解决：java.lang.IllegalStateException: Annotation @EnableCircuitBreaker found, but there are no implementations. Did you forget to include a starter?

在主类添加@EnableCircuitBreaker或@SpringCloudApplication注解

我这边的springboot是2.4，springcloud是2020.0.0-M5，应该是版本太高造成的

pom.xml里添加

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>
或

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>
或

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>
会启动报错，如下：
java.lang.IllegalStateException: Annotation @EnableCircuitBreaker found,
 but there are no implementations. Did you forget to include a starter?

解决方法：

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
    <version>2.1.3.RELEASE</version>
</dependency>

参考：
https://blog.csdn.net/qq_24585103/article/details/103126411