如何解决Netflix Eureka服务发现中的‘unknown-host’错误？

我正在跟随教程用Eureka实现服务发现，从start.spring.io下载了包含Eureka服务器和两个客户端的Spring项目。Eureka服务器的Web界面已经识别到两个服务，但通过服务名发送GET请求时出现unknown-host错误。已经尝试了Stack Overflow相关文章里的所有方法，都没用。

以下是我的配置：

Eureka服务器代码 #

@SpringBootApplication
@EnableEurekaServer
public class DiscoveryServerApplication {

    public static void main(String[] args) {
        SpringApplication.run(DiscoveryServerApplication.class, args);
    }

}

Eureka服务器pom.xml #

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.12</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>io.javabrains</groupId>
    <artifactId>discovery-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>discovery-server</name>
    <description>Discovery Server</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>2021.0.7</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

Eureka服务器application.properties #

server.port=8761
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

movie-service-catalog的pom.xml #

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.12</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>2021.0.7</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-parent</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

movie-service-catalog的application.properties #

spring.application.name=movie-catalog-service
server.port=8081

movie-service-catalog代码 #

@SpringBootApplication
@EnableEurekaClient
public class MovieCatalogServiceApplication {

    @Bean
    @LoadBalanced
    public RestTemplate getRestTemplate(){
        return new RestTemplate();
    }


    public static void main(String[] args) {
        SpringApplication.run(MovieCatalogServiceApplication.class, args);
    }

}

@RestController
@RequestMapping("/catalog")
public class MovieCatalogResource {

    @Autowired
    private RestTemplate restTemplate;



    @RequestMapping("/{userId}")
    public List<CatalogItem> getCatalog(@PathVariable String userId){

        RestTemplate restTemplate = new RestTemplate();
        //get all rated movie IDs, movies user watched
        UserRating ratings = restTemplate.getForObject("http://ratings-data-service/ratingsdata/users/" + userId, UserRating.class);

        return ratings.getUserRating().stream().map(rating -> {
            //For each movie ID, call movie info service and details
            Movie movie = restTemplate.getForObject("http://movie-info-service/movies/" + rating.getMovieId(), Movie.class);
            //put them together
            return new CatalogItem(movie.getName(), "Test", rating.getRatings());
                }
        ).collect(Collectors.toList());



    }
}

ratings-data-service的配置与movie-catalog-service相同

解决方案 #

问题核心是你在getCatalog方法里重新创建了RestTemplate实例，没有使用Spring容器中带有@LoadBalanced注解的那个。

@LoadBalanced注解会为RestTemplate注入服务发现和负载均衡能力，使其能将服务名解析为对应的实例地址。但你新new的RestTemplate没有被Spring增强，自然无法识别Eureka中的服务名。

修改步骤：

1. 删除方法内的RestTemplate restTemplate = new RestTemplate();代码，直接使用Autowired注入的实例：

@RequestMapping("/{userId}")
public List<CatalogItem> getCatalog(@PathVariable String userId){
    UserRating ratings = restTemplate.getForObject("http://ratings-data-service/ratingsdata/users/" + userId, UserRating.class);

    return ratings.getUserRating().stream().map(rating -> {
        Movie movie = restTemplate.getForObject("http://movie-info-service/movies/" + rating.getMovieId(), Movie.class);
        return new CatalogItem(movie.getName(), "Test", rating.getRatings());
            }
    ).collect(Collectors.toList());
}

2. 建议在客户端的application.properties中显式配置Eureka服务器地址（默认会连localhost:8761，但显式配置更稳妥）：

eureka.client.service-url.defaultZone=http://localhost:8761/eureka/

重启服务后，即可正常通过服务名调用接口。

内容的提问来源于stack exchange，提问作者Gurmukh Singh