Optional<ZoneEndpoint> zoneEndpoint(ZoneId zone, ClusterSpec.Id cluster) {
        return Optional.ofNullable(zoneEndpoints.get(cluster))
                       .filter(__ -> deploysTo(zone.environment(), zone.region()))
                       .map(zoneEndpoints -> zoneEndpoints.get(zoneEndpoints.containsKey(zone) ? zone : null));
    }
Returns the zone endpoint specified for the given region, or empty.
config-model-api/src/main/java/com/yahoo/config/application/api/DeploymentInstanceSpec.java