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

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

            DescribeDBParameterGroupsResponse resp = new DescribeDBParameterGroupsResponse();

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

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

                foreach (var obj in resp.DBParameterGroups)
                {
                    AddObject(obj);
                }
            }while (!string.IsNullOrEmpty(resp.Marker));
        }