When you have multiple instances of Microservices, having a traditional load balancer like F5, HAProxy becomes a single point of failure, if the load balancer fails. To prevent this we can use Ribbon for client-side load balancing.
Client-side load balancing involves having the client look up all of the service instances from Eureka and caching the physical locations locally on the client side. This way, when it notices a problem with any of the instances, it removes that instance from the local cache and prevents any future calls to that service instance.
Spring Cloud has built-in support for Ribbon. To turn it on, make sure you have fetchRegistry set to true like below, this tells client services to get physical locations of instances registered on Eureka and cache locally. For example, if service B is calling service A, do the following in service B.
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eureka: client: registerWithEureka: true fetchRegistry: true serviceUrl: defaultZone: http://localhost:8761/eureka/ instance: hostname: localhost |
Next, create a RestTemplate bean as shown below in your main application class.
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@LoadBalanced @Bean public RestTemplate restTemplate() { return new RestTemplate(); } |
Now, all you have to do is
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@Component public class RibbonClient { /*Because @LoadBalanced and @Bean exist in main app class, Spring automatically injects Ribbon enabled Rest template.*/ @Autowired RestTemplate restTemplate; @RequestMapping("/cotactserver") public String cotactserver() { String url = "http://SERVICEA/contact"; return restTemplate.getForObject(url, String.class); } } |
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