Moving common spring-cloud-circuitbreaker code to commons

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

@@ -0,0 +1,82 @@
+== Introduction
+
+Spring Cloud Circuit breaker provides an abstraction across different circuit breaker implementations.
+It provides a consistent API to use in your applications allowing you the developer to choose the circuit breaker implementation that best fits your needs for your app.
+
+=== Supported Implementations
+
+* https://github.com/Netflix/Hystrix[Netfix Hystrix]
+* https://github.com/resilience4j/resilience4j[Resilience4J]
+* https://github.com/alibaba/Sentinel[Sentinel]
+* https://github.com/spring-projects/spring-retry[Spring Retry]
+
+== Core Concepts
+
+To create a circuit breaker in your code you can use the `CircuitBreakerFactory` API. When you include a Spring Cloud Circuit Breaker starter on your classpath a bean implementing this API will automatically be created for you.
+A very simple example of using this API is given below
+
+====
+[source,java]
+----
+@Service
+public static class DemoControllerService {
+	private RestTemplate rest;
+	private CircuitBreakerFactory cbFactory;
+
+	public DemoControllerService(RestTemplate rest, CircuitBreakerFactory cbFactory) {
+		this.rest = rest;
+		this.cbFactory = cbFactory;
+	}
+
+	public String slow() {
+		return cbFactory.create("slow").run(() -> rest.getForObject("/slow", String.class), throwable -> "fallback");
+	}
+
+}
+----
+====
+
+The `CircuitBreakerFactory.create` API will create an instance of a class called `CircuitBreaker`.
+The `run` method takes a `Supplier` and a `Function`.
+The `Supplier` is the code that you are going to wrap in a circuit breaker.
+The `Function` is the fallback that will be executed if the circuit breaker is tripped.
+The function will be passed the `Throwable` that caused the fallback to be triggered.
+You can optionally exclude the fallback if you do not want to provide one.
+
+=== Circuit Breakers In Reactive Code
+
+If Project Reactor is on the class path then you can also use `ReactiveCircuitBreakerFactory` for your reactive code.
+
+====
+[source,java]
+----
+@Service
+public static class DemoControllerService {
+	private ReactiveCircuitBreakerFactory cbFactory;
+	private WebClient webClient;
+
+
+	public DemoControllerService(WebClient webClient, ReactiveCircuitBreakerFactory cbFactory) {
+		this.webClient = webClient;
+		this.cbFactory = cbFactory;
+	}
+
+	public Mono<String> slow() {
+		return webClient.get().uri("/slow").retrieve().bodyToMono(String.class).transform(
+		it -> cbFactory.create("slow").run(it, throwable -> return Mono.just("fallback")));
+	}
+}
+----
+====
+
+The `ReactiveCircuitBreakerFactory.create` API will create an instance of a class called `ReactiveCircuitBreaker`.
+The `run` method takes with a `Mono` or `Flux` and wraps it in a circuit breaker.
+You can optionally profile a fallback `Function` which will be called if the circuit breaker is tripped and will be passed the `Throwable`
+that caused the failure.
+
+== Configuration
+
+You can configure your circuit breakers using by creating beans of type `Customizer`.
+The `Customizer` interface has a single method called `customize` that takes in the `Object` to customize.
+
+// TODO link to implementation docs

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

@@ -767,4 +767,8 @@ If you want to learn more about the Spring Cloud Release train compatibility, yo
 In order to disable this feature, set `spring.cloud.compatibility-verifier.enabled` to `false`.
 If you want to override the compatible Spring Boot versions, just set the
 `spring.cloud.compatibility-verifier.compatible-boot-versions` property with a comma separated list
-of compatible Spring Boot versions.
+of compatible Spring Boot versions.
+
+== Spring Cloud Circuit Breaker
+
+include::spring-cloud-circuitbreaker.adoc[]