feat: Multi-AZ Failover LoadBalancing

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

@@ -118,6 +118,16 @@ public ServiceInstanceListSupplier healthCheckDiscoveryClientServiceInstanceList
 			return ServiceInstanceListSupplier.builder().withDiscoveryClient().withHealthChecks().build(context);
 		}
 
+		@Bean
+		@ConditionalOnBean(ReactiveDiscoveryClient.class)
+		@ConditionalOnMissingBean
+		@Conditional(MultiAZFailoverConfigurationCondition.class)
+		public ServiceInstanceListSupplier multiAZFailoverDiscoveryClientServiceInstanceListSupplier(
+				ConfigurableApplicationContext context) {
+			return ServiceInstanceListSupplier.builder().withDiscoveryClient().withMultiAZFailover().withCaching()
+					.build(context);
+		}
+
 		@Bean
 		@ConditionalOnBean(ReactiveDiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -221,6 +231,16 @@ public ServiceInstanceListSupplier healthCheckRestClientDiscoveryClientServiceIn
 				.build(context);
 		}
 
+		@Bean
+		@ConditionalOnBean(DiscoveryClient.class)
+		@ConditionalOnMissingBean
+		@Conditional(MultiAZFailoverConfigurationCondition.class)
+		public ServiceInstanceListSupplier multiAZFailoverServiceInstanceListSupplier(
+				ConfigurableApplicationContext context) {
+			return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withMultiAZFailover()
+					.withCaching().build(context);
+		}
+
 		@Bean
 		@ConditionalOnBean(DiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -386,6 +406,16 @@ public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata)
 
 	}
 
+	static class MultiAZFailoverConfigurationCondition implements Condition {
+
+		@Override
+		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+			return LoadBalancerEnvironmentPropertyUtils.equalToForClientOrDefault(context.getEnvironment(),
+					"configurations", "multi-az-failover");
+		}
+
+	}
+
 	static class RequestBasedStickySessionConfigurationCondition implements Condition {
 
 		@Override

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/LoadBalancerAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.loadbalancer.config;
 
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -37,23 +38,27 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.env.Environment;
+import org.springframework.util.StringUtils;
 
 /**
  * @author Spencer Gibb
  * @author Olga Maciaszek-Sharma
+ * @author Jiwon Jeon
  */
 @Configuration(proxyBeanMethods = false)
 @LoadBalancerClients
-@EnableConfigurationProperties({ LoadBalancerClientsProperties.class, LoadBalancerEagerLoadProperties.class })
-@AutoConfigureBefore({ ReactorLoadBalancerClientAutoConfiguration.class,
-		LoadBalancerBeanPostProcessorAutoConfiguration.class })
+@EnableConfigurationProperties({LoadBalancerClientsProperties.class, LoadBalancerEagerLoadProperties.class})
+@AutoConfigureBefore({ReactorLoadBalancerClientAutoConfiguration.class,
+		LoadBalancerBeanPostProcessorAutoConfiguration.class})
 @ConditionalOnProperty(value = "spring.cloud.loadbalancer.enabled", havingValue = "true", matchIfMissing = true)
 public class LoadBalancerAutoConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean
 	public LoadBalancerZoneConfig zoneConfig(Environment environment) {
-		return new LoadBalancerZoneConfig(environment.getProperty("spring.cloud.loadbalancer.zone"));
+		return new LoadBalancerZoneConfig(environment.getProperty("spring.cloud.loadbalancer.zone"),
+				Arrays.stream(StringUtils.commaDelimitedListToStringArray(environment.getProperty("spring.cloud.loadbalancer.secondary-zones", "")))
+						.toList());
 	}
 
 	@ConditionalOnMissingBean

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/LoadBalancerCacheDataManagerConfiguration.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2012-2023 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.config;
+
+import com.github.benmanes.caffeine.cache.Caffeine;
+
+import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.AutoConfigureBefore;
+import org.springframework.boot.autoconfigure.condition.AnyNestedCondition;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.cache.caffeine.CaffeineCacheManager;
+import org.springframework.cloud.loadbalancer.cache.LoadBalancerCacheManager;
+import org.springframework.cloud.loadbalancer.core.LoadBalancerCacheDataManager;
+import org.springframework.cloud.loadbalancer.core.MultiAZFailoverLoadBalancerCacheDataManager;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Conditional;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.DependsOn;
+
+/**
+ * An AutoConfiguration that provides a {@link LoadBalancerCacheDataManager} bean for
+ * adding ServiceInstance into a cache.
+ *
+ * @author Jiwon Jeon
+ */
+@Configuration(proxyBeanMethods = false)
+@AutoConfigureAfter(LoadBalancerCacheAutoConfiguration.class)
+@AutoConfigureBefore(LoadBalancerLifecycleConfiguration.class)
+public class LoadBalancerCacheDataManagerConfiguration {
+
+	@Bean
+	@DependsOn("caffeineLoadBalancerCacheManager")
+	@ConditionalOnClass({ Caffeine.class, CaffeineCacheManager.class })
+	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "multi-az-failover")
+	LoadBalancerCacheDataManager multiAZFailoverCaffeineLoadBalancerCacheDataManager(ApplicationContext context) {
+		return new MultiAZFailoverLoadBalancerCacheDataManager(
+				context.getBean("caffeineLoadBalancerCacheManager", LoadBalancerCacheManager.class));
+	}
+
+	@Bean
+	@DependsOn("defaultLoadBalancerCacheManager")
+	@Conditional(OnCaffeineCacheMissingCondition.class)
+	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "multi-az-failover")
+	LoadBalancerCacheDataManager multiAZFailoverDefaultLoadBalancerCacheDataManager(ApplicationContext context) {
+		return new MultiAZFailoverLoadBalancerCacheDataManager(
+				context.getBean("defaultLoadBalancerCacheManager", LoadBalancerCacheManager.class));
+	}
+
+	static final class OnCaffeineCacheMissingCondition extends AnyNestedCondition {
+
+		private OnCaffeineCacheMissingCondition() {
+			super(ConfigurationPhase.REGISTER_BEAN);
+		}
+
+		@ConditionalOnMissingClass("com.github.benmanes.caffeine.cache.Caffeine")
+		static class CaffeineClassMissing {
+
+		}
+
+		@ConditionalOnMissingClass("org.springframework.cache.caffeine.CaffeineCacheManager")
+		static class CaffeineCacheManagerClassMissing {
+
+		}
+
+	}
+
+}

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/LoadBalancerLifecycleConfiguration.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2012-2023 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.config;
+
+import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.cloud.client.loadbalancer.LoadBalancerLifecycle;
+import org.springframework.cloud.loadbalancer.core.LoadBalancerCacheDataManager;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * An AutoConfiguration that provides {@link LoadBalancerLifecycle} bean defining
+ * behaviors before and after load-balancing.
+ *
+ * @author Jiwon Jeon
+ */
+@Configuration(proxyBeanMethods = false)
+@AutoConfigureAfter({ LoadBalancerCacheAutoConfiguration.class, LoadBalancerCacheDataManagerConfiguration.class })
+public class LoadBalancerLifecycleConfiguration {
+
+	@Bean
+	@ConditionalOnBean(LoadBalancerCacheDataManager.class)
+	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "multi-az-failover")
+	LoadBalancerLifecycle multiAZFailoverLoadBalancerLifecycle(LoadBalancerCacheDataManager cacheDataManager) {
+		return new MultiAZFailoverLoadBalancerLifecycle(cacheDataManager);
+	}
+
+}

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/LoadBalancerZoneConfig.java

@@ -16,8 +16,12 @@
 
 package org.springframework.cloud.loadbalancer.config;
 
+import java.util.Collections;
+import java.util.List;
+
 /**
  * @author Olga Maciaszek-Sharma
+ * @author Jiwon Jeon
  */
 public class LoadBalancerZoneConfig {
 
@@ -27,8 +31,15 @@ public class LoadBalancerZoneConfig {
 	 */
 	private String zone;
 
+	private List<String> secondaryZones;
+
 	public LoadBalancerZoneConfig(String zone) {
-		this.zone = zone;
+		this(zone, Collections.EMPTY_LIST);
+	}
+
+	public LoadBalancerZoneConfig(String primaryZone, List<String> secondaryZones) {
+		this.zone = primaryZone;
+		this.secondaryZones = secondaryZones;
 	}
 
 	public String getZone() {
@@ -39,4 +50,12 @@ public void setZone(String zone) {
 		this.zone = zone;
 	}
 
+	public List<String> getSecondaryZones() {
+		return secondaryZones;
+	}
+
+	public void setSecondaryZones(List<String> secondaryZones) {
+		this.secondaryZones = secondaryZones;
+	}
+
 }

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/MultiAZFailoverLoadBalancerLifecycle.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2012-2023 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.config;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.cloud.client.loadbalancer.CompletionContext;
+import org.springframework.cloud.client.loadbalancer.LoadBalancerLifecycle;
+import org.springframework.cloud.client.loadbalancer.Request;
+import org.springframework.cloud.client.loadbalancer.Response;
+import org.springframework.cloud.client.loadbalancer.ResponseData;
+import org.springframework.cloud.loadbalancer.core.LoadBalancerCacheDataManager;
+import org.springframework.web.reactive.result.view.RequestContext;
+
+/**
+ * A LoadBalancerLifecycle implementation that defines behaviors before and after
+ * load-balancing, considering Multi-AZ failover.
+ *
+ * @author Jiwon Jeon
+ */
+public class MultiAZFailoverLoadBalancerLifecycle
+		implements LoadBalancerLifecycle<RequestContext, ResponseData, ServiceInstance> {
+
+	private static final Log LOG = LogFactory.getLog(MultiAZFailoverLoadBalancerLifecycle.class);
+
+	private final LoadBalancerCacheDataManager cacheDataManager;
+
+	public MultiAZFailoverLoadBalancerLifecycle(LoadBalancerCacheDataManager cacheDataManager) {
+		this.cacheDataManager = cacheDataManager;
+	}
+
+	@Override
+	public boolean supports(Class requestContextClass, Class responseClass, Class serverTypeClass) {
+		return RequestContext.class.isAssignableFrom(requestContextClass)
+				&& ResponseData.class.isAssignableFrom(responseClass)
+				&& ServiceInstance.class.isAssignableFrom(serverTypeClass);
+	}
+
+	@Override
+	public void onStart(Request<RequestContext> request) {
+	}
+
+	@Override
+	public void onStartRequest(Request<RequestContext> request, Response<ServiceInstance> lbResponse) {
+	}
+
+	@Override
+	public void onComplete(CompletionContext<ResponseData, ServiceInstance, RequestContext> completionContext) {
+		final CompletionContext.Status status = completionContext.status();
+		final ServiceInstance instance = completionContext.getLoadBalancerResponse().getServer();
+		final ResponseData clientResponse = completionContext.getClientResponse();
+
+		if (CompletionContext.Status.DISCARD.equals(status)) {
+			if (LOG.isWarnEnabled()) {
+				LOG.warn("Any instance selected. Cache will be evicted...");
+			}
+
+			cacheDataManager.clear();
+		}
+		else if (CompletionContext.Status.FAILED.equals(status)
+				&& (clientResponse == null || clientResponse.getHttpStatus().is5xxServerError())) {
+			if (LOG.isErrorEnabled()) {
+				LOG.error(String.format("Requesting to [%s] failed", instance));
+			}
+
+			cacheDataManager.putInstance(instance);
+		}
+	}
+
+}

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

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2012-2023 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 org.springframework.cache.Cache;
+import org.springframework.cloud.client.ServiceInstance;
+import org.springframework.cloud.loadbalancer.cache.LoadBalancerCacheManager;
+
+/**
+ * An interface allows adding ServiceInstance into cache through
+ * {@link LoadBalancerCacheManager}.
+ *
+ * @author Jiwon Jeon
+ */
+public interface LoadBalancerCacheDataManager {
+
+	Cache getCache();
+
+	void clear();
+
+	<T> T getInstance(String key, Class<T> classType);
+
+	void putInstance(ServiceInstance instance);
+
+}