Fix execution thread for blocking and adjusts timing

* Fix execution thread for blocking DiscoveryClientServiceInstanceListSupplier.

* Desynchronise HealthCheck and Cache. Add info about using HealthCheck without Cache to docs.

See gh-760

Author: OlgaMaciaszek

docs/src/main/asciidoc/_configprops.adoc

@@ -29,9 +29,9 @@
 |spring.cloud.inetutils.use-only-site-local-interfaces | false | Whether to use only interfaces with site local addresses. See {@link InetAddress#isSiteLocalAddress()} for more details.
 |spring.cloud.loadbalancer.cache.caffeine.spec |  | The spec to use to create caches. See CaffeineSpec for more details on the spec format.
 |spring.cloud.loadbalancer.cache.capacity | 256 | Initial cache capacity expressed as int.
-|spring.cloud.loadbalancer.cache.ttl | 30s | 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.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.health-check.initial-delay | 0 | Initial delay value for the HealthCheck scheduler.
-|spring.cloud.loadbalancer.health-check.interval | 30s | Interval for rerunning the HealthCheck scheduler.
+|spring.cloud.loadbalancer.health-check.interval | 25s | Interval for rerunning the HealthCheck scheduler.
 |spring.cloud.loadbalancer.health-check.path |  | 
 |spring.cloud.loadbalancer.retry.enabled | true | 
 |spring.cloud.loadbalancer.ribbon.enabled | true | Causes `RibbonLoadBalancerClient` to be used by default.

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

@@ -882,7 +882,7 @@ You can set your own `ttl` value (the time after write after which entries shoul
 as the value of the `spring.cloud.loadbalancer.cache.ttl` property.
 You can also set your own LoadBalancer cache initial capacity by setting the value of the `spring.cloud.loadbalancer.cache.capacity` property.
 
-The default setup includes `ttl` set to 30 seconds and the default `initialCapacity` is `256`.
+The default setup includes `ttl` set to 35 seconds and the default `initialCapacity` is `256`.
 
 You can also altogether disable loadBalancer caching by setting the value of `spring.cloud.loadbalancer.cache.enabled`
 to `false`.
@@ -951,7 +951,7 @@ We suggest passing a `DiscoveryClientServiceInstanceListSupplier` delegate in th
 
 You could use this sample configuration to set it up:
 
-[[zoned-based-custom-loadbalancer-configuration]]
+[[health-check-based-custom-loadbalancer-configuration]]
 [source,java,indent=0]
 ----
 public class CustomLoadBalancerConfiguration {
@@ -962,12 +962,13 @@ public class CustomLoadBalancerConfiguration {
 		return ServiceInstanceListSupplier.builder()
 					.withDiscoveryClient()
 					.withHealthChecks()
-					.withCaching()
 					.build(context);
 	    }
 	}
 ----
 
+NOTE:: `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`.
+
 TIP:: In order to make working on your own LoadBalancer configuration easier, we have added a `builder()` method to the `ServiceInstanceListSupplier` class.
 
 TIP:: You can also use our alternative predefined configurations in place of the default ones by setting the value of `spring.cloud.loadbalancer.configurations` property to `zone-preference` to use `ZonePreferenceServiceInstanceListSupplier` with caching or to `health-check` to use `HealthCheckServiceInstanceListSupplier` with caching.

spring-cloud-commons/src/main/java/org/springframework/cloud/client/loadbalancer/reactive/LoadBalancerProperties.java

@@ -54,7 +54,7 @@ public static class HealthCheck {
 		/**
 		 * Interval for rerunning the HealthCheck scheduler.
 		 */
-		private Duration interval = Duration.ofSeconds(30);
+		private Duration interval = Duration.ofSeconds(25);
 
 		private Map<String, String> path = new LinkedCaseInsensitiveMap<>();
 

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/config/SimpleBootstrapPropertySource.java

@@ -22,6 +22,7 @@
 
 /**
  * Simple, non-enumerable PropertySource wrapper.
+ *
  * @author Ryan Baxter
  */
 public class SimpleBootstrapPropertySource<T> extends PropertySource<T> {

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/cache/LoadBalancerCacheProperties.java

@@ -39,7 +39,7 @@ public class LoadBalancerCacheProperties {
 	 * @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>
 	 */
-	private Duration ttl = Duration.ofSeconds(30);
+	private Duration ttl = Duration.ofSeconds(35);
 
 	/**
 	 * Initial cache capacity expressed as int.

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

@@ -47,8 +47,8 @@ public DiscoveryClientServiceInstanceListSupplier(DiscoveryClient delegate,
 			Environment environment) {
 		this.serviceId = environment.getProperty(PROPERTY_NAME);
 		this.serviceInstances = Flux
-				.defer(() -> Flux.fromIterable(delegate.getInstances(serviceId))
-						.collectList().flux().subscribeOn(Schedulers.boundedElastic()));
+				.defer(() -> Flux.just(delegate.getInstances(serviceId)))
+				.subscribeOn(Schedulers.boundedElastic());
 	}
 
 	public DiscoveryClientServiceInstanceListSupplier(ReactiveDiscoveryClient delegate,

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

@@ -109,21 +109,18 @@ void shouldReturnRetrievedInstancesBlockingClient() {
 
 	@Test
 	void shouldUpdateReturnRetrievedInstancesBlockingClient() {
-		when(discoveryClient.getInstances(SERVICE_ID)).thenReturn(
-				Lists.list(instance("1host", false), instance("2host-secure", true)));
-		supplier = new DiscoveryClientServiceInstanceListSupplier(discoveryClient,
-				environment);
-
-		StepVerifier.withVirtualTime(() -> supplier.get()).expectSubscription()
-				.expectNext(Lists.list(instance("1host", false),
-						instance("2host-secure", true)))
-				.thenCancel().verify();
-
-		when(discoveryClient.getInstances(SERVICE_ID))
-				.thenReturn(Lists.list(instance("1host", false),
-						instance("2host-secure", true), instance("3host", false)));
+		StepVerifier.withVirtualTime(() -> {
+			when(discoveryClient.getInstances(SERVICE_ID)).thenReturn(
+					Lists.list(instance("1host", false), instance("2host-secure", true)));
+			supplier = new DiscoveryClientServiceInstanceListSupplier(discoveryClient,
+					environment);
+			supplier.get();
 
-		StepVerifier.withVirtualTime(() -> supplier.get()).expectSubscription()
+			when(discoveryClient.getInstances(SERVICE_ID))
+					.thenReturn(Lists.list(instance("1host", false),
+							instance("2host-secure", true), instance("3host", false)));
+			return supplier.get();
+		}).expectSubscription()
 				.expectNext(Lists.list(instance("1host", false),
 						instance("2host-secure", true), instance("3host", false)))
 				.thenCancel().verify();