背景：

当我们使用微服务时，若想在本地联调就需要启动多个服务，为了避免本地启动过多服务，现将注册中心等基础服务共用。当我们在服务A开发时，都是注册到同一个nacos，这样本地和开发环境的服务A就会同时存在，当调用服务时就会使用负载均衡选择服务，导致我们无法正常调试接口。这时我们可以选择使用灰度版本来进行服务的选择。

具体实现步骤如下：

1、我们在本地配置文件中添加版本头

这样我们服务注册到nacos中点击服务列表会发现服务中都会带VERSION

spring:
  cloud:
    nacos:
      discovery:
        metadata:
          VERSION: zhangsan

2、添加灰度服务接口

public interface GrayLoadBalancer {

	/**
	 * 根据serviceId 筛选可用服务
	 * @param serviceId 服务ID
	 * @param request 当前请求
	 * @return ServiceInstance
	 */
	ServiceInstance choose(String serviceId, ServerHttpRequest request);

}

3、灰度过滤器

import lombok.extern.slf4j.Slf4j;
import org.apache.http.util.Asserts;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.DefaultResponse;
import org.springframework.cloud.client.loadbalancer.LoadBalancerUriTools;
import org.springframework.cloud.client.loadbalancer.Response;
import org.springframework.cloud.gateway.config.LoadBalancerProperties;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.ReactiveLoadBalancerClientFilter;
import org.springframework.cloud.gateway.support.DelegatingServiceInstance;
import org.springframework.cloud.gateway.support.NotFoundException;
import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
import org.springframework.cloud.loadbalancer.support.LoadBalancerClientFactory;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;

import java.net.URI;

@Slf4j
@Component
public class GrayReactiveLoadBalancerClientFilter extends ReactiveLoadBalancerClientFilter {

    private final static String SCHEME = "lb";

    private static final int LOAD_BALANCER_CLIENT_FILTER_ORDER = 10150;
    private final GrayLoadBalancer grayLoadBalancer;
    private final LoadBalancerProperties loadBalancerProperties;

    public GrayReactiveLoadBalancerClientFilter(LoadBalancerClientFactory clientFactory, LoadBalancerProperties loadBalancerProperties, GrayLoadBalancer grayLoadBalancer) {
        super(clientFactory, loadBalancerProperties);
        this.loadBalancerProperties = loadBalancerProperties;
        this.grayLoadBalancer = grayLoadBalancer;
    }

    @Override
    public int getOrder() {
        return LOAD_BALANCER_CLIENT_FILTER_ORDER;
    }

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        URI url = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR);
        String schemePrefix = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR);

        // 直接放行
        if (url == null || (!SCHEME.equals(url.getScheme()) && !SCHEME.equals(schemePrefix))) {
            return chain.filter(exchange);
        }
        // 保留原始url
        ServerWebExchangeUtils.addOriginalRequestUrl(exchange, url);

        if (log.isTraceEnabled()) {
            log.trace(ReactiveLoadBalancerClientFilter.class.getSimpleName() + " url before: " + url);
        }

        return choose(exchange).doOnNext(response -> {

            if (!response.hasServer()) {
                throw NotFoundException.create(loadBalancerProperties.isUse404(),
                        "Unable to find instance for " + url.getHost());
            }

            URI uri = exchange.getRequest().getURI();

            // if the `lb:<scheme>` mechanism was used, use `<scheme>` as the default,
            // if the loadbalancer doesn't provide one.
            String overrideScheme = null;
            if (schemePrefix != null) {
                overrideScheme = url.getScheme();
            }

            DelegatingServiceInstance serviceInstance = new DelegatingServiceInstance(response.getServer(),
                    overrideScheme);

            URI requestUrl = LoadBalancerUriTools.reconstructURI(serviceInstance, uri);

            if (log.isTraceEnabled()) {
                log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);
            }
            exchange.getAttributes().put(ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR, requestUrl);
        }).then(chain.filter(exchange));
    }

    /**
     * 获取实例
     * @param exchange ServerWebExchange
     * @return ServiceInstance
     */
    private Mono<Response<ServiceInstance>> choose(ServerWebExchange exchange) {
        URI uri = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR);
        Asserts.notNull(uri, "uri");
        ServiceInstance serviceInstance = grayLoadBalancer.choose(uri.getHost(), exchange.getRequest());
        return Mono.just(new DefaultResponse(serviceInstance));
    }

}

4、基于客户端版本号灰度路由

当我们调用服务带版本号时会优先匹配带版本号的服务，若找不到则会随机选择一个服务

import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.map.MapUtil;
import cn.hutool.core.util.RandomUtil;
import cn.hutool.core.util.StrUtil;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.cloud.gateway.support.NotFoundException;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.stereotype.Component;

import java.util.List;
import java.util.stream.Collectors;

@Slf4j
@RequiredArgsConstructor
@Component
public class VersionGrayLoadBalancer implements GrayLoadBalancer {

	private final DiscoveryClient discoveryClient;

	/**
	 * 根据serviceId 筛选可用服务
	 * @param serviceId 服务ID
	 * @param request 当前请求
	 * @return ServiceInstance
	 */
	@Override
	public ServiceInstance choose(String serviceId, ServerHttpRequest request) {
		List<ServiceInstance> instances = discoveryClient.getInstances(serviceId);

		// 注册中心无实例 抛出异常
		if (CollUtil.isEmpty(instances)) {
			log.warn("No instance available for {}", serviceId);
			throw new NotFoundException("No instance available for " + serviceId);
		}

		// 获取请求version，无则随机返回可用实例
		String reqVersion = request.getHeaders().getFirst(CommonConstant.VERSION);
		if (StrUtil.isBlank(reqVersion)) {
			return instances.get(RandomUtil.randomInt(instances.size()));
		}

		// 遍历可以实例元数据，若匹配则返回此实例
		List<ServiceInstance> availableList = instances.stream()
				.filter(instance -> reqVersion
						.equalsIgnoreCase(MapUtil.getStr(instance.getMetadata(), CommonConstant.VERSION)))
				.collect(Collectors.toList());

		if (CollUtil.isEmpty(availableList)) {
			return instances.get(RandomUtil.randomInt(instances.size()));
		}
		return availableList.get(RandomUtil.randomInt(availableList.size()));

	}
}