Disable Elasticsearch client's sniffer by default

This commit switches the auto-configuration of Elasticsearch to not
contribute a client's sniffer by default.

This matches the best practices as describe in
https://www.elastic.co/blog/elasticsearch-sniffing-best-practices-what-when-why-how

Closes gh-48155

Author: snicoll

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/data/nosql.adoc

@@ -341,7 +341,7 @@ To take full control over the client's configuration, define a javadoc:co.elasti
 
 
 
-Additionally, a javadoc:co.elastic.clients.transport.rest5_client.low_level.sniffer.Sniffer[] is auto-configured to automatically discover nodes from a running Elasticsearch cluster and set them on the javadoc:co.elastic.clients.transport.rest5_client.low_level.Rest5Client[] bean.
+Additionally, a javadoc:co.elastic.clients.transport.rest5_client.low_level.sniffer.Sniffer[] can be auto-configured to automatically discover nodes from a running Elasticsearch cluster and set them on the javadoc:co.elastic.clients.transport.rest5_client.low_level.Rest5Client[] bean.
 You can further tune how javadoc:co.elastic.clients.transport.rest5_client.low_level.sniffer.Sniffer[] is configured, as shown in the following example:
 
 [configprops,yaml]
@@ -350,12 +350,11 @@ spring:
   elasticsearch:
     restclient:
       sniffer:
+        enabled: true
         interval: "10m"
         delay-after-failure: "30s"
 ----
 
-To disable auto-configuration of the Sniffer, set configprop:spring.elasticsearch.restclient.sniffer.enabled[] to `false`.
-
 
 
 [[data.nosql.elasticsearch.connecting-using-rest.javaapiclient]]

module/spring-boot-elasticsearch/src/main/java/org/springframework/boot/elasticsearch/autoconfigure/ElasticsearchProperties.java

@@ -163,7 +163,7 @@ public static class Sniffer {
 			/**
 			 * Whether the sniffer is enabled.
 			 */
-			private boolean enabled = true;
+			private boolean enabled;
 
 			/**
 			 * Interval between consecutive ordinary sniff executions.

module/spring-boot-elasticsearch/src/main/java/org/springframework/boot/elasticsearch/autoconfigure/ElasticsearchRestClientConfigurations.java

@@ -139,7 +139,7 @@ Rest5Client elasticsearchRestClient(Rest5ClientBuilder restClientBuilder) {
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Sniffer.class)
 	@ConditionalOnSingleCandidate(Rest5Client.class)
-	@ConditionalOnProperty(name = "spring.elasticsearch.restclient.sniffer.enabled", matchIfMissing = true)
+	@ConditionalOnProperty(name = "spring.elasticsearch.restclient.sniffer.enabled")
 	static class RestClientSnifferConfiguration {
 
 		@Bean

module/spring-boot-elasticsearch/src/test/java/org/springframework/boot/elasticsearch/autoconfigure/ElasticsearchRestClientAutoConfigurationTests.java

@@ -257,8 +257,13 @@ void configureWithCustomSocketKeepAlive() {
 	}
 
 	@Test
-	void configureShouldCreateSnifferUsingRest5Client() {
-		this.contextRunner.run((context) -> {
+	void configureShouldNotCreateSnifferUsingRest5ClientByDefault() {
+		this.contextRunner.run((context) -> assertThat(context).doesNotHaveBean(Sniffer.class));
+	}
+
+	@Test
+	void configureWithSnifferEnabled() {
+		this.contextRunner.withPropertyValues("spring.elasticsearch.restclient.sniffer.enabled=true").run((context) -> {
 			assertThat(context).hasSingleBean(Sniffer.class);
 			assertThat(context.getBean(Sniffer.class)).hasFieldOrPropertyWithValue("restClient",
 					context.getBean(Rest5Client.class));
@@ -272,7 +277,8 @@ void configureShouldCreateSnifferUsingRest5Client() {
 	@Test
 	void configureWithCustomSnifferSettings() {
 		this.contextRunner
-			.withPropertyValues("spring.elasticsearch.restclient.sniffer.interval=180s",
+			.withPropertyValues("spring.elasticsearch.restclient.sniffer.enabled=true",
+					"spring.elasticsearch.restclient.sniffer.interval=180s",
 					"spring.elasticsearch.restclient.sniffer.delay-after-failure=30s")
 			.run((context) -> {
 				assertThat(context).hasSingleBean(Sniffer.class);
@@ -287,18 +293,14 @@ void configureWithCustomSnifferSettings() {
 	@Test
 	void configureWhenCustomSnifferShouldBackOff() {
 		Sniffer customSniffer = mock(Sniffer.class);
-		this.contextRunner.withBean(Sniffer.class, () -> customSniffer).run((context) -> {
-			assertThat(context).hasSingleBean(Sniffer.class);
-			Sniffer sniffer = context.getBean(Sniffer.class);
-			assertThat(sniffer).isSameAs(customSniffer);
-			then(customSniffer).shouldHaveNoInteractions();
-		});
-	}
-
-	@Test
-	void configureWithSnifferDisabled() {
-		this.contextRunner.withPropertyValues("spring.elasticsearch.restclient.sniffer.enabled=false")
-			.run((context) -> assertThat(context).doesNotHaveBean(Sniffer.class));
+		this.contextRunner.withPropertyValues("spring.elasticsearch.restclient.sniffer.enabled=true")
+			.withBean(Sniffer.class, () -> customSniffer)
+			.run((context) -> {
+				assertThat(context).hasSingleBean(Sniffer.class);
+				Sniffer sniffer = context.getBean(Sniffer.class);
+				assertThat(sniffer).isSameAs(customSniffer);
+				then(customSniffer).shouldHaveNoInteractions();
+			});
 	}
 
 	@Test