FeinClient服务实例缓存实时刷新

Spring Cloud OpenFeign默认会将从注册中心Consul获取的服务实例信息在Caffine缓存中缓存35秒，这会出现服务下线后，下线服务仍然被调用的问题，导致上游服务在缓存有效期内不可用。本文讲解如何通过Consul Watch机制来实时监听相关服务的更新，以实现服务的平滑上下线。

RoundRobinLoadBalancer使用CachingServiceInstanceListSupplierle加载服务实例信息

	public CachingServiceInstanceListSupplier(ServiceInstanceListSupplier delegate, CacheManager cacheManager) {
		super(delegate);
		this.serviceInstances = CacheFlux.lookup(key -> {
			// TODO: configurable cache name
            //首先从缓存中获取
			Cache cache = cacheManager.getCache(SERVICE_INSTANCE_CACHE_NAME);
			if (cache == null) {
				if (log.isErrorEnabled()) {
					log.error("Unable to find cache: " + SERVICE_INSTANCE_CACHE_NAME);
				}
				return Mono.empty();
			}
			List<ServiceInstance> list = cache.get(key, List.class);
			if (list == null || list.isEmpty()) {
				return Mono.empty();
			}
			return Flux.just(list).materialize