Allow disabling load-balancing with property. (#940)

docs/src/main/asciidoc/_configprops.adoc

@@ -30,6 +30,7 @@
 |spring.cloud.loadbalancer.cache.enabled | `true` | Enables Spring Cloud LoadBalancer caching mechanism.
 |spring.cloud.loadbalancer.cache.ttl | `35s` | Time To Live - time counted from writing of the record, after which cache entries are expired, expressed as a {@link Duration}. The property {@link String} has to be in keeping with the appropriate syntax as specified in Spring Boot <code>StringToDurationConverter</code>. @see <a href= "https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/convert/StringToDurationConverter.java">StringToDurationConverter.java</a>
 |spring.cloud.loadbalancer.configurations | `default` | Enables a predefined LoadBalancer configuration.
+|spring.cloud.loadbalancer.enabled | `true` | Enables Spring Cloud LoadBalancer.
 |spring.cloud.loadbalancer.health-check.initial-delay | `0` | Initial delay value for the HealthCheck scheduler.
 |spring.cloud.loadbalancer.health-check.interval | `25s` | Interval for rerunning the HealthCheck scheduler.
 |spring.cloud.loadbalancer.health-check.path |  | 

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

@@ -845,6 +845,8 @@ have been provided for it. In order to get instances to select from reactive `Se
 is used. Currently we support a service-discovery-based implementation of `ServiceInstanceListSupplier`
 that retrieves available instances from Service Discovery using a <<discovery-client, Discovery Client>> available in the classpath.
 
+TIP: It is possible to disable Spring Cloud LoadBalancer by setting the value of `spring.cloud.loadbalancer.enabled` to `false`.
+
 === Switching between the load-balancing algorithms
 
 The `ReactiveLoadBalancer` implementation that is used by default is `RoundRobinLoadBalancer`. To switch to a different implementation, either for selected services or all of them, you can use the <<custom-loadbalancer-configuration, custom LoadBalancer configurations mechanism>>.

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

@@ -22,6 +22,7 @@ import java.util.List;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.cloud.client.loadbalancer.LoadBalancerProperties;
 import org.springframework.cloud.client.loadbalancer.reactive.LoadBalancerBeanPostProcessorAutoConfiguration;
@@ -42,6 +43,7 @@ import org.springframework.core.env.Environment;
 @EnableConfigurationProperties(LoadBalancerProperties.class)
 @AutoConfigureBefore({ ReactorLoadBalancerClientAutoConfiguration.class,
 		LoadBalancerBeanPostProcessorAutoConfiguration.class })
+@ConditionalOnProperty(value = "spring.cloud.loadbalancer.enabled", havingValue = "true", matchIfMissing = true)
 public class LoadBalancerAutoConfiguration {
 
 	private final ObjectProvider<List<LoadBalancerClientSpecification>> configurations;

spring-cloud-loadbalancer/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -33,6 +33,12 @@
 			"name": "spring.cloud.loadbalancer.configurations",
 			"description": "Enables a predefined LoadBalancer configuration.",
 			"type": "java.lang.String"
+		},
+		{
+			"defaultValue": "true",
+			"name": "spring.cloud.loadbalancer.enabled",
+			"description": "Enables Spring Cloud LoadBalancer.",
+			"type": "java.lang.Boolean"
 		}
 	]
 }