Add Reactive retries for SC LoadBalancer (#847)

* Implement retry logic.

* Fix retrying on next instance when RetryExhausted in same instance.

* Fix retrying on next instance when RetryExhausted in same instance.

* Fix retrying on next instance when RetryExhausted in same instance.

* Move duplicated methods to utility class. Fix checkstyle.

* Fix test.

* Add more tests.

* Fix test.

* Add autoConfiguration.

* Refactor and add javadocs.

* Add javadocs.

* Use RetryAwareServiceInstanceListSupplier with reactive retries.

* Update properties.

* Fix the docs.

* Rename utility class.

* Verify interactions in order.

docs/src/main/asciidoc/_configprops.adoc

@@ -32,6 +32,10 @@
 |spring.cloud.loadbalancer.health-check.path |  | 
 |spring.cloud.loadbalancer.hint |  | Allows setting the value of <code>hint</code> that is passed on to the LoadBalancer request and can subsequently be used in {@link ReactiveLoadBalancer} implementations.
 |spring.cloud.loadbalancer.retry.avoid-previous-instance | true | Enables wrapping ServiceInstanceListSupplier beans with `RetryAwareServiceInstanceListSupplier` if Spring-Retry is in the classpath.
+|spring.cloud.loadbalancer.retry.backoff.enabled | false | Indicates whether Reactor Retry backoffs should be applied.
+|spring.cloud.loadbalancer.retry.backoff.jitter | 0.5 | Used to set {@link RetryBackoffSpec#jitter}.
+|spring.cloud.loadbalancer.retry.backoff.max-backoff |  | Used to set {@link RetryBackoffSpec#maxBackoff}.
+|spring.cloud.loadbalancer.retry.backoff.min-backoff | 5ms | Used to set {@link RetryBackoffSpec#minBackoff}.
 |spring.cloud.loadbalancer.retry.enabled | true | 
 |spring.cloud.loadbalancer.retry.max-retries-on-next-service-instance | 1 | Number of retries to be executed on the next <code>ServiceInstance</code>. A <code>ServiceInstance</code> is chosen before each retry call.
 |spring.cloud.loadbalancer.retry.max-retries-on-same-service-instance | 0 | Number of retries to be executed on the same <code>ServiceInstance</code>.

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

@@ -437,11 +437,13 @@ Then, `ReactiveLoadBalancer` is used underneath.
 
 A load-balanced `RestTemplate` can be configured to retry failed requests.
 By default, this logic is disabled.
-You can enable it by adding link:https://github.com/spring-projects/spring-retry[Spring Retry] to your application's classpath.
+For the non-reactive version (with `RestTemplate`), you can enable it by adding link:https://github.com/spring-projects/spring-retry[Spring Retry] to your application's classpath. For the reactive version (with `WebTestClient), you need to set `spring.cloud.loadbalancer.retry.enabled=false`.
 
-If you would like to disable the retry logic with Spring Retry on the classpath, you can set `spring.cloud.loadbalancer.retry.enabled=false`.
+If you would like to disable the retry logic with Spring Retry or Reactive Retry on the classpath, you can set `spring.cloud.loadbalancer.retry.enabled=false`.
 
-If you would like to implement a `BackOffPolicy` in your retries, you need to create a bean of type `LoadBalancedRetryFactory` and override the `createBackOffPolicy()` method.
+For the non-reactive implementation, if you would like to implement a `BackOffPolicy` in your retries, you need to create a bean of type `LoadBalancedRetryFactory` and override the `createBackOffPolicy()` method.
+
+For the reactive implementation, you just need to enable it by setting `spring.cloud.loadbalancer.retry.backoff.enabled` to `false`.
 
 You can set:
 
@@ -449,6 +451,13 @@ You can set:
 - `spring.cloud.loadbalancer.retry.maxRetriesOnNextServiceInstance` - indicates how many times a request should be retried a newly selected `ServiceInstance`
 - `spring.cloud.loadbalancer.retry.retryableStatusCodes` - the status codes on which to always retry a failed request.
 
+For the reactive implementation, you can additionally set:
+ - `spring.cloud.loadbalancer.retry.backoff.minBackoff` - Sets the minimum backoff duration (by default, 5 milliseconds)
+ - `spring.cloud.loadbalancer.retry.backoff.maxBackoff` - Sets the maximum backoff duration (by default, max long value of milliseconds)
+ - `spring.cloud.loadbalancer.retry.backoff.jitter` - Sets the jitter used for calculationg the actual backoff duration for each call (by default, 0.5).
+
+For the reactive implementation, you can also implement your own `LoadBalancerRetryPolicy` to have more detailed control over the load-balanced call retries.
+
 NOTE: For load-balanced retries, by default, we wrap the `ServiceInstanceListSupplier` bean with `RetryAwareServiceInstanceListSupplier` to select a different instance from the one previously chosen, if available. You can disable this behavior by setting the value of `spring.cloud.loadbalancer.retry.avoidPreviousInstance` to `false`.
 
 ====