRespondsWithinConfiguredTimeout() {
+		triggerStatusUpdate();
+
+		assertThat(findInstance().getStatusInfo().getStatus()).isEqualTo("UP");
+	}
+
+	@Test
+	void instanceGoesOfflineWhenHealthExceedsConfiguredTimeout() {
+		// 5 s delay exceeds the 2 s effective WebClient timeout (3 s configured − 1 s
+		// margin).
+		this.slowHealthIndicator.setDelaySeconds(5);
+		triggerStatusUpdate();
+
+		assertThat(findInstance().getStatusInfo().getStatus()).isEqualTo("OFFLINE");
+	}
+
+	@Test
+	void instanceRecoversWhenHealthBecomesResponsiveAgain() {
+		// Step 1: trigger a timeout → OFFLINE.
+		this.slowHealthIndicator.setDelaySeconds(5);
+		triggerStatusUpdate();
+		assertThat(findInstance().getStatusInfo().getStatus()).isEqualTo("OFFLINE");
+
+		// Step 2: remove the delay → health responds fast → UP again.
+		this.slowHealthIndicator.setDelaySeconds(0);
+		triggerStatusUpdate();
+		assertThat(findInstance().getStatusInfo().getStatus()).isEqualTo("UP");
+	}
+
+	private void triggerStatusUpdate() {
+		this.statusUpdater.updateStatus(this.instanceId).block(Duration.ofSeconds(15));
+	}
+
+	private Instance findInstance() {
+		return this.instanceRepository.find(this.instanceId).block();
+	}
+
+	@SpringBootConfiguration
+	@EnableAutoConfiguration
+	@EnableAdminServer
+	static class TestAdminApplication {
+
+		@Bean
+		SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
+			return http.authorizeExchange((authorizeExchange) -> authorizeExchange.anyExchange().permitAll())
+				.csrf(ServerHttpSecurity.CsrfSpec::disable)
+				.build();
+		}
+
+		@Bean
+		SlowHealthIndicator slowHealthIndicator() {
+			return new SlowHealthIndicator();
+		}
+
+	}
+
+	/**
+	 * A reactive health indicator that introduces a configurable delay before responding.
+	 * Used to simulate a slow downstream health endpoint for timeout verification.
+	 */
+	static class SlowHealthIndicator implements ReactiveHealthIndicator {
+
+		private final AtomicLong delaySeconds = new AtomicLong(0);
+
+		@Override
+		public @NonNull Mono<Health> health() {
+			long delay = this.delaySeconds.get();
+			if (delay <= 0) {
+				return Mono.just(Health.up().build());
+			}
+			return Mono.delay(Duration.ofSeconds(delay)).map((tick) -> Health.up().build());
+		}
+
+		void setDelaySeconds(long seconds) {
+			this.delaySeconds.set(Math.max(0, seconds));
+		}
+
+	}
+
+}

spring-boot-admin-server/src/test/java/de/codecentric/boot/admin/server/config/AdminServerAutoConfigurationTest.java

@@ -16,6 +16,8 @@
 
 package de.codecentric.boot.admin.server.config;
 
+import java.time.Duration;
+
 import com.hazelcast.config.Config;
 import org.junit.jupiter.api.Test;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
@@ -36,6 +38,7 @@
 import de.codecentric.boot.admin.server.notify.MailNotifier;
 import de.codecentric.boot.admin.server.notify.NotificationTrigger;
 import de.codecentric.boot.admin.server.notify.Notifier;
+import de.codecentric.boot.admin.server.services.StatusUpdater;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -64,6 +67,28 @@ void hazelcastConfig() {
 		});
 	}
 
+	@Test
+	void shouldApplyConfiguredTimeoutFromProperties() {
+		this.contextRunner
+			.withPropertyValues("spring.boot.admin.monitor.default-timeout=5s",
+					"spring.boot.admin.monitor.status-interval=10s")
+			.run((context) -> {
+				StatusUpdater updater = context.getBean(StatusUpdater.class);
+				assertThat(updater).extracting("timeout").isEqualTo(Duration.ofSeconds(5));
+			});
+	}
+
+	@Test
+	void shouldClampTimeoutToInterval() {
+		this.contextRunner
+			.withPropertyValues("spring.boot.admin.monitor.default-timeout=20s",
+					"spring.boot.admin.monitor.status-interval=10s")
+			.run((context) -> {
+				StatusUpdater updater = context.getBean(StatusUpdater.class);
+				assertThat(updater).extracting("timeout").isEqualTo(Duration.ofSeconds(10));
+			});
+	}
+
 	public static class TestHazelcastConfig {
 
 		@Bean