@CheckReturnValue
    public HttpResponse getDelta(Iterable<String> regions) {
        return getApplications(APPS + "delta", requireNonNull(regions, "regions"));
    }
Retrieves the delta updates between the last fetch and the current one. See
https://github.com/Netflix/eureka/wiki/Understanding-eureka-client-server-communication#fetch-registry.
eureka/src/main/java/com/linecorp/armeria/internal/common/eureka/EurekaWebClient.java