Add function-based health check. Add restTemplate-based health-check beans to default config (#866)

* Switch to a function-based HealthCheckServiceInstanceListSupplier.

* Handle exception for restTemplate based function. Add default blocking health-check configuration.

* Add docs.

docs/src/main/asciidoc/spring-cloud-commons.adoc

@@ -968,6 +968,9 @@ public class CustomLoadBalancerConfiguration {
 	}
 ----
 
+TIP: For the non-reactive stack, create this supplier with the `withBlockingHealthChecks()`.
+You can also pass your own `WebClient` or `RestTemplate` instance to be used for the checks.
+
 WARNING: `HealthCheckServiceInstanceListSupplier` has its own caching mechanism based on Reactor Flux `replay()`. Therefore, if it's being used, you may want to skip wrapping that supplier with `CachingServiceInstanceListSupplier`.
 
 === Same instance preference for LoadBalancer

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/annotation/LoadBalancerClientConfiguration.java

@@ -43,6 +43,8 @@ import org.springframework.context.annotation.Primary;
 import org.springframework.core.annotation.Order;
 import org.springframework.core.env.Environment;
 import org.springframework.retry.support.RetryTemplate;
+import org.springframework.web.client.RestTemplate;
+import org.springframework.web.reactive.function.client.WebClient;
 
 /**
  * @author Spencer Gibb
@@ -90,7 +92,7 @@ public class LoadBalancerClientConfiguration {
 		}
 
 		@Bean
-		@ConditionalOnBean(ReactiveDiscoveryClient.class)
+		@ConditionalOnBean({ ReactiveDiscoveryClient.class, WebClient.Builder.class })
 		@ConditionalOnMissingBean
 		@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "health-check")
 		public ServiceInstanceListSupplier healthCheckDiscoveryClientServiceInstanceListSupplier(
@@ -148,12 +150,12 @@ public class LoadBalancerClientConfiguration {
 		}
 
 		@Bean
-		@ConditionalOnBean(DiscoveryClient.class)
+		@ConditionalOnBean({ DiscoveryClient.class, RestTemplate.class })
 		@ConditionalOnMissingBean
 		@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "health-check")
 		public ServiceInstanceListSupplier healthCheckDiscoveryClientServiceInstanceListSupplier(
 				ConfigurableApplicationContext context) {
-			return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withHealthChecks()
+			return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withBlockingHealthChecks()
 					.build(context);
 		}
 

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/HealthCheckServiceInstanceListSupplier.java

@@ -19,6 +19,7 @@ package org.springframework.cloud.loadbalancer.core;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.function.BiFunction;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -31,14 +32,11 @@ import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.cloud.client.ServiceInstance;
 import org.springframework.cloud.client.loadbalancer.LoadBalancerProperties;
-import org.springframework.http.HttpStatus;
-import org.springframework.web.reactive.function.client.WebClient;
-import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * A {@link ServiceInstanceListSupplier} implementation that verifies whether the
- * instances are alive and only returns the healthy one, unless there are none. Uses
- * {@link WebClient} to ping the <code>health</code> endpoint of the instances.
+ * instances are alive and only returns the healthy one, unless there are none. Uses a
+ * user-provided function to ping the <code>health</code> endpoint of the instances.
  *
  * @author Olga Maciaszek-Sharma
  * @author Roman Matiushchenko
@@ -51,19 +49,20 @@ public class HealthCheckServiceInstanceListSupplier extends DelegatingServiceIns
 
 	private final LoadBalancerProperties.HealthCheck healthCheck;
 
-	private final WebClient webClient;
-
 	private final String defaultHealthCheckPath;
 
 	private final Flux<List<ServiceInstance>> aliveInstancesReplay;
 
 	private Disposable healthCheckDisposable;
 
+	private final BiFunction<ServiceInstance, String, Mono<Boolean>> aliveFunction;
+
 	public HealthCheckServiceInstanceListSupplier(ServiceInstanceListSupplier delegate,
-			LoadBalancerProperties.HealthCheck healthCheck, WebClient webClient) {
+			LoadBalancerProperties.HealthCheck healthCheck,
+			BiFunction<ServiceInstance, String, Mono<Boolean>> aliveFunction) {
 		super(delegate);
 		defaultHealthCheckPath = healthCheck.getPath().getOrDefault("default", "/actuator/health");
-		this.webClient = webClient;
+		this.aliveFunction = aliveFunction;
 		this.healthCheck = healthCheck;
 		Repeat<Object> aliveInstancesReplayRepeat = Repeat
 				.onlyIf(repeatContext -> this.healthCheck.getRefetchInstances())
@@ -129,10 +128,7 @@ public class HealthCheckServiceInstanceListSupplier extends DelegatingServiceIns
 	protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 		String healthCheckPropertyValue = healthCheck.getPath().get(serviceInstance.getServiceId());
 		String healthCheckPath = healthCheckPropertyValue != null ? healthCheckPropertyValue : defaultHealthCheckPath;
-		return webClient.get()
-				.uri(UriComponentsBuilder.fromUri(serviceInstance.getUri()).path(healthCheckPath).build().toUri())
-				.exchange().flatMap(clientResponse -> clientResponse.releaseBody()
-						.thenReturn(HttpStatus.OK.value() == clientResponse.rawStatusCode()));
+		return aliveFunction.apply(serviceInstance, healthCheckPath);
 	}
 
 	@Override

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/ServiceInstanceListSupplierBuilder.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.loadbalancer.core;
 
+import java.net.URI;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.BiFunction;
@@ -23,6 +24,7 @@ import java.util.function.Function;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import reactor.core.publisher.Mono;
 
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.cloud.client.discovery.DiscoveryClient;
@@ -31,8 +33,11 @@ import org.springframework.cloud.client.loadbalancer.LoadBalancerProperties;
 import org.springframework.cloud.loadbalancer.cache.LoadBalancerCacheManager;
 import org.springframework.cloud.loadbalancer.config.LoadBalancerZoneConfig;
 import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.http.HttpStatus;
 import org.springframework.util.Assert;
+import org.springframework.web.client.RestTemplate;
 import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * A Builder for creating a {@link ServiceInstanceListSupplier} hierarchy to be used in
@@ -110,7 +115,22 @@ public final class ServiceInstanceListSupplierBuilder {
 		DelegateCreator creator = (context, delegate) -> {
 			LoadBalancerProperties properties = context.getBean(LoadBalancerProperties.class);
 			WebClient.Builder webClient = context.getBean(WebClient.Builder.class);
-			return new HealthCheckServiceInstanceListSupplier(delegate, properties.getHealthCheck(), webClient.build());
+			return healthCheckServiceInstanceListSupplier(webClient.build(), delegate, properties);
+		};
+		this.creators.add(creator);
+		return this;
+	}
+
+	/**
+	 * Adds a {@link HealthCheckServiceInstanceListSupplier} that uses user-provided
+	 * {@link WebClient} instance to the {@link ServiceInstanceListSupplier} hierarchy.
+	 * @param webClient a user-provided {@link WebClient} instance
+	 * @return the {@link ServiceInstanceListSupplierBuilder} object
+	 */
+	public ServiceInstanceListSupplierBuilder withHealthChecks(WebClient webClient) {
+		DelegateCreator creator = (context, delegate) -> {
+			LoadBalancerProperties properties = context.getBean(LoadBalancerProperties.class);
+			return healthCheckServiceInstanceListSupplier(webClient, delegate, properties);
 		};
 		this.creators.add(creator);
 		return this;
@@ -130,14 +150,29 @@ public final class ServiceInstanceListSupplierBuilder {
 
 	/**
 	 * Adds a {@link HealthCheckServiceInstanceListSupplier} that uses user-provided
-	 * {@link WebClient} instance to the {@link ServiceInstanceListSupplier} hierarchy.
-	 * @param webClient a user-provided {@link WebClient} instance
+	 * {@link RestTemplate} instance to the {@link ServiceInstanceListSupplier} hierarchy.
 	 * @return the {@link ServiceInstanceListSupplierBuilder} object
 	 */
-	public ServiceInstanceListSupplierBuilder withHealthChecks(WebClient webClient) {
+	public ServiceInstanceListSupplierBuilder withBlockingHealthChecks() {
+		DelegateCreator creator = (context, delegate) -> {
+			RestTemplate restTemplate = context.getBean(RestTemplate.class);
+			LoadBalancerProperties properties = context.getBean(LoadBalancerProperties.class);
+			return blockingHealthCheckServiceInstanceListSupplier(restTemplate, delegate, properties);
+		};
+		this.creators.add(creator);
+		return this;
+	}
+
+	/**
+	 * Adds a {@link HealthCheckServiceInstanceListSupplier} that uses user-provided
+	 * {@link RestTemplate} instance to the {@link ServiceInstanceListSupplier} hierarchy.
+	 * @param restTemplate a user-provided {@link RestTemplate} instance
+	 * @return the {@link ServiceInstanceListSupplierBuilder} object
+	 */
+	public ServiceInstanceListSupplierBuilder withBlockingHealthChecks(RestTemplate restTemplate) {
 		DelegateCreator creator = (context, delegate) -> {
 			LoadBalancerProperties properties = context.getBean(LoadBalancerProperties.class);
-			return new HealthCheckServiceInstanceListSupplier(delegate, properties.getHealthCheck(), webClient);
+			return blockingHealthCheckServiceInstanceListSupplier(restTemplate, delegate, properties);
 		};
 		this.creators.add(creator);
 		return this;
@@ -225,6 +260,32 @@ public final class ServiceInstanceListSupplierBuilder {
 		return supplier;
 	}
 
+	private ServiceInstanceListSupplier healthCheckServiceInstanceListSupplier(WebClient webClient,
+			ServiceInstanceListSupplier delegate, LoadBalancerProperties properties) {
+		return new HealthCheckServiceInstanceListSupplier(delegate, properties.getHealthCheck(),
+				(serviceInstance, healthCheckPath) -> webClient.get()
+						.uri(UriComponentsBuilder.fromUri(serviceInstance.getUri()).path(healthCheckPath).build()
+								.toUri())
+						.exchange().flatMap(clientResponse -> clientResponse.releaseBody()
+								.thenReturn(HttpStatus.OK.value() == clientResponse.rawStatusCode())));
+	}
+
+	private ServiceInstanceListSupplier blockingHealthCheckServiceInstanceListSupplier(RestTemplate restTemplate,
+			ServiceInstanceListSupplier delegate, LoadBalancerProperties properties) {
+		return new HealthCheckServiceInstanceListSupplier(delegate, properties.getHealthCheck(),
+				(serviceInstance, healthCheckPath) -> Mono.defer(() -> {
+					URI uri = UriComponentsBuilder.fromUri(serviceInstance.getUri()).path(healthCheckPath).build()
+							.toUri();
+					try {
+						return Mono
+								.just(HttpStatus.OK.equals(restTemplate.getForEntity(uri, Void.class).getStatusCode()));
+					}
+					catch (Exception ignored) {
+						return Mono.just(false);
+					}
+				}));
+	}
+
 	/**
 	 * Allows creating a {@link ServiceInstanceListSupplier} instance based on provided
 	 * {@link ConfigurableApplicationContext}.

spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/annotation/LoadBalancerClientConfigurationTests.java

@@ -37,6 +37,7 @@ import org.springframework.cloud.loadbalancer.core.ZonePreferenceServiceInstance
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.retry.support.RetryTemplate;
+import org.springframework.web.client.RestTemplate;
 import org.springframework.web.reactive.function.client.WebClient;
 
 import static org.assertj.core.api.BDDAssertions.then;
@@ -170,6 +171,17 @@ class LoadBalancerClientConfigurationTests {
 
 	}
 
+	@Test
+	void shouldInstantiateBlockingHealthCheckServiceInstanceListSupplier() {
+		blockingDiscoveryClientRunner.withUserConfiguration(RestTemplateTestConfig.class)
+				.withPropertyValues("spring.cloud.loadbalancer.configurations=health-check").run(context -> {
+					ServiceInstanceListSupplier supplier = context.getBean(ServiceInstanceListSupplier.class);
+					then(supplier).isInstanceOf(HealthCheckServiceInstanceListSupplier.class);
+					then(((DelegatingServiceInstanceListSupplier) supplier).getDelegate())
+							.isInstanceOf(DiscoveryClientServiceInstanceListSupplier.class);
+				});
+	}
+
 	@Configuration
 	protected static class TestConfig {
 
@@ -181,4 +193,14 @@ class LoadBalancerClientConfigurationTests {
 
 	}
 
+	@Configuration
+	protected static class RestTemplateTestConfig {
+
+		@Bean
+		RestTemplate restTemplate() {
+			return new RestTemplate();
+		}
+
+	}
+
 }

spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/core/CachingServiceInstanceListSupplierTests.java

@@ -41,6 +41,7 @@ import org.springframework.web.reactive.function.client.WebClient;
 
 import static java.time.Duration.ofMillis;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
+import static org.springframework.cloud.loadbalancer.core.ServiceInstanceListSuppliersTestUtils.healthCheckFunction;
 
 /**
  * Tests for {@link CachingServiceInstanceListSupplier}.
@@ -140,7 +141,7 @@ class CachingServiceInstanceListSupplierTests {
 
 			TestHealthCheckServiceInstanceListSupplier(ServiceInstanceListSupplier delegate,
 					LoadBalancerProperties.HealthCheck healthCheck, WebClient webClient) {
-				super(delegate, healthCheck, webClient);
+				super(delegate, healthCheck, healthCheckFunction(webClient));
 			}
 
 			@Override

spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/core/HealthCheckServiceInstanceListSupplierTests.java

@@ -46,11 +46,13 @@ import org.springframework.context.annotation.Configuration;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.client.RestTemplate;
 import org.springframework.web.reactive.function.client.WebClient;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
+import static org.springframework.cloud.loadbalancer.core.ServiceInstanceListSuppliersTestUtils.healthCheckFunction;
 
 /**
  * Tests for {@link HealthCheckServiceInstanceListSupplier}.
@@ -72,6 +74,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 
 	private final WebClient webClient = WebClient.create();
 
+	private final RestTemplate restTemplate = new RestTemplate();
+
 	private LoadBalancerProperties.HealthCheck healthCheck;
 
 	private HealthCheckServiceInstanceListSupplier listSupplier;
@@ -97,7 +101,24 @@ class HealthCheckServiceInstanceListSupplierTests {
 		ServiceInstance serviceInstance = new DefaultServiceInstance("ignored-service-1", serviceId, "127.0.0.1", port,
 				false);
 		listSupplier = new HealthCheckServiceInstanceListSupplier(
-				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck, webClient);
+				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck,
+				healthCheckFunction(webClient));
+
+		boolean alive = listSupplier.isAlive(serviceInstance).block();
+
+		assertThat(alive).isTrue();
+	}
+
+	@SuppressWarnings("ConstantConditions")
+	@Test
+	void shouldCheckInstanceWithProvidedHealthCheckPathWithRestTemplate() {
+		String serviceId = "ignored-service";
+		healthCheck.getPath().put("ignored-service", "/health");
+		ServiceInstance serviceInstance = new DefaultServiceInstance("ignored-service-1", serviceId, "127.0.0.1", port,
+				false);
+		listSupplier = new HealthCheckServiceInstanceListSupplier(
+				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck,
+				healthCheckFunction(restTemplate));
 
 		boolean alive = listSupplier.isAlive(serviceInstance).block();
 
@@ -111,7 +132,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 		ServiceInstance serviceInstance = new DefaultServiceInstance("ignored-service-1", serviceId, "127.0.0.1", port,
 				false);
 		listSupplier = new HealthCheckServiceInstanceListSupplier(
-				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck, webClient);
+				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck,
+				healthCheckFunction(webClient));
 
 		boolean alive = listSupplier.isAlive(serviceInstance).block();
 
@@ -126,7 +148,24 @@ class HealthCheckServiceInstanceListSupplierTests {
 				false);
 		healthCheck.getPath().put(serviceId, "/test");
 		listSupplier = new HealthCheckServiceInstanceListSupplier(
-				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck, webClient);
+				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck,
+				healthCheckFunction(webClient));
+
+		boolean alive = listSupplier.isAlive(serviceInstance).block();
+
+		assertThat(alive).isFalse();
+	}
+
+	@SuppressWarnings("ConstantConditions")
+	@Test
+	void shouldReturnFalseIfEndpointNotFoundWithRestTemplate() {
+		String serviceId = "ignored-service";
+		ServiceInstance serviceInstance = new DefaultServiceInstance("ignored-service-1", serviceId, "127.0.0.1", port,
+				false);
+		healthCheck.getPath().put(serviceId, "/test");
+		listSupplier = new HealthCheckServiceInstanceListSupplier(
+				ServiceInstanceListSuppliers.from(serviceId, serviceInstance), healthCheck,
+				healthCheckFunction(restTemplate));
 
 		boolean alive = listSupplier.isAlive(serviceInstance).block();
 
@@ -151,7 +190,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			Mockito.doReturn(Mono.just(true)).when(mock).isAlive(serviceInstance1);
 			Mockito.doReturn(Mono.just(false)).when(mock).isAlive(serviceInstance2);
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return mock.isAlive(serviceInstance);
@@ -180,7 +220,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			Mockito.doReturn(Mono.just(true)).when(mock).isAlive(serviceInstance1);
 			Mockito.doReturn(Mono.just(true)).when(mock).isAlive(serviceInstance2);
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return mock.isAlive(serviceInstance);
@@ -210,7 +251,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			Mockito.doReturn(Mono.just(true)).when(mock).isAlive(serviceInstance1);
 			Mockito.doReturn(Mono.error(new RuntimeException("boom"))).when(mock).isAlive(serviceInstance2);
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return mock.isAlive(serviceInstance);
@@ -234,7 +276,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			ServiceInstanceListSupplier delegate = mock(ServiceInstanceListSupplier.class);
 			Mockito.when(delegate.getServiceId()).thenReturn(SERVICE_ID);
 			Mockito.when(delegate.get()).thenReturn(Flux.just(Lists.list(serviceInstance1, serviceInstance2)));
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					if (serviceInstance == serviceInstance1) {
@@ -261,7 +304,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			ServiceInstanceListSupplier delegate = mock(ServiceInstanceListSupplier.class);
 			Mockito.when(delegate.getServiceId()).thenReturn(SERVICE_ID);
 			Mockito.when(delegate.get()).thenReturn(Flux.just(Lists.list(serviceInstance1)));
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return Mono.just(true);
@@ -292,7 +336,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			Mockito.doReturn(Mono.just(false), Mono.just(true)).when(mock).isAlive(serviceInstance1);
 			Mockito.doReturn(Mono.error(new RuntimeException("boom"))).when(mock).isAlive(serviceInstance2);
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return mock.isAlive(serviceInstance);
@@ -320,7 +365,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			HealthCheckServiceInstanceListSupplier mock = mock(HealthCheckServiceInstanceListSupplier.class);
 			Mockito.when(mock.isAlive(serviceInstance1)).thenReturn(Mono.never(), Mono.just(true));
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return mock.isAlive(serviceInstance);
@@ -350,7 +396,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 							.delayElements(healthCheck.getInterval().dividedBy(2)));
 			Mockito.when(delegate.get()).thenReturn(instances);
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return Mono.just(true);
@@ -380,7 +427,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			ServiceInstanceListSupplier delegate = mock(ServiceInstanceListSupplier.class);
 			when(delegate.get()).thenReturn(Flux.just(Collections.singletonList(serviceInstance1)))
 					.thenReturn(Flux.just(Collections.singletonList(serviceInstance2)));
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return Mono.just(true);
@@ -405,7 +453,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 			Mockito.when(delegate.getServiceId()).thenReturn(SERVICE_ID);
 			Mockito.when(delegate.get()).thenReturn(Flux.just(Lists.list(serviceInstance1)));
 
-			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient) {
+			listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+					healthCheckFunction(webClient)) {
 				@Override
 				protected Mono<Boolean> isAlive(ServiceInstance serviceInstance) {
 					return Mono.just(true);
@@ -435,7 +484,8 @@ class HealthCheckServiceInstanceListSupplierTests {
 		Mockito.when(delegate.get()).thenReturn(Flux.<List<ServiceInstance>>never()
 				.doOnSubscribe(subscription -> subscribed.set(true)).doOnCancel(instancesCanceled::incrementAndGet));
 
-		listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck, webClient);
+		listSupplier = new HealthCheckServiceInstanceListSupplier(delegate, healthCheck,
+				healthCheckFunction(webClient));
 
 		listSupplier.afterPropertiesSet();
 

spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/core/ServiceInstanceListSuppliersTestUtils.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2013-2020 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 org.springframework.cloud.loadbalancer.core;
+
+import java.net.URI;
+import java.util.function.BiFunction;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.client.RestTemplate;
+import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.util.UriComponentsBuilder;
+
+/**
+ * A utility class for {@link ServiceInstanceListSupplier} tests.
+ *
+ * @author Olga Maciaszek-Sharma
+ * @since 3.0.0
+ */
+final class ServiceInstanceListSuppliersTestUtils {
+
+	private ServiceInstanceListSuppliersTestUtils() {
+		throw new UnsupportedOperationException("Cannot instantiate utility class");
+	}
+
+	static BiFunction<ServiceInstance, String, Mono<Boolean>> healthCheckFunction(WebClient webClient) {
+		return (serviceInstance, healthCheckPath) -> webClient.get()
+				.uri(UriComponentsBuilder.fromUri(serviceInstance.getUri()).path(healthCheckPath).build().toUri())
+				.exchange().flatMap(clientResponse -> clientResponse.releaseBody()
+						.thenReturn(HttpStatus.OK.value() == clientResponse.rawStatusCode()));
+	}
+
+	static BiFunction<ServiceInstance, String, Mono<Boolean>> healthCheckFunction(RestTemplate restTemplate) {
+		return (serviceInstance, healthCheckPath) -> Mono.defer(() -> {
+			URI uri = UriComponentsBuilder.fromUri(serviceInstance.getUri()).path(healthCheckPath).build().toUri();
+			try {
+				return Mono.just(HttpStatus.OK.equals(restTemplate.getForEntity(uri, Void.class).getStatusCode()));
+			}
+			catch (Exception ignored) {
+				return Mono.just(false);
+			}
+		});
+	}
+
+}