/// <summary>
        /// Adds new instances to the load balancer.
        /// Once the instance is registered, it starts receiving traffic and requests from the load balancer.
        /// Any instance that is not in any of the Availability Zones registered for the load balancer will be moved to the OutOfService state.
        /// It will move to the InService state when the Availability Zone is added to the load balancer.
        /// </summary>
        /// <param name="loadBalancer">The name associated with the load balancer.</param>
        /// <param name="instances">A list of instance IDs that should be registered with the load balancer.</param>
        /// <param name="settings">The <see cref="LoadBalancingSettings"/> used during the request to AWS.</param>
        /// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive notice of cancellation.</param>
        public async Task <bool> RegisterInstances(string loadBalancer, IList <string> instances, LoadBalancingSettings settings, CancellationToken cancellationToken = default(CancellationToken))
        {
            if (String.IsNullOrEmpty(loadBalancer))
            {
                throw new ArgumentNullException("loadBalancer");
            }
            if ((instances == null) || (instances.Count == 0))
            {
                throw new ArgumentNullException("instances");
            }



            //Create Request
            AmazonElasticLoadBalancingClient         client  = this.CreateClient(settings);
            RegisterInstancesWithLoadBalancerRequest request = new RegisterInstancesWithLoadBalancerRequest();

            request.LoadBalancerName = loadBalancer;

            foreach (string instance in instances)
            {
                request.Instances.Add(new Instance(instance));
            }



            //Check Response
            RegisterInstancesWithLoadBalancerResponse response = await client.RegisterInstancesWithLoadBalancerAsync(request, cancellationToken);

            if (response.HttpStatusCode == HttpStatusCode.OK)
            {
                _Log.Verbose("Successfully registered instances '{0}'", string.Join(",", instances));
                return(true);
            }
            else
            {
                _Log.Error("Failed to register instances '{0}'", string.Join(",", instances));
                return(false);
            }
        }