Make DelegatingServiceInstanceListSupplier implement SelectedInstanceCallback

I've tried to setup a custom load balancer as described in this post. However, with spring-cloud-starter-loadbalancer:3.1.4 I'm experiencing

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier' available: more than one 'primary' bean found among candidates: [CustomServiceInstanceListSupplier, retryAwareDiscoveryClientServiceInstanceListSupplier]

@Configuration
@LoadBalancerClient(value = "custom", configuration = CustomLoadBalancerConfiguration.class)
public class CustomLoadBalancerClient {
}

public class CustomLoadBalancerConfiguration {

	@Bean
	@Primary
	public ServiceInstanceListSupplier customServiceInstanceListSupplier(ConfigurableApplicationContext context, RedissonClient redissonClient) {
		ServiceInstanceListSupplier delegate = ServiceInstanceListSupplier.builder()
				.withDiscoveryClient()
				.withCaching()
				.build(context);
		return new CustomServiceInstanceListSupplier(delegate, redissonClient);
	}
}

public class CustomServiceInstanceListSupplier extends DelegatingServiceInstanceListSupplier implements SelectedInstanceCallback {
...
}

When deploying the application to Kubernetes along spring-cloud-kubernetes-facric8-loadbalancer:2.1.4 and activating spring.cloud.kubernetes.loadbalancer.mode=SERVICE it's even getting worse

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier' available: more than one 'primary' bean found among candidates: [customServiceInstanceListSupplier, kubernetesServicesListSupplier, retryAwareDiscoveryClientServiceInstanceListSupplier]

Am I doing something wrong, or is the example from the post wrong?

Removing @Primary leads to

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier' available: expected single matching bean but found 2: customServiceInstanceListSupplier,kubernetesServicesListSupplier

Further debugging revealed a second issue. My CustomServiceInstanceListSupplier implements SelectedInstanceCallback which the RoundRobinLoadBalancer respects by calling SelectedInstanceCallback#selectedServiceInstance

public class RoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalancer {
...
private Response<ServiceInstance> processInstanceResponse(ServiceInstanceListSupplier supplier,
			List<ServiceInstance> serviceInstances) {
		Response<ServiceInstance> serviceInstanceResponse = getInstanceResponse(serviceInstances);
		if (supplier instanceof SelectedInstanceCallback && serviceInstanceResponse.hasServer()) {
			((SelectedInstanceCallback) supplier).selectedServiceInstance(serviceInstanceResponse.getServer());
		}
		return serviceInstanceResponse;
	}
}

However, with Spring retry on the classpath my CustomServiceInstanceListSupplier is wrapped in a RetryAwareServiceInstanceListSupplier which is not respecting SelectedInstanceCallback on its delegate.

@Configuration(proxyBeanMethods = false)
	@ConditionalOnBlockingDiscoveryEnabled
	@ConditionalOnClass(RetryTemplate.class)
	@Conditional(BlockingOnAvoidPreviousInstanceAndRetryEnabledCondition.class)
	@AutoConfigureAfter(BlockingSupportConfiguration.class)
	@ConditionalOnBean(ServiceInstanceListSupplier.class)
	public static class BlockingRetryConfiguration {

		@Bean
		@ConditionalOnBean(DiscoveryClient.class)
		@Primary
		public ServiceInstanceListSupplier retryAwareDiscoveryClientServiceInstanceListSupplier(
				ServiceInstanceListSupplier delegate) {
			return new RetryAwareServiceInstanceListSupplier(delegate);
		}

	}

I suspect that every implementation of ServiceInstanceListSupplier using some sort of "delegate" has the same problem, see RequestBasedStickySessionServiceInstanceListSupplier as an example.

@OlgaMaciaszek

@OlgaMaciaszek any feedback appreciated as I'm stuck here. What I need to achieve is that my own ServiceInstanceListSupplier is used regardless of any auto-configured supplier. Or I need a way to use the auto-configured one as a delegate in my supplier, but that won't work as retryAwareDiscoveryClientServiceInstanceListSupplier is marked @Primary.

@spencergibb

@spencergibb Can you please have a look and give me hint if this is considered a bug or if any configuration possibility exists as a workaround? I've tried using @AutoConfigureAfter(LoadBalancerClientConfiguration.ReactiveRetryConfiguration.class) at my class annotated with @LoadBalancerClient without a chance. retryAwareDiscoveryClientServiceInstanceListSupplier is still configured after mine ...

@HJK181

Hello, @HJK181. This is happening as for retrying failed requests, RetryAwareServiceInstanceListSupplier is enabled by default. As indicated in the docs, if you do not want it to be instantiated, you should set spring.cloud.loadbalancer.retry.avoidPreviousInstance to false. Does this solve your issue?

I’d like to use the retry functionality, but in conjunction with my custom instance list supplier.

That property does not disable retry. It only disables the RetryAwareServiceInstanceListSupplier that handles avoiding retrying on the same instance.

I can check tomorrow if I find the time to setup my IDE for contributing to the project. Is there any chance that it will be backported to 3.1.x?

Unfortunately, not really. We mostly only backport bugfixes. This would be a new feature.

Fix DelegatingServiceInstanceListSupplier must

@OlgaMaciaszek

@OlgaMaciaszek #1226 FYI

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