Spring Boot Resilience4j Circuitbreaker Annotation Example

Vikas Ve2ma
technical
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Introduction

This is continuation of my previous blog on Resilience4j. In this blog, we shall try to use the annotation and external configuration for the circuit breaker implementation.

So let’s start by creating a basic application. Our application would have one controller and one service class.

We already saw how to make the reactive basic application in a previous blog. Now we will continue from that.

Version Details

  • spring-boot:2.2.6.RELEASE
  • spring-cloud:Hoxton.SR4
  • Resilience4j:1.1.0
  • Java:11
  • Kotlin:1.3.71

Adding dependencies

We need to add the following dependencies in the project -

  • resilience4j-reactor
  • resilience4j-circuitbreaker
  • resilience4j-spring-boot2
  • spring-boot-starter-actuator
  • spring-boot-starter-aop

Add configuration for the circuit breaker

Open application.yml and add the following configuration for the circuit breaker -

resilience4j.circuitbreaker:
  instances:
    processService:
      slidingWindowSize: 50
      permittedNumberOfCallsInHalfOpenState: 3
      slidingWindowType: TIME_BASED
      minimumNumberOfCalls: 20
      waitDurationInOpenState: 50s
      failureRateThreshold: 50

The detail of the configuration is as below -

resilience4j.circuitbreaker

it is the header of the configuration, the circuitbreaker specify that this configuration contains all the configuration for the circuit breaker.

processService

It is the name of this configuration that would be applied to the service.

slidingWindowSize

Configures the size of the sliding window which is used to record the outcome of calls when the CircuitBreaker is closed.

permittedNumberOfCallsInHalfOpenState

Configures the number of permitted calls when the CircuitBreaker is half open.

slidingWindowType

Configures the type of the sliding window which is used to record the outcome of calls when the CircuitBreaker is closed.

minimumNumberOfCalls

Configures the minimum number of calls which are required (per sliding window period) before the CircuitBreaker can calculate the error rate or slow call rate.

waitDurationInOpenState

The time that the CircuitBreaker should wait before transitioning from open to half-open.

failureRateThreshold

Configures the failure rate threshold in percentage. When the failure rate is equal or greater than the threshold the CircuitBreaker transitions to open and starts short-circuiting calls.

Add circuit broker to the service

Now modify the service method to add the circuit breaker. For that we need to add the @CircuitBreaker annotation at the service method and provide the callback method name like this

@CircuitBreaker(name="processService", fallbackMethod = "fallbackProcess")

The fallback method name is fallbackProcess it should be in the same class and it should have the same signature but with an extra parameter for the Throwable class for the exception handling.

So our service method and fallback method should look like this

@CircuitBreaker(name="processService", fallbackMethod = "fallbackProcess")
fun process(id: Int): Mono<String> {
  return if (id < 1) Mono.error{ IllegalArgumentException("oh!! invalid id") }
    else Mono.just("Id Found!")
}

fun fallbackProcess(id: Int, exp: Throwable): Mono<String> {
    log.error("eh!!! this is the error ${exp.localizedMessage}")
    return Mono.just("From fallback method: Id Not found ")
}

Run Application

Let’s start the application and run the following script on the terminal

http :8080/process?id=1

Output

$ http :8080/process?id=1
HTTP/1.1 200 OK
Content-Type: text/event-stream;charset=UTF-8
transfer-encoding: chunked

data:Id Found!
$

Now let’s try to fail the service sending the id param value as less than 1 as below

http :8080/process?id=0

Output

$ http :8080/process?id=0
HTTP/1.1 200 OK
Content-Type: text/event-stream;charset=UTF-8
transfer-encoding: chunked

data:From fallback method: Id Not found
$

Source Code

The full source code is available at GitHub

Reference