一、Ribbon负载均衡服务调用

概述

Ribbon负载均衡演示

Ribbon是客户端（消费者）负载均衡的工具。

Ribbon的POM

  <!--Ribbon的依赖-->
  <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
 </dependency>

升级最新版本，eureka自带Ribbon的依赖

RestTemplate

@LoadBalanced注解给RestTemplate开启负载均衡的能力。

官方文档：https://docs.spring.io/spring-framework/docs/5.2.2.RELEASE/javadoc-api/org/springframework/web/client/RestTemplate.html

getForObject/getForEntity方法

测试getForEntity方法

    @GetMapping("/consumer/payment/getForEntity/{id}")
    public CommonResult<Payment> getPayment2(@PathVariable("id") Long id){
        ResponseEntity<CommonResult> entity = restTemplate.getForEntity(PAYMENT_URL + "/payment/get/" + id, CommonResult.class);
        if (entity.getStatusCode().is2xxSuccessful()){
            return entity.getBody();
        }else {
            return new CommonResult<>(444,"操作失败");
        }
    }

重启测试

Ribbon核心组件IRule

IRule:根据特定的算法从服务列表中选取一个要访问的服务。
IRule接口的实现：

负载均衡常用规则：默认为RoundRobinRule轮询。

替换规则

Ribbon的自定义配置类不可以放在@ComponentScan所扫描的当前包下以及子包下，否则这个自定义配置类就会被所有的Ribbon客户端共享，达不到为指定的Ribbon定制配置，而@SpringBootApplication注解里就有@ComponentScan注解，所以不可以放在主启动类所在的包下。（因为Ribbon是客户端（消费者）这边的，所以Ribbon的自定义配置类是在客户端（消费者）添加，不需要在提供者或注册中心添加）

1. 重新创建项目包
   
2. 创建MySelfRule规则类

@Configuration
public class MySelfRule {
    
    @Bean
    public IRule myRule(){
    	// 随机
        return new RandomRule();
    }
}

3. 主启动添加@RibbonClient(name = "CLOUD-PAYMENT-SERVICE", configuration = MySelfRule.class)，告诉服务用那种负载模式

@SpringBootApplication
@EnableEurekaClient
@RibbonClient(name = "CLOUD-PAYMENT-SERVICE", configuration = MySelfRule.class)
public class OrderMain80 {
    public static void main(String[] args) {
        SpringApplication.run(OrderMain80.class);
    }
}

4. 启动测试，浏览器输入http://localhost/consumer/payment/get/1，多次刷新实现负载均衡为随机。

Ribbon负载均衡算法

原理（RoundRobinRule原理）

源码（RoundRobinRule）

    public Server choose(ILoadBalancer lb, Object key) {
        if (lb == null) {
            log.warn("no load balancer");
            return null;
        }

        Server server = null;
        int count = 0;
        while (server == null && count++ < 10) {
            List<Server> reachableServers = lb.getReachableServers();
            List<Server> allServers = lb.getAllServers();
            int upCount = reachableServers.size();
            int serverCount = allServers.size();

            if ((upCount == 0) || (serverCount == 0)) {
                log.warn("No up servers available from load balancer: " + lb);
                return null;
            }

            int nextServerIndex = incrementAndGetModulo(serverCount);
            server = allServers.get(nextServerIndex);

            if (server == null) {
                /* Transient. */
                Thread.yield();
                continue;
            }

            if (server.isAlive() && (server.isReadyToServe())) {
                return (server);
            }

            // Next.
            server = null;
        }

        if (count >= 10) {
            log.warn("No available alive servers after 10 tries from load balancer: "
                    + lb);
        }
        return server;
    }

    /**
     * Inspired by the implementation of {@link AtomicInteger#incrementAndGet()}.
     *
     * @param modulo The modulo to bound the value of the counter.
     * @return The next value.
     */
    private int incrementAndGetModulo(int modulo) {
        for (;;) {
            int current = nextServerCyclicCounter.get();
            int next = (current + 1) % modulo;
            if (nextServerCyclicCounter.compareAndSet(current, next))
                return next;
        }
    }

手写负载算法

1. 启动7001、7002 eureka集群
2. 修改8001、8002的controller

    @GetMapping(value = "/payment/lb")
    public String getPaymentLB(){
        return serverPort;
    }

3.80订单微服务改造

• 去掉ApplicationContextConfig里restTemplate方法上的@LoadBalanced注解。
• 在springcloud包下新建lb.ILoadBalancer接口（自定义负载均衡机制（面向接口））

public interface ILoadBalancer {
    //传入具体实例的集合，返回选中的实例
    ServiceInstance instance(List<ServiceInstance> serviceInstances);
}

• 在lb包下新建自定义ILoadBalancer接口的实现类

@Component
public class MyLB implements LoadBalancer {

    private AtomicInteger atomicInteger = new AtomicInteger(0);

    public final int getAndIncrement() {
        int current;
        int next;
        // 自旋锁
        do {
            current = this.atomicInteger.get();
            next = current >= 2147483647 ? 0 : current + 1;
        } while (!this.atomicInteger.compareAndSet(current,next));
        System.out.println("******第几次访问，next: "+next);
        return next;
    }

    @Override
    public ServiceInstance instance(List<ServiceInstance> serviceInstances) {
        int index = getAndIncrement() % serviceInstances.size();

        return serviceInstances.get(index);
    }
}

• 修改controller

   @Resource
    private RestTemplate restTemplate;

    @Resource
    private LoadBalancer loadBalancer;
    
    @GetMapping("/consumer/payment/lb")
    public String getPaymentLB() {
        List<ServiceInstance> instances = discoveryClient.getInstances("CLOUD-PAYMENT-SERVICE");
        if (instances == null || instances.size() <= 0){
            return null;
        }
        ServiceInstance serviceInstance = loadBalancer.instance(instances);
        URI uri = serviceInstance.getUri();
        return  restTemplate.getForObject(uri+"/payment/lb",String.class);
    }

二、OpenFeign服务接口调用

概述

官网文档：https://cloud.spring.io/spring-cloud-static/Hoxton.SR1/reference/htmlsingle/#spring-cloud-openfeign

Feign是一个声明式的web服务客户端，让编写web服务客户端变得非常容易，只需创建一个接口并在接口上添加注解即可。

OpenFeign和Feign的区别

OpenFeign使用在客户端（消费测）

使用步骤

1. 新建模块
   
2. 改POM

  <dependencies>
        <!-- openfeign -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- eureka-client -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <!-- 引用自己定义的api通用包，可以使用Payment支付Entity -->
        <dependency>
            <groupId>com.zhao.springcloud</groupId>
            <artifactId>cloud-api-commons</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <!--热部署-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

3. 写YML

server:
  port: 80 

eureka:
  client:
    register-with-eureka: false
    service-url:
      defaultZone: http://eureka7001.com:7001/eureka,http://eureka7002.com:7002/eureka,http://eureka7003.com:7003/eureka

4. 主启动类

@SpringBootApplication
// 激活开启feign
@EnableFeignClients
public class OrderFeign {
    public static void main(String[] args) {
        SpringApplication.run(OrderFeign.class);
    }
}

5. 业务类

@Component
@FeignClient(value = "CLOUD-PAYMENT-SERVICE")
public interface PaymentFeignService {

    @GetMapping("/payment/get/{id}")
    public CommonResult getPaymentById(@PathVariable("id") Long id);
}

6. 编写controller

@RestController
@Slf4j
public class OrderFeignController {
    @Resource
    private PaymentFeignService paymentFeignService;
    @GetMapping("/consumer/payment/get/{id}")
    public CommonResult<Payment> getPaymentById(@PathVariable("id") Long id){
        return paymentFeignService.getPaymentById(id);
    }
}

7.启动测试
自带负载均衡功能

OpenFeign超时控制

提供者在处理服务时用了3秒，提供者认为花3秒是正常，而消费者只愿意等1秒，1秒后，提供者会没返回数据，消费者就会造成超时调用报错。所以需要双方约定好时间，不使用默认的。

模拟超时出错的情况

1. 在8001的PaymentController里添加：（模拟服务处理时间长）

    @GetMapping("/payment/feign/timeout")
    public String paymentFeignTimeout(){
        try{
            TimeUnit.SECONDS.sleep(3);
        }catch (InterruptedException e){
            e.printStackTrace();
        }
        return serverPort;
    }

2. 在80的PaymentFeignService中添加：

	@GetMapping("/payment/feign/timeout")
    public String paymentFeignTimeout();

3. 然后在80的OrderFeignController中添加：

    @GetMapping("/consumer/payment/feign/timeout")
    public String paymentFeignTimeout(){
        //openFeign-ribbon，客户端一般默认等待1秒
        return paymentFeignService.paymentFeignTimeout();
    }

4. 测试
   
   
5. YML开启超时时间

#没提示不管它，可以设置
ribbon:
  #指的是建立连接后从服务器读取到可用资源所用的时间
  ReadTimeout: 5000
  #指的是建立连接使用的时间，适用于网络状况正常的情况下，两端连接所用的时间
  ConnectTimeout: 5000

6. 重新测试
   

OpenFeign日志打印功能

概述

打印级别

设置步骤

• 配置日志bean

@Configuration
public class FeignConfig {
    @Bean
    Logger.Level feignLogLevel(){
        return Logger.Level.FULL;
    }
}

• Yml中开启日志

logging:
  level:
  #feign日志以什么级别监控哪个接口
    com.zhao.springcloud.service.PaymentFeignService: debug

• 测试
  
  

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