Q. Is there any reason why does LoadBalancerCacheManager Bean excluded from autowire candidates?

[kworkbee]

Hi, I'm planning to implement a new feature so that LoadBalancer can switch to another zone if all instances within a particular zone fail to respond.

For acheiving this, the new ServiceInstanceListSupplier needs cache, which is why I wanted to inject LoadBalancerCacheManager.

I checked that the Bean is currently excluded from Autowire Candidates, and I wonder if there is a reason why it was written like this.

I wonder if it is okay to exclude that option to achieve what I intend, or if not, what other alternatives can be used.

[OlgaMaciaszek]

I'm not sure what you mean by it being excluded from Autowire Candidates. The caching should work out of the box. If you're experiencing any issues with it, please provide a minimal, complete, verifiable example that reproduces the issue.

[kworkbee]

@OlgaMaciaszek

In LoadBalancerCacheAutoConfiguration, LoadBalancerCacheManager beans seem to be registered excluded from the autowire candidates.

        @Configuration(proxyBeanMethods = false)
	@ConditionalOnClass({ Caffeine.class, CaffeineCacheManager.class })
	protected static class CaffeineLoadBalancerCacheManagerConfiguration {

                // Here
		@Bean(autowireCandidate = false)
		@ConditionalOnMissingBean
		LoadBalancerCacheManager caffeineLoadBalancerCacheManager(LoadBalancerCacheProperties cacheProperties) {
			return new CaffeineBasedLoadBalancerCacheManager(cacheProperties);
		}

	}

	@Configuration(proxyBeanMethods = false)
	@Conditional(OnCaffeineCacheMissingCondition.class)
	@ConditionalOnClass(ConcurrentMapWithTimedEviction.class)
	protected static class DefaultLoadBalancerCacheManagerConfiguration {

                // Here
		@Bean(autowireCandidate = false)
		@ConditionalOnMissingBean
		LoadBalancerCacheManager defaultLoadBalancerCacheManager(LoadBalancerCacheProperties cacheProperties) {
			return new DefaultLoadBalancerCacheManager(cacheProperties);
		}

	}

Because of this configuration, the newly registered Bean cannot be injected with LoadBalancerCacheManager.

        @Bean
	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "zone-failover-awareness")
        // LoadBalancerCacheManager cannot be injected
	LoadBalancerCacheDataManager zoneFailoverAwarenessLoadBalancerCacheManager(LoadBalancerCacheManager cacheManager) {
		return new ZoneFailoverAwarenessLoadBalancerCacheDataManager(cacheManager);
	}

If I include beans excluded from the autowire candidates again, the existing tests below will fail.

spring-cloud-commons/spring-cloud-loadbalancer/src/test/java/org/springframework/cloud/loadbalancer/config/LoadBalancerCacheAutoConfigurationTests.java

Lines 130 to 171 in e4bd5b3

	@Test
	void defaultLoadBalancerCacheShouldNotOverrideCacheTypeSetting() {
	ApplicationContextRunner contextRunner = noCaffeineRunner().withUserConfiguration(TestConfiguration.class)
	.withPropertyValues("spring.cache.type=none");
	contextRunner.run(context -> {
	assertThat(context.getBeansOfType(CacheManager.class)).hasSize(2);
	assertThat(context.getBean("defaultLoadBalancerCacheManager"))
	.isInstanceOf(DefaultLoadBalancerCacheManager.class);
	assertThat(context.getBeansOfType(CacheManager.class).get("cacheManager"))
	.isInstanceOf(NoOpCacheManager.class);
	});
	}
	@Test
	void defaultLoadBalancerCacheShouldNotOverrideExistingCacheManager() {
	ApplicationContextRunner contextRunner = noCaffeineRunner().withUserConfiguration(TestConfiguration.class);
	contextRunner.run(context -> {
	assertThat(context.getBeansOfType(CacheManager.class)).hasSize(2);
	assertThat(context.getBean("cacheManager")).isInstanceOf(ConcurrentMapCacheManager.class);
	assertThat(((CacheManager) context.getBean("cacheManager")).getCacheNames()).isEmpty();
	assertThat(((CacheManager) context.getBean("defaultLoadBalancerCacheManager")).getCacheNames()).hasSize(1);
	assertThat(((CacheManager) context.getBean("defaultLoadBalancerCacheManager")).getCacheNames())
	.contains("CachingServiceInstanceListSupplierCache");
	});
	}
	@Test
	void shouldNotInstantiateDefaultLoadBalancerCacheIfDisabled() {
	ApplicationContextRunner contextRunner = noCaffeineRunner()
	.withPropertyValues("spring.cloud.loadbalancer.cache.enabled=false")
	.withUserConfiguration(TestConfiguration.class);
	contextRunner.run(context -> {
	assertThat(context.getBeansOfType(CacheManager.class)).hasSize(1);
	assertThat(context.getBean("cacheManager")).isInstanceOf(ConcurrentMapCacheManager.class);
	assertThat(((CacheManager) context.getBean("cacheManager")).getCacheNames()).isEmpty();
	});
	}

[OlgaMaciaszek]

These tests exactly show why this is done - so that the LoadBalancerCache does not override cache managers configured by users or taken up from other autoconfigurations.