Sticky session loadbalancing in spring Microservices

Question

I am new to Spring and trying to do a proof-of-concept on the sticky session loadbalancing (I am using Eureka for service discovery, Spring Cloud Gateway and Spring Cloud Loadbalancer, its working in round-robin fashion now). I am unable to achieve on sticky session lb. Can some one please help me in this or share code (for sticky session loadbalancer) which I can see and learn.

Answer 1

By default, Spring Cloud Loadbalancer (see config here) uses round-robin load balancing.

To change this, in your Spring Cloud Gateway, use RequestBasedStickySessionServiceInstanceListSupplier.

By setting the application context (bootstrap.yml):

spring.cloud.loadbalancer.configurations: request-based-sticky-session

or create a bean:

public class CustomLoadBalancerConfiguration {

    @Bean
    public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(
            ConfigurableApplicationContext context) {
        return ServiceInstanceListSupplier.builder()
                    .withDiscoveryClient()
                    .withRequestBasedStickySession()
                    .build(context);
        }
    }
}

Spring Documentation

• https://docs.spring.io/spring-cloud-commons/docs/current/reference/html/#request-based-sticky-session-for-loadbalancer Note: Take care of cookie handling.

Medium article with related technologies (Eureka, Spring Cloud Gateway) and complete boilerplate code:

• https://progen.medium.com/load-balancing-spring-cloud-applications-using-eureka-and-spring-cloud-gateway-43d0bcf57cc3
• https://github.com/negorp/spring_load_balancing

CAVEAT

If you HAVE to use stick-load balancing, I would encourage you to understand why this is the case. Please investigate why you need to use it and ideally adapt your application to that it is not dependent on the request being passed to the same server. Please read the following for reasons to NOT use them:

• https://dev.to/gkoniaris/why-you-should-never-use-sticky-sessions-2pkj
• Sticky Sessions: Good or Bad?

Generally, I would say that having to use sticky sessions in indicative of a sub-optimal architecture.