resilience4j + Spring instance of CircuitBreaker - spring

Question

I would like to use Resilience4j to deal with fault tolerance, I am using CircuitBreaker and TimerLimit.
I would like to separate business logic of fault tolerance behavior, to not "dirty" my business code.
So, I am thinking to use Command pattern to execute my methods that will be treat, like Hystrix do with HystrixCommand.
Example:
public class MyCommand {
private static final CircuitBreaker circuitBreaker;
private Long param1, param2;
private MyService myService;
private static final TimeLimiter timeLimiter;
static {
long ttl = 50000;
TimeLimiterConfig configTimerLimit
= TimeLimiterConfig.custom().timeoutDuration(Duration.ofMillis(ttl)).build();
timeLimiter = TimeLimiter.of(configTimerLimit);
// I got the configuration from a class that I created.
circuitBreaker = CircuitBreaker.of("my", CircuitBreakerConfigOptions.defaultForExternalService());
}
public MyCommand(Long param1, Long param2, MyService myService) {
this.param1 = param1;
this.param2 = param2;
this.myService = myService;
}
public String run() {
Callable<String> stringCallable = TimeLimiter.decorateFutureSupplier(timeLimiter,
() -> CompletableFuture.supplyAsync(() -> myService.hello(param1, param2)));
Callable<String> callable = CircuitBreaker.decorateCallable(circuitBreaker, stringCallable);
return Try.of(callable::call).recover(t -> fallback(t)).get();
}
protected String fallback(Throwable throwable) {
Callable<String> stringCallable = TimeLimiter.decorateFutureSupplier(timeLimiter,
() -> CompletableFuture.supplyAsync(() -> myService.otherHello(param1, param2)));
return Try.of(stringCallable::call).getOrElse("Fallback");
}
}
Calling in my Controller:
#ApiOperation(value = "Only to test")
#GetMapping(value = "/execute", produces = MediaType.APPLICATION_JSON)
public String execute() {
return new MyCommand(1L, 2L, new MyService()).run();
}
My doubts:
1 - In this case, circuitBreaker really needs to be static, because I understood that the same object needs to be shared between the same method that you want to threat, I am right?
2 - How I have many instances of this application, circuitBreaker works individually for each instance? I am right?

Answer 1

What I understand from your question is - You need a Resilience4j's circuit breaker which should be sperate i.e. not messed with your business logic.
So I would suggest put circuit breaker protection around run() method. below code will elaborate -
Your Controller -
#ApiOperation(value = "Only to test")
#GetMapping(value = "/execute", produces = MediaType.APPLICATION_JSON)
public String execute() {
return new MyCommand().run();
}
Now Write your run() method of MyCommand class with #CircuitBreaker
public class MyCommand {
#CircuitBreaker(name = "RUN_METHOD_PROTECTION") // <---- here is our circuit breaker annotation code top of below your business code... and that’s it.
Your_Response run(Your_Request){
// Your business logic written here...
}
Further add circuit breaker configuration in your YAML property file as below (Count based I have used instead of time-based) –
resilience4j.circuitbreaker:
backends:
RUN_METHOD_PROTECTION:
registerHealthIndicator: true
slidingWindowSize: 100 # start rate calc after 100 calls
minimumNumberOfCalls: 100 # minimum calls before the CircuitBreaker can calculate the error rate.
permittedNumberOfCallsInHalfOpenState: 10 # number of permitted calls when the CircuitBreaker is half open
waitDurationInOpenState: 10s # time that the CircuitBreaker should wait before transitioning from open to half-open
failureRateThreshold: 50 # failure rate threshold in percentage
slowCallRateThreshold: 100 # consider all transactions under interceptor for slow call rate
slowCallDurationThreshold: 2s # if a call is taking more than 2s then increase the error rate
recordExceptions: # increment error rate if following exception occurs
- org.springframework.web.client.HttpServerErrorException
- java.io.IOException
- org.springframework.web.client.ResourceAccessException
Now if you are unable to use annotation #CircuitBreaker in your project then you can also do things in functional way i.e.
Let say we you have defined a bean in your configuration,
#Bean
public CircuitBreaker MyCircuitBreaker(){
CircuitBreakerConfig config = CircuitBreakerConfig.custom()
.slidingWindow(100,100, CircuitBreakerConfig.SlidingWindowType.COUNT_BASED)
.failureRateThreshold(50)
.build();
CircuitBreakerRegistry registry = CircuitBreakerRegistry.of(config);
CircuitBreaker circuitBreaker = registry.circuitBreaker("your_run_method_CircuitBreker"); // here you are registering your circuit breaker with a unique tag. And in future you refer this tag you get a same circuit breaker.
return circuitBreaker;
}
Now Your controller code would be below -
private CircuitBreaker circuitBreaker; // Assume you have injected the value from CircuitBreaker bean
#ApiOperation(value = "Only to test")
#GetMapping(value = "/execute", produces = MediaType.APPLICATION_JSON)
public String execute() {
Function<Your_Request, Your_Response> decorated = CircuitBreaker
.decorateFunction(circuitBreaker, new MyCommand().run());
return decorated.apply();
}
This way too you have never interfered with your business logic.

Answer 2

Since it seems that you are using Spring Boot, you could use the resilience4j-spring-boot-2 starter module which also has support for annotations.
https://resilience4j.readme.io/docs/getting-started-3