supplier.get().next().map(this::getInstanceResponse);

private final ConcurrentHashMap<Long, Integer> position;

 public Mono<Response<ServiceInstance>> choose(Request request) {
        // TODO: move supplier to Request?
        // Temporary conditional logic till deprecated members are removed.
        long threadId = Thread.currentThread().getId();
        if (serviceInstanceListSupplierProvider != null) {
            ServiceInstanceListSupplier supplier = serviceInstanceListSupplierProvider
                    .getIfAvailable(NoopServiceInstanceListSupplier::new);
            return supplier.get().next().map(serviceInstances -> getInstanceResponse(serviceInstances, threadId));
        }
        ServiceInstanceSupplier supplier = this.serviceInstanceSupplier
                .getIfAvailable(NoopServiceInstanceSupplier::new);
        return supplier.get().collectList().map(serviceInstances -> getInstanceResponse(serviceInstances, threadId));
    }

    private Response<ServiceInstance> getInstanceResponse(
            List<ServiceInstance> instances, long threadId) {
        if (instances.isEmpty()) {
            log.warn("No servers available for service: " + this.serviceId);
            return new EmptyResponse();
        }
        // TODO: enforce order?
        int pos = Math.abs(this.position.computeIfAbsent(threadId, k -> ThreadLocalRandom.current().nextInt(1000)));
        this.position.put(threadId, pos + 1);
        ServiceInstance instance = instances.get(pos % instances.size());
        return new DefaultResponse(instance);
    }