@Override
    public void initWithNiwsConfig(IClientConfig clientConfig) {
        ZoneAvoidancePredicate zonePredicate = new ZoneAvoidancePredicate(this, clientConfig);
        AvailabilityPredicate availabilityPredicate = new AvailabilityPredicate(this, clientConfig);
        compositePredicate = createCompositePredicate(zonePredicate, availabilityPredicate);
    }
A rule that uses the a {@link CompositePredicate} to filter servers based on zone and availability. The primary predicate is composed of
a {@link ZoneAvoidancePredicate} and {@link AvailabilityPredicate}, with the fallbacks to {@link AvailabilityPredicate}
and an "always true" predicate returned from {@link AbstractServerPredicate#alwaysTrue()} 

@author awang
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/ZoneAvoidanceRule.java