public override void Invoke(AWSCredentials creds, RegionEndpoint region, int maxItems)
        {
            AmazonNeptuneConfig config = new AmazonNeptuneConfig();

            config.RegionEndpoint = region;
            ConfigureClient(config);
            AmazonNeptuneClient client = new AmazonNeptuneClient(creds, config);

            DescribeDBEngineVersionsResponse resp = new DescribeDBEngineVersionsResponse();

            do
            {
                DescribeDBEngineVersionsRequest req = new DescribeDBEngineVersionsRequest
                {
                    Marker = resp.Marker
                    ,
                    MaxRecords = maxItems
                };

                resp = client.DescribeDBEngineVersions(req);
                CheckError(resp.HttpStatusCode, "200");

                foreach (var obj in resp.DBEngineVersions)
                {
                    AddObject(obj);
                }
            }while (!string.IsNullOrEmpty(resp.Marker));
        }
        /// <summary>
        /// <para> Returns a list of the available DB engines. </para>
        /// </summary>
        ///
        /// <param name="describeDBEngineVersionsRequest">Container for the necessary parameters to execute the DescribeDBEngineVersions service method
        ///           on AmazonRDS.</param>
        ///
        /// <returns>The response from the DescribeDBEngineVersions service method, as returned by AmazonRDS.</returns>
        ///
        public DescribeDBEngineVersionsResponse DescribeDBEngineVersions(DescribeDBEngineVersionsRequest describeDBEngineVersionsRequest)
        {
            IRequest <DescribeDBEngineVersionsRequest> request  = new DescribeDBEngineVersionsRequestMarshaller().Marshall(describeDBEngineVersionsRequest);
            DescribeDBEngineVersionsResponse           response = Invoke <DescribeDBEngineVersionsRequest, DescribeDBEngineVersionsResponse> (request, this.signer, DescribeDBEngineVersionsResponseUnmarshaller.GetInstance());

            return(response);
        }