Java Microservice Interview Questions

#How to create Eureka Server?

1. Add the dependency of spring-cloud-starter-netflix-eureka-server.

2. Use @EnableEurekaServer

   @SpringBootApplication
   @EnableEurekaServer
   public class Application {
       public static void main(String[] args) {
           new SpringApplicationBuilder(Application.class).web(true).run(args);
       }
   }
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3. • Standalone Mode

     server:
       port: 8761
     eureka:
       instance:
         hostname: localhost
       client:
         registerWithEureka: false
         fetchRegistry: false
         serviceUrl:
           defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/
             ```
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   • Peer Aware Mode

     For Peer Aware mode, you run the same application twice with different profiles.

     First Profile:

     spring:
         profiles: peer1
       eureka:
         instance:
           hostname: peer1
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     Second Profile:

     spring:
           profiles: peer2
         eureka:
           instance:
             hostname: peer2
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#How to Register with Eureka?

1. You need to have spring-cloud-starter-netflix-eureka-client in you classpath
2. Giving Eureka Server address in application.yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
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3. If in Peer mode You can give multiple peer address:

eureka:
  client:
    serviceUrl:
      defaultZone: https://peer1/eureka/,http://peer2/eureka/,http://peer3/eureka/
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#How do you secure Eureka Sever?

1. Add spring-boot-starter-security to the class path
2. Web Security Config to your app for disabling csrf.

@EnableWebSecurity
class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.csrf().ignoringAntMatchers("/eureka/**");
        super.configure(http);
    }
}
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3. Provide Spring Security User name and password in application.yml

spring:
  security:
    user:
      name: admin
      password: pwd
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4. Change the default zone url accordingly.

defaultZone:  http://admin:pwd@localhost:8761/eureka/
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#How to enable Hystrix Circuit Breaker?

@Bean
public Customizer<HystrixCircuitBreakerFactory> defaultConfig() {
    return factory -> factory.configureDefault(id -> HystrixCommand.Setter
            .withGroupKey(HystrixCommandGroupKey.Factory.asKey(id))
            .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
            .withExecutionTimeoutInMilliseconds(4000)));
}
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#How to write hystrix client?

1. Include spring-cloud-starter-netflix-hystrix in you classpath
2. Miminal Hystrix Client:

@SpringBootApplication
@EnableCircuitBreaker
public class Application {
    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }
}
@Component
public class StoreIntegration {
    @HystrixCommand(fallbackMethod = "defaultStores")
    public Object getStores(Map<String, Object> parameters) {
        //do stuff that might fail
    }
    public Object defaultStores(Map<String, Object> parameters) {
        return /* something useful */;
    }
}
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#What are the common Hystrix Circuit Breaker configuration?

• circuitBreaker.enabled
• circuitBreaker.requestVolumeThreshold
• circuitBreaker.sleepWindowInMilliseconds
• circuitBreaker.errorThresholdPercentage
• circuitBreaker.forceOpen
• circuitBreaker.forceClosed

These above you can use with @HystrixProperty annotation.