OpenFeign、RestTemplate支持自定义服务地址列表

一、背景

最近在支援项目时，项目组需要将后端服务部署为多个实例，且没有集成服务注册中心、反向代理、K8S等，如此提出需要客户端OpenFeign、RestTemplate等支持手动配置服务端地址列表，并支持在服务端实例间负载均衡，经过调研后给出如下基于Spring Cloud LoadBalancer的集成方案。

二、解决思路

OpenFeign、RestTemplate均是通过url对服务发起调用，具体url的负载均衡则是由Spring Cloud LoadBalancer负责，所以需要在LoadBalancer上做文章，查询相关文档后给出如下思路：

• 通过@LoadBalancerClient(name, configuration)注解为不同服务标识指定相应的配置类
  • 服务标识 对应@FeignClient.name，或 RestTemplate调用url http://serviceId/path中的serviceId
• 然后在相应的配置类中注册自定义的ServiceInstanceListSupplier
• 最后在自定义的ServiceInstanceListSupplier中返回该服务标识手动配置的服务端地址列表

接下来给出核心实现代码。

三、定义通用配置

首先，自定义配置属性如下：

import org.springframework.boot.context.properties.ConfigurationProperties;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 负载均衡静态配置
 *
 * @author luohq
 * @date 2024-04-25 9:35
 */
@ConfigurationProperties(prefix = LoadBalancerStaticProps.PREFIX)
public class LoadBalancerStaticProps {

    public static final String PREFIX = "spring.cloud.loadbalancer.clients";
    /**
     * 客户端ServiceId到静态地址列表的映射
     */
    private Map<String, List<String>> staticUris = new HashMap<>();

    public Map<String, List<String>> getStaticUris() {
        return staticUris;
    }

    public void setStaticUris(Map<String, List<String>> staticUris) {
        this.staticUris = staticUris;
    }

    @Override
    public String toString() {
        return "LoadBalancerStaticProps{" +
                "staticUris=" + staticUris +
                '}';
    }
}
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后续可通过如下示例配置，手动指定不同服务标识对应的服务端地址列表：

spring:
  cloud:
    loadbalancer:
      clients:
        # 配置负载均衡静态地址
        static-uris:
          # app-rbac服务的静态地址列表
          app-rbac:
            - http://localhost:8081
            - http://localhost:8082
          # app-atom服务的静态地址列表
          app-atom:
            - http://localhost:9081
            - http://localhost:9082
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四、定义通用StaticServiceInstanceListSuppler

StaticServiceInstanceListSuppler实现了ServiceInstanceListSupplier接口，
这个接口是Spring Cloud LoadBalancer的一部分，是一个通用的客户端负载均衡器。
StaticServiceInstanceListSuppler支持自定义serviceId对应的服务地址列表serviceStaticUriList，
同时提供create方法，支持从前文定义的配置属性LoadBalancerStaticProps 中（即从配置文件中）获取serviceId对应的服务地址列表。

import org.springframework.cloud.client.DefaultServiceInstance;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier;
import org.springframework.util.Assert;
import reactor.core.publisher.Flux;

import java.net.URI;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

/**
 * 静态服务地址提供器
 *
 * @author luohq
 * @date 2024-04-25
 */
public class StaticServiceInstanceListSuppler implements ServiceInstanceListSupplier {

    /**
     * 服务标识
     */
    private final String serviceId;

    /**
     * 服务地址列表
     */
    private final List<String> serviceStaticUriList;

    public StaticServiceInstanceListSuppler(String serviceId, List<String> serviceStaticUriList) {
        Assert.notNull(serviceId, "serviceId may not be null");
        Assert.notEmpty(serviceStaticUriList, "serviceStaticUriList may not be null");
        this.serviceId = serviceId;
        this.serviceStaticUriList = serviceStaticUriList;
    }

    @Override
    public String getServiceId() {
        return serviceId;
    }

    @Override
    public Flux<List<ServiceInstance>> get() {
        List<ServiceInstance> defaultServiceInstanceList = IntStream.range(0, serviceStaticUriList.size())
                .mapToObj(i -> {
                    DefaultServiceInstance defaultServiceInstance = new DefaultServiceInstance();
                    defaultServiceInstance.setServiceId(this.serviceId);
                    defaultServiceInstance.setInstanceId(this.serviceId + i);
                    defaultServiceInstance.setUri(URI.create(serviceStaticUriList.get(i)));
                    return defaultServiceInstance;
                })
                .collect(Collectors.toList());
        return Flux.just(defaultServiceInstanceList);
    }

    public static StaticServiceInstanceListSuppler create(String serviceId, LoadBalancerStaticProps loadBalancerStaticProps) {
        return new StaticServiceInstanceListSuppler(serviceId, loadBalancerStaticProps.getStaticUris().get(serviceId));
    }
}
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五、为指定serviceId定义专属的配置类

如下实现即对应serviceId=app-rbac服务的专属配置类，
不同的serviceId可再单独定义相应的配置类。

import org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Primary;
/**
 * RBAC客户端负载均衡静态配置
 *
 * @author luohq
 * @date 2024-04-25 9:35
 */
public class RbacClientLoadBalancerStaticConfiguration {

    public static final String SERVICE_ID = "app-rbac";

    @Bean
    @Primary
    public ServiceInstanceListSupplier serviceInstanceListSupplier(LoadBalancerStaticProps loadBalancerStaticProps) {
        return StaticServiceInstanceListSuppler.create(SERVICE_ID, loadBalancerStaticProps);
    }
}
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六、通过@LoadBalancerClient为指定serviceId设置配置类

6.1 OpenFeign

如果项目中使用的是OpenFeign，以下配置已足够：

import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClients;
import org.springframework.context.annotation.Configuration;

/**
 * RBAC客户端负载均衡静态配置
 *
 * @author luohq
 * @date 2024-04-25 9:35
 */
@Configuration
@LoadBalancerClients({
        //自定义RBAC服务配置
        @LoadBalancerClient(
                name = RbacClientLoadBalancerStaticConfiguration.SERVICE_ID,
                configuration = RbacClientLoadBalancerStaticConfiguration.class
        )
})
@EnableConfigurationProperties({LoadBalancerStaticProps.class})
public class LoadBalancerStaticConfiguration2 {
    
}
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6.2 RestTemplate

如果项目中使用的是RestTemplate，那么还需要通过@LoadBalanced注解设置RestTemplate支持负载均衡，
具体配置代码如下：

import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClients;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

/**
 * RBAC客户端负载均衡静态配置
 *
 * @author luohq
 * @date 2024-04-25 9:35
 */
@Configuration
@LoadBalancerClients({
        //自定义RBAC服务配置
        @LoadBalancerClient(
                name = RbacClientLoadBalancerStaticConfiguration.SERVICE_ID,
                configuration = RbacClientLoadBalancerStaticConfiguration.class
        )
})
@EnableConfigurationProperties({LoadBalancerStaticProps.class})
public class LoadBalancerStaticConfiguration2 {

    /**
     * 通过@LoadBalanced注解开启RestTemplate负载均衡能力
     */
    @LoadBalanced
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}
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七、Debug调试

Spring Cloud LoadBalancer默认使用的是RoundRobinLoadBalancer，可重点关注RoundRobinLoadBalancer中获取服务实例的代码。

---

参考：
https://spring.io/guides/gs/spring-cloud-loadbalancer
https://juejin.cn/post/7266315019294490661
https://docs.spring.io/spring-cloud-commons/docs/3.1.8/reference/html/#spring-cloud-loadbalancer