服務注冊是微服務架構中的關鍵組件，它允許應用程序動態發現和調用注冊的服務，而不是手動配置使用的服務。在這篇文中，我們將研究 Eureka 和 Spring Cloud Services 中的 Service Registry(基于 Eureka)。Eureka 來自 Netflix，有兩個組件 Eureka Server 和 Eureka Client。Eureka Server 可以使用@EnableEurekaServer注解嵌入到 Spring Boot 應用程序中，但在這里我們研究如何使用安裝了Spring Cloud CLI擴展的Spring Boot CLI來運行它。 該名單可以開始提供服務

spring cloud --list

spring cloud --list
configserver dataflow eureka h2 hystrixdashboard kafka stubrunner zipkin

通過跑步

spring cloud eureka

尤里卡將在 http://localhost:8761

我們customser-service和order-service這兩個Eureka ClientS式的customer-service調用order-service。

為了向這些服務注冊，Eureka Server我們需要包含以下依賴項：

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

該customer-service實施如下：

@SpringBootApplication
public class CustomerService {
    public static void main(String[] args) {
        SpringApplication.run(CustomerService.class, args);
    }
    @Configuration
    static class CustomerConfig {
        @Bean
        @LoadBalanced
        public RestTemplate restTemplate() {
            return new RestTemplate();
        }
    }
    @RestController
    @Slf4j
    static class CustomerController {
        private static final String TEMPLATE = UriComponentsBuilder.fromUriString("http://order-service/orders")
                .queryParam("customerId", "{customerId}").build().toUriString();
        private final RestTemplate restTemplate;
        private final CustomerRepository customerRepository;
        public CustomerController(RestTemplate restTemplate, CustomerRepository customerRepository) {
            this.restTemplate = restTemplate;
            this.customerRepository = customerRepository;
        }
        @GetMapping("/customers/{id}")
        public ResponseEntity<Customer> getCustomer(@PathVariable Long id) {
            log.info("getCustomer with id {}", id);
            Customer customer = customerRepository.getCustomer(id);
            if (customer == null) {
                return new ResponseEntity<>(HttpStatus.NOT_FOUND);
            }
            Order order = restTemplate.getForObject(TEMPLATE, Order.class, id);
            if (order != null) {
                customer.setOrder(new Order(order.getDetails(), order.getTime()));
            }
            return new ResponseEntity<>(customer, HttpStatus.OK);
        }
    }
    @Data
    @AllArgsConstructor
    static class Customer {
        Long id;
        String name;
        Order order;
    }
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    static class Order {
        String details;
        LocalDateTime time;
    }
}

我們不再需要@EnableDiscoveryClient注解，當DiscoveryClient實現(如本文中使用的Spring Cloud Netflix Eureka)在類路徑上可用時，Spring Boot 應用程序將自己注冊到服務注冊中心。(更多詳情請見EurekaClientAutoConfiguration)

默認情況下，Spring Boot 應用程序會自動注冊自己。有一個方便的/service-registry執行器端點，以便查詢和注??冊/取消注冊服務注冊表

在我們的示例中，如果我們想order-service停止服務，我們可以使用：

echo '{"status":"OUT_OF_SERVICE"}' | http post :8081/actuator/service-registry

在此之后，customer-service將能夠調用order-service大約 30 秒，因為這是Eureka Clients 查找注冊表信息以定位其服務并進行遠程調用的默認設置。

將RestTemplate不再通過自動配置創建的，在customer-service我們需要創建一個。我們使用@LoadBalanced注釋來確保它在order-service實例之間進行負載平衡。

使用 Feign

另一種調用下游服務的方法是使用Feign，它為我們提供了一個類型安全的 HTTP 客戶端。

@SpringBootApplication
@EnableFeignClients
public class CustomerServiceFeign {
    public static void main(String[] args) {
        SpringApplication.run(CustomerServiceFeign.class, args);
    }
    @RestController
    @Slf4j
    static class CustomerController {
        private final OrderServiceClient orderServiceClient;
        private final CustomerRepository customerRepository;
        public CustomerController(OrderServiceClient orderServiceClient, CustomerRepository customerRepository) {
            this.orderServiceClient = orderServiceClient;
            this.customerRepository = customerRepository;
        }
        @GetMapping("/customers/{id}")
        public ResponseEntity<Customer> getCustomer(@PathVariable Long id) {
            log.info("getCustomer with id {}", id);
            Customer customer = customerRepository.getCustomer(id);
            if (customer == null) {
                return new ResponseEntity<>(HttpStatus.NOT_FOUND);
            }
            Order order = orderServiceClient.getOrder(id);
            if (order != null) {
                customer.setOrder(order.getDetails());
            }
            return new ResponseEntity<>(customer, HttpStatus.OK);
        }
    }
    @FeignClient("order-service")
    interface OrderServiceClient {
        @GetMapping("/orders")
        Order getOrder(@RequestParam("customerId") Long id);
    }   
}

使用@FeignClient接口上的注釋，實際實現是在運行時提供的。在后臺創建了一個功能區負載平衡器。

Spring Boot 管理員

Spring Boot Admin是管理 Spring Boot 微服務的絕佳工具。不幸的是，Spring Boot / Spring Cloud CLI 尚不支持它，但我們可以輕松設置 Spring Boot 管理服務器。創建 Spring Boot 應用程序后，我們需要包含以下依賴項：

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-security</artifactId>
    </dependency>
    <dependency>
        <groupId>de.codecentric</groupId>
        <artifactId>spring-boot-admin-starter-server</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    </dependency>
    <dependency>
       <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

和

@SpringBootApplication
@EnableAdminServer
public class SpringBootAdmin {
    public static void main(String[] args) {
        SpringApplication.run(SpringBootAdmin.class, args);
    }
    @Configuration
    static class WebSecurityConfig extends WebSecurityConfigurerAdapter {
        private final String adminContextPath;
        public WebSecurityConfig(AdminServerProperties adminServerProperties) {
            this.adminContextPath = adminServerProperties.getContextPath();
        }
        @Override
        protected void configure(HttpSecurity http) throws Exception {
            SavedRequestAwareAuthenticationSuccessHandler successHandler = new SavedRequestAwareAuthenticationSuccessHandler();
            successHandler.setDefaultTargetUrl(adminContextPath + "/");
            successHandler.setTargetUrlParameter("redirectTo");
            http.authorizeRequests()
                    .antMatchers(adminContextPath + "/assets/**").permitAll()
                    .antMatchers(adminContextPath + "/login").permitAll()
                    .anyRequest().authenticated()
                    .and()
                    .formLogin().loginPage(adminContextPath + "/login").successHandler(successHandler).and()
                    .logout().logoutUrl(adminContextPath + "/logout").and()
                    .httpBasic().and()
                    .csrf().disable();
        }
    }
}

Pivotal Cloud Foundry (PCF) 上的服務注冊表

到現在為止還挺好。讓我們在Pivotal Web 服務(由 Pivotal 托管的 PCF 實例)上設置這個小示例，我們將在其中使用Spring Cloud Services的 Service Registry 服務(trial計劃)

首先，我們需要安裝CloudFoundry CLI并創建一個Pivotal Web Services帳戶。

我們創建一個service-registry使用以下命令命名的服務實例

cf cs p-service-registry trial service-registry

然后我們需要將以下依賴項包含到Eureka Client應用程序中 ( customer-service, customer-service-feign, order-service, spring-boot-admin)

<dependency>
    <groupId>io.pivotal.spring.cloud</groupId>
    <artifactId>spring-cloud-services-starter-service-registry</artifactId>
</dependency>

manifest.yml為所有服務創建文件很方便。因為customer-service是

applications:
- name: customer-service
  memory: 756M
  instances: 1
  path: target/customer-service.jar
  buildpack: java_buildpack
  services:
  - service-registry

在構建應用程序后，mvn clean package我們可以部署

cf push --random-route

部署完所有服務后，我們應該會看到如下內容：

cf apps
name                     requested state   instances   memory   disk   urls
customer-service         started           1/1         756M     1G     customer-service-shy-mandrill.cfapps.io
customer-service-feign   started           1/1         756M     1G     customer-service-feign-cheerful-hartebeest.cfapps.io
order-service            started           1/1         756M     1G     order-service-appreciative-koala.cfapps.io
spring-boot-admin        started           1/1         756M     1G     spring-boot-admin-anxious-leopard.cfapps.io

我們可以測試服務：

http customer-service-shy-mandrill.cfapps.io/customers/1

{
    "id": 1,
    "name": "Paul Molive",
    "order": {
        "details": "Grilled Chicken Sandwich",
        "time": "2018-08-10T07:32:38.463"
    }
}

和 Spring Boot 管理控制臺可用：

在環境變量中設置密碼的好習慣。在 Spring Boot Admin 中，我們使用了以下內容：

spring:
  security:
    user:
      name: admin
      password: ${ADMIN_PASSWORD:admin}

我們在 Pivotal Cloud Foundry的空間中ADMIN_PASSWORD為spring-boot-admin應用程序設置了development

cf set-env spring-boot-admin admin s3cr3t

當customer-service綁定到service-registry服務實例時，在VCAP_SERVICES環境變量中設置了連接詳細信息。

cf env customer-service

{
 "VCAP_SERVICES": {
  "p-service-registry": [
   {
    "binding_name": null,
    "credentials": {
     "access_token_uri": "https://p-spring-cloud-services.uaa.run.pivotal.io/oauth/token",
     "client_id": "p-service-registry-f31ae316-8f1c-4a2d-84ab-02062a0c5aae",
     "client_secret": "ygjAdaV6Gnff",
     "uri": "https://eureka-aa041440-7a75-45b8-bbba-435c79e4ff66.cfapps.io"
    },
    "instance_name": "service-registry",
    "label": "p-service-registry",
    "name": "service-registry",
    "plan": "trial",
    "provider": null,
    "syslog_drain_url": null,
    "tags": [
     "eureka",
     "discovery",
     "registry",
     "spring-cloud"
    ],
    "volume_mounts": []
   }
  ]
 }
}

由于我們沒有配置eureka.client.service-url.defaultZone它，它是如何從VCAP_SERVICES? 包含在EurekaServiceConnector提供eureka.client.*屬性的 中，該屬性EurekaServiceInfo封裝了如何訪問service-registry服務的信息。