<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-gateway</artifactId>
        <version>3.0.2</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

<properties>
    <nacos.version>2021.1</nacos.version>
</properties>

//fhadmin.cn
server:
  port: 9040
spring:
  application:
    name: gateway
  cloud:
    gateway:
      routes:
        - id: consumer
          uri: lb://consumer
          #          uri: http://localhost:9010
          predicates:
            - Path=/**
    nacos:
      discovery:
        server-addr: localhost:8848
        metadata:
          preserved.heart.beat.interval: 3 #心跳间隔。时间单位:秒。心跳间隔
          preserved.heart.beat.timeout: 6 #心跳暂停。时间单位:秒。 即服务端6秒收不到客户端心跳，会将该客户端注册的实例设为不健康：
          preserved.ip.delete.timeout: 9 #Ip删除超时。时间单位:秒。即服务端9秒收不到客户端心跳，会将该客户端注册的实例删除：

当我通过uri: http://localhost:9010去调用服务时，是可以调用的，但是当我用uri lb://consumer时就无法调用服务，报错503.
解决办法是：
加入feign依赖。

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-gateway</artifactId>
        <version>3.0.2</version>
    </dependency>
    <!--fegin组件-->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-openfeign</artifactId>
        <version>3.0.2</version>
    </dependency>
    <!-- Feign Client for loadBalancing -->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-loadbalancer</artifactId>
        <version>3.0.2</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

猜测原因：nacos兼容feign，feign集成ribbon，默认实现负载均衡；或许是nacos不兼容springcloud gateway自带的ribbon。实现案例 fhadmin.cn