GH-3402: Fix KafkaAdmin clusterId config with observability enabled

Fixes: #3402

Re-set clusterId after creating new KafkaAdmin to ensure proper
configuration when observability is enabled and bootstrap supplier
is not set.

This addresses the issue where kafkaAdmin clusterId configuration
was being ignored under specific conditions.

 **Auto-cherry-pick to `3.2.x` & `3.1.x`**

Author: varmenise

spring-kafka/src/main/java/org/springframework/kafka/core/KafkaAdmin.java

@@ -71,6 +71,9 @@
  *
  * @author Gary Russell
  * @author Artem Bilan
+ * @author Adrian Gygax
+ * @author Sanghyeok An
+ * @author Valentina Armenise
  *
  * @since 1.3
  */
@@ -208,6 +211,15 @@ public void setClusterId(String clusterId) {
 		this.clusterId = clusterId;
 	}
 
+	/**
+	 * Get the clusterId property.
+	 * @return the cluster id.
+	 * @since 3.1.8
+	 */
+	public String getClusterId() {
+		return this.clusterId;
+	}
+
 	@Override
 	public Map<String, Object> getConfigurationProperties() {
 		Map<String, Object> configs2 = new HashMap<>(this.configs);

spring-kafka/src/main/java/org/springframework/kafka/core/KafkaTemplate.java

@@ -102,6 +102,7 @@
  * @author Thomas Strauß
  * @author Soby Chacko
  * @author Gurps Bassi
+ * @author Valentina Armenise
  */
 public class KafkaTemplate<K, V> implements KafkaOperations<K, V>, ApplicationContextAware, BeanNameAware,
 		ApplicationListener<ContextStoppedEvent>, DisposableBean, SmartInitializingSingleton {
@@ -486,13 +487,17 @@ public void afterSingletonsInstantiated() {
 				if (this.kafkaAdmin != null) {
 					Object producerServers = this.producerFactory.getConfigurationProperties()
 							.get(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG);
-					String adminServers = this.kafkaAdmin.getBootstrapServers();
+					String adminServers = getAdminBootstrapAddress();
 					if (!producerServers.equals(adminServers)) {
 						Map<String, Object> props = new HashMap<>(this.kafkaAdmin.getConfigurationProperties());
 						props.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, producerServers);
 						int opTo = this.kafkaAdmin.getOperationTimeout();
+						String clusterId = this.kafkaAdmin.getClusterId();
 						this.kafkaAdmin = new KafkaAdmin(props);
 						this.kafkaAdmin.setOperationTimeout(opTo);
+						if (clusterId != null && !clusterId.isEmpty()) {
+							this.kafkaAdmin.setClusterId(clusterId);
+						}
 					}
 				}
 			}
@@ -502,6 +507,21 @@ else if (this.micrometerEnabled) {
 		}
 	}
 
+	private String getAdminBootstrapAddress() {
+		// Retrieve bootstrap servers from KafkaAdmin bootstrap supplier if available
+		String adminServers = this.kafkaAdmin.getBootstrapServers();
+
+		// Fallback to configuration properties if bootstrap servers are not set
+		if (adminServers == null) {
+			adminServers = this.kafkaAdmin.getConfigurationProperties().getOrDefault(
+					AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG,
+					""
+			).toString();
+		}
+
+		return adminServers;
+	}
+
 	@Nullable
 	private String clusterId() {
 		if (this.kafkaAdmin != null && this.clusterId == null) {