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I have the following configuration for request-based sticky session using Spring Cloud LoadBalancer

spring:
  cloud:
    discovery.client.simple.instances:
      say-hello:
        - instanceId: say-hello1
          uri: http://localhost:8080
        - instanceId: say-hello2
          uri: http://localhost:8081

    loadbalancer:
      configurations: request-based-sticky-session
      sticky-session:
        add-service-instance-cookie: true

server.port:9090

the following call:

$ http :9090/hi 'Cookie:sc-lb-instance-id=say-hello1'

should go only to the say-hello1 instance based on the Request-based Sticky Session for LoadBalancer but instead is using round robin load balancing.

What do I miss here?

Here is the source code to try it: https://github.com/altfatterz/client-side-loadbalancing

Zoltan Altfatter
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1 Answers1

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There are 2 things to consider here:

  1. In the sample, the cookie has to be passed on to the actual load-balanced request, for example like so:

    @GetMapping("/hi")
public String hi(@RequestParam(value = "name", defaultValue = "Mary") String name) {
 logger.info("Accessing /hi endpoint");
 HttpHeaders headers = new HttpHeaders();
 headers.set("Cookie", "sc-lb-instance-id=say-hello1");

 HttpEntity entity = new HttpEntity(headers);
 ResponseEntity<String> greeting = restTemplate.exchange("http://say-hello/greeting", HttpMethod.GET, entity, String.class, new HashMap<>());
 return greeting + " " + name;
}

  2. This feature is only supported for WebClient-backed load-balancing. It was not properly documented. I have documented it here. I have also created a GitHub issue for adding the non-reactive implementation, however, the decision to implement it will be dependant on larger community interest.

OlgaMaciaszek
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  • Thanks Olga! Is there a way to check what ServiceInstance a RestTemplate based load balancer client chose for a request? – Zoltan Altfatter Jun 18 '21 at 20:21
  • We log that. Also we provide `LoadBalancerLifecycle` interface (https://docs.spring.io/spring-cloud-commons/docs/current/reference/html/#loadbalancer-lifecycle) - you can provide your own logic and add that information to your final response. – OlgaMaciaszek Jun 21 '21 at 09:24