Feign Service Consumer Implementation

Feign is a declarative web service client that simplifies HTTP API development. It uses annotations to define service interfaces and integrates seamlessly with Spring MVC.

Environment Setup

Required Components:

• Java 8+
• Spring Boot 2.1.1+
• Spring Cloud Finchley+

Dependencies:

<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-openfeign</artifactId>
    </dependency>
</dependencies>

Service Registry Configuration

application.properties:

spring.application.name=feign-service-registry
server.port=8001
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false
eureka.client.serviceUrl.defaultZone=http://localhost:8001/eureka/

Registry Server Class:

@EnableEurekaServer
@SpringBootApplication
public class ServiceRegistryApplication {
    public static void main(String[] args) {
        SpringApplication.run(ServiceRegistryApplication.class, args);
    }
}

Feign Client Implementation

Consumer Configuration:

spring.application.name=feign-service-consumer
server.port=9002
eureka.client.serviceUrl.defaultZone=http://localhost:8001/eureka/

Consumer Application Class:

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class FeignConsumerApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignConsumerApplication.class, args);
    }
}

Feign Client Interface:

@FeignClient(name = "target-service-provider")
public interface ServiceProxy {
    @RequestMapping(value = "/greet")
    String sendGreeting(@RequestParam(value = "user") String user);
}

Consumer Controller:

@RestController
public class ConsumerEndpoint {
    @Autowired
    ServiceProxy serviceProxy;
    
    @RequestMapping("/greet/{user}")
    public String forwardGreeting(@PathVariable("user") String user) {
        return serviceProxy.sendGreeting(user);
    }
}

Target Service Implementation

Target Service Configuration:

spring.application.name=target-service-provider
server.port=9003
eureka.client.serviceUrl.defaultZone=http://localhost:8001/eureka/

Target Service Controller:

@RestController
public class ServiceEndpoint {
    @RequestMapping("/greet")
    public String handleGreeting(@RequestParam String user) {
        return user + ", Welcome!";
    }
}

Ribbon Load Balancer Implementation

Ribbon provides client-side load balancing with configurable algorithms and connection management.

Dependencies:

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

Load Balanced Client Setup

Consumer Configuration:

spring.application.name=ribbon-loadbalancer
server.port=9006
eureka.client.serviceUrl.defaultZone=http://localhost:8003/eureka/

Service Provider Configurations:

# Provider 1
spring.application.name=balanced-service
server.port=9007

# Provider 2
spring.application.name=balanced-service
server.port=9008

Load Balanced Client Application:

@SpringBootApplication
@EnableDiscoveryClient
public class RibbonClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(RibbonClientApplication.class, args);
    }
    
    @Bean
    @LoadBalanced
    public RestTemplate balancedRestTemplate() {
        return new RestTemplate();
    }
}

Client Controller with Load Balancing:

@RestController
public class LoadBalancedController {
    @Autowired
    RestTemplate restTemplate;
    
    @RequestMapping("/invoke")
    public String callService() {
        return restTemplate.getForObject(
            "http://balanced-service/greet?name=developer", 
            String.class
        );
    }
}

Load Balancing Strategies

Ribbon supports multiple load balancing algorithms:

Custom Strategy Configuartion:

Method 1 - Properties file:

balanced-service.ribbon.NFLoadBalancerRuleClassName=com.netflix.loadbalancer.RandomRule

Method 2 - Configuration class:

@Configuration
public class CustomRibbonConfig {
    @Bean
    public IRule customRule() {
        return new RandomRule();
    }
}

@RibbonClient(
    name = "balanced-service", 
    configuration = CustomRibbonConfig.class
)
public class ServiceConfiguration {
}

Manual Server List Configuration:

balanced-service.ribbon.listOfServers=localhost:9007,localhost:9008

Feign with Ribbon Integration

Feign automatically integrates with Ribbon for load balancing when multiple instances of the same service are registered.

Enhanced Feign Client with Load Balancing:

@FeignClient(name = "balanced-service")
public interface LoadBalancedProxy {
    @RequestMapping(value = "/greet")
    String distributedGreeting(@RequestParam(value = "name") String name);
}

Enhanced Controller:

@RestController
public class EnhancedController {
    @Autowired
    LoadBalancedProxy loadBalancedProxy;
    
    @RequestMapping("/distributed/{name}")
    public String loadBalancedCall(@PathVariable("name") String name) {
        return loadBalancedProxy.distributedGreeting(name);
    }
}