1. Question: How to implement service registration and discovery in Spring Cloud?

Solution: Use registries such as Eureka, Zookeeper, Cloud Foundry, and Consul provided by Spring Cloud to implement service registration and discovery.
Sample code:

@EnableEurekaServer  
public class EurekaServerApplication {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(EurekaServerApplication.class, args);  
   }  
}

2. Question: How to implement distributed configuration in Spring Cloud?

Solution: Use Config Server and Config Client provided by Spring Cloud to implement distributed configuration.
Sample code:

@Configuration  
@EnableConfigServer  
public class ConfigServerApplication {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(ConfigServerApplication.class, args);  
   }  
}
@Configuration  
@EnableConfigClient  
public class ConfigClientApplication {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(ConfigClientApplication.class, args);  
   }  
}

3. Question: How to implement calls between services in Spring Cloud?

Solution: Use the Spring Cloud CLI provided by Spring Cloud to implement calls between services.
Sample code:

@FeignClient(name = "serviceA")  
public interface ServiceA {
    
      
   @GetMapping("/getInfo")  
   String getInfo();  
}

4. Question: How to implement distributed messaging in Spring Cloud?

Solution: Use RabbitMQ provided by Spring Cloud to implement distributed messaging.
Sample code:

@Configuration  
@EnableRabbitMQ  
public class RabbitMQConfiguration {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(RabbitMQConfiguration.class, args);  
   }  
}
@Service  
public class MessageService {
    
      
   @Autowired  
   private RabbitTemplate rabbitTemplate;
   public void sendMessage(String message) {
    
      
       rabbitTemplate.convertAndSend("hello", message);  
   }  
}

5. Question: How to implement routing in Spring Cloud?

Solution: Use Spring Cloud Gateway provided by Spring Cloud to implement routing.
Sample code:

@Configuration  
@EnableGatewayServer  
public class GatewayServerConfiguration {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(GatewayServerConfiguration.class, args);  
   }  
}
@Configuration  
@EnableGatewayClient  
public class GatewayClientConfiguration {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(GatewayClientConfiguration.class, args);  
   }  
}

6. Question: How to implement global locking in Spring Cloud?

Solution: Use the Hystrix command provided by Spring Cloud to achieve global locking.
Sample code:

@Bean  
public HystrixCommand<String> command() {
    
      
   return new HystrixCommand<String>(() -> serviceA.getInfo());  
}

7. Question: How to implement circuit breaker in Spring Cloud?

Solution: Use the Hystrix command provided by Spring Cloud to implement the circuit breaker.
Sample code:

@Bean  
public HystrixCommand<String> command() {
    
      
   return new HystrixCommand<String>(() -> serviceA.getInfo());  
}

8. Question: How to implement load balancing in Spring Cloud?

Solution: Use the Ribbon provided by Spring Cloud to achieve load balancing.
Sample code:

@Configuration  
@EnableRibbonServer  
public class RibbonServerConfiguration {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(RibbonServerConfiguration.class, args);  
   }  
}
@Configuration  
@EnableRibbonClient  
public class RibbonClientConfiguration {
    
      
   public static void main(String[] args) {
    
      
       SpringApplication.run(RibbonClientConfiguration.class, args);  
   }  
}

9. Question: How to implement leader election and cluster status monitoring in Spring Cloud?

Solution: Use Consul provided by Spring Cloud to implement leader election and cluster status monitoring.
The following is a simple sample code for leader election and cluster status monitoring using Spring Cloud and Consul.
First, the dependencies of Spring Cloud and Consul need to be introduced into the application:

<dependency>  
   <groupId>org.springframework.cloud</groupId>  
   <artifactId>spring-cloud-starter-netflix-consul-discovery</artifactId>  
</dependency>

Then, you need to configure Consul, you can add the following configuration in application.properties:

spring.profiles.active=consul  
consul.host=consul-host  
consul.port=8500  
consul.path=/my-app  
consul.service-name=my-app

Among them, consul-hostis the address of the Consul service, /my-appis the path where the application configuration is stored in Consul, and my-appis the name of the application.
Next, you can implement a leader election class, using Consul's Leader Election function. In this example, we use a simple RandomLeader election algorithm, but in practice more complex algorithms can be implemented, such as Raft.

import org.springframework.beans.factory.annotation.Value;  
import org.springframework.cloud.client.discovery.ConsulClient;  
import org.springframework.cloud.netflix.eureka.EurekaClient;  
import org.springframework.context.annotation.Bean;  
import org.springframework.context.annotation.Configuration;  
import org.springframework.context.annotation.Primary;  
import org.springframework.core.io.ClassPathResource;  
import org.springframework.core.io.Resource;  
import org.springframework.core.style.粝；
import java.io.IOException;  
import java.util.ArrayList;  
import java.util.List;  
import java.util.Random;
@Configuration  
@Primary  
public class LeaderElectionConfig {
    
    
   @Value("${consul.host}")  
   private String consulHost;
   @Value("${consul.port}")  
   private int consulPort;
   @Value("${consul.path}")  
   private String consulPath;
   @Value("${consul.service-name}")  
   private String serviceName;
   @Bean  
   public ConsulClient consulClient() {
    
      
       return new ConsulClient(consulHost, consulPort, serviceName);  
   }
   @Bean  
   public EurekaClient eurekaClient() {
    
      
       return new EurekaClient();  
   }
   @Bean  
   public RandomLeader randomLeader() {
    
      
       return new RandomLeader();  
   }
   private static class RandomLeader implements org.springframework.cloud.netflix.eureka.config.LeaderElection {
    
    
       private final Random random = new Random();
       @Override  
       public String elect(List<String> instances) {
    
      
           instances.add(0, serviceName);  
           int index = random.nextInt(instances.size());  
           return instances.get(index);  
       }  
   }  
}

In this configuration class, we define a ConsulClientbean to create the Consul client, a EurekaClientbean to create the Eureka client, and a RandomLeaderbean to implement the leader election algorithm. elect()method will add the application name to the instance list at election time, and then randomly select an instance to be the leader.
Finally, a Leader Election listener needs to be registered in the application so that the application can receive notifications when the leader changes. The following configuration can be added in application.properties:

spring.cloud.consul.leader-election. enabled=true

In this way, a simple combination of Spring Cloud and Consul for leader election and cluster status monitoring is implemented.

Spring Cloud common problem handling and code analysis

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