Lab#31 Circuit Breaker With Feign client

In this lab we implement the circuit breaker inside the accounts microservice. The accounts microservice uses Feign client to invoke cards and loans microservice.

If Spring Cloud CircuitBreaker is on the classpath and spring.cloud.openfeign.circuitbreaker.enabled=true, Feign will wrap all the methods with a circuit breaker.

Step#1 In the pom in the accounts microservice, add the dependency and change the version of spring-cloud.

    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.5.13</version>
        <relativePath/> 
    </parent>
    <groupId>com.tus</groupId>
    <artifactId>ma-labs-accounts-8081</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <java.version>17</java.version>
        <!-- Lab 16: Spring Cloud Version -->
        <spring-cloud.version>2024.0.0</spring-cloud.version>
    </properties>

Note: Changed in all services for compatibility reasons

          <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- Lab31 Circuit Breaker Pattern -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-circuitbreaker-reactor-resilience4j</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>

And in application.yml

  config:
   import: "configserver:http://localhost:8071/" # config server port 8071
  cloud:
    openfeign:
      circuitbreaker:
        enabled: true

Add in the parameters for the circuit breaker in the application.yml for the accounts service.

resilience4j.circuitbreaker:
  configs:
    default:
      slidingWindowSize: 10
      permittedNumberOfCallsInHalfOpenState: 2
      failureRateThreshold: 50
      waitDurationInOpenState: 10000 # 10 seconds

Step#2 Implementing the fallbacks. Create a new class called LoansFallback in the accounts microservice

Figure 1. Loans Fallback

package com.tus.accounts.service.client;

import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Component;

import com.tus.accounts.dto.LoansDto;

@Component
public class LoansFallback implements LoansFeignClient {

    @Override
    public ResponseEntity<LoansDto> fetchLoanDetails(String correlationId, String mobileNumber) {
        return null;
    }
}

Step#3 Create a similar class called CardsFallback

Figure 2. Cards Fallback

package com.tus.accounts.service.client;

import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Component;

import com.tus.accounts.dto.CardsDto;

@Component
public class CardsFallback implements CardsFeignClient {

    @Override
    public ResponseEntity<CardsDto> fetchCardDetails(String correlationId, String mobileNumber) {
        return null;
    }
}

Update the LoansFeignClient interface and the CardsFeignClient interface.

@FeignClient(name = "loans", fallback = LoansFallback.class) // Lab 31
public interface LoansFeignClient {
    @GetMapping(value = "/api/loans", consumes = "application/json")
    public ResponseEntity<LoansDto> fetchLoanDetails(@RequestHeader("tusbank-correlation-id") String correlationId,
            @RequestParam String mobileNumber);
}

@FeignClient(name = "cards", fallback = CardsFallback.class) // Lab 31
public interface CardsFeignClient {
    @GetMapping(value = "/api/cards", consumes = "application/json")
    public ResponseEntity<CardsDto> fetchCardDetails(@RequestHeader("tusbank-correlation-id") String correlationId,
            @RequestParam String mobileNumber);
}

Add the if statements in the CustomersServiceImpl class.

        if (null != loansDtoResponseEntity) { // Lab 31
            customerDetailsDto.setLoansDto(loansDtoResponseEntity.getBody());
        }

        ResponseEntity<CardsDto> cardsDtoResponseEntity = cardsFeignClient.fetchCardDetails(correlationId,
                mobileNumber);
        if (null != cardsDtoResponseEntity) { // Lab 31
            customerDetailsDto.setCardsDto(cardsDtoResponseEntity.getBody());
        }
        return customerDetailsDto;

Step#3 Start all the services, config, eureka, accounts, cards and loans followed by gateway.

• Eureka Dashboard: http://localhost:8070/

Figure 3. Eureka Dashboard

Open the actuator of accounts microservice. First make sure that the actuator endpoints are enabled by checking the application.yml

management:
  endpoints:
    web:
      exposure:
        include: "*" # Lab 19, 31
        # include: info, shutdown # lab 22 info, lab 23 shutdown
  endpoint:
    shutdown:
      enabled: true

• Accounts Actuator Endpoints: http://localhost:8081/actuator

Figure 4. Actuator Endpoints

Check the circuit breakers link. Right now there are no circuit breakers because we did not send any request yet.

• Circuit Breakers: http://localhost:8081/actuator/circuitbreakers

Figure 5. Actuator Circuitbreakers

Call the fetch customer details endpoint.

• Fetch Customer Details Endpoint: http://localhost:8072/tusbank/accounts/api/customers?mobileNumber=1234567899

Figure 6. Accounts Fetch Customer Details Endpoint

---

Note: account, loan and card previously created for this mobile number.

POST localhost:8072/tusbank/accounts/api/accounts

{
    "name": "Joe O'Regan",
    "email": "joe@student.tus.ie",
    "mobileNumber": "1234567899"    
}

POST localhost:8072/tusbank/loans/api/loans?mobileNumber=1234567899

{
    "email": "joe@student.tus.ie",
    "loanType": "Home Loan",
    "totalLoan": 100000,
    "amountPaid": 0,
    "outstandingAmoutn": 100000
}

POST localhost:8072/tusbank/cards/api/cards?mobileNumber=1234567899

{
    "name": "Joe O'Regan",
    "email": "joe@student.tus.ie",
    "mobileNumber": "0871234567"    
}

---

Now refresh the actuator end point

Figure 7. Actuator Circuitbreakers

And look at the circuit breaker events.

Figure 8. Actuator Circuitbreaker Events

---

Step#4 To look at the negative situation, first stop the loans microservice from the springboot dashboard

Figure 9. Stop Loans Microservice

Call the fetch customer details endpoint again

Figure 10. Call Fetch Customer Details Endpoint

Try calling the endpoint a number of times and the circuit breaker will move to the open state.

Figure 11. Circuit Breaker Moves To Open State

Figure 12. Closed to Open State