@VisibleForTesting
    void onUpdate(List<Server> oldList, List<Server> newList) {
        Set<Server> oldSet = new HashSet<>(oldList);
        Set<Server> newSet = new HashSet<>(newList);
        List<DiscoveryResult> discoveryResults = Sets.difference(oldSet, newSet).stream()
                .map(server ->
                        new DiscoveryResult((DiscoveryEnabledServer) server, loadBalancer.getLoadBalancerStats()))
                .collect(Collectors.toList());
        listener.onChange(discoveryResults);
    }
@author Argha C
@since 2/25/21
<p>
Implements a resolver, wrapping a ribbon load-balancer.
zuul-discovery/src/main/java/com/netflix/zuul/discovery/DynamicServerResolver.java