Custom resource support for .NET Core Lambda functions

Cloudformation.template

...
    "LambdaGetLatestAMI": {
      "Type": "AWS::CloudFormation::CustomResource",
      "Properties": {
        "ServiceToken": "arn:aws:lambda:eu-west-1:123456789012:function:dev-ops-stack-GetLatestAMIAsync-4N4U4OD0C8M3",
        "Region": { "Ref": "AWS::Region" }
      }
    },
...

CloudFormationModels.cs

using Amazon.Lambda.Core;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;

namespace DevOpsLambdas
{
    public class CloudFormationRequest
    {
        public string StackId { get; set; }
        public string ResponseURL { get; set; }
        public string RequestType { get; set; }
        public string ResourceType { get; set; }
        public string RequestId { get; set; }
        public string LogicalResourceId { get; set; }
    }

    public class CloudFormationResponse
    {
        public string Status { get; set; }
        public string Reason { get; set; }
        public string PhysicalResourceId { get; set; }
        public string StackId { get; set; }
        public string RequestId { get; set; }
        public string LogicalResourceId { get; set; }
        public object Data { get; set; }

        public static async Task<CloudFormationResponse> CompleteCloudFormationResponse(object data, CloudFormationRequest request, ILambdaContext context)
        {
            var responseBody = new CloudFormationResponse
            {
                Status = data is Exception ? "FAILED" : "SUCCESS",
                Reason = "See the details in CloudWatch Log Stream: " + context.LogStreamName,
                PhysicalResourceId = context.LogStreamName,
                StackId = request.StackId,
                RequestId = request.RequestId,
                LogicalResourceId = request.LogicalResourceId,
                Data = data
            };

            try
            {
                HttpClient client = new HttpClient(new LoggingHandler(new HttpClientHandler()));

                var jsonContent = new StringContent(JsonConvert.SerializeObject(responseBody));
                jsonContent.Headers.Remove("Content-Type");

                var postResponse = await client.PutAsync(request.ResponseURL, jsonContent);

                postResponse.EnsureSuccessStatusCode();
            }
            catch (Exception ex)
            {
                LambdaLogger.Log("Exception: " + ex.ToString());

                responseBody.Status = "FAILED";
                responseBody.Data = ex;
            }

            return responseBody;
        }
    }
}

SampleFunction.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Threading.Tasks;

using Amazon.Lambda.Core;

using Amazon;
using Amazon.EC2;

using Newtonsoft.Json;
using Amazon.EC2.Model;
using System.Net.Http;
using System.Text;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.
[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.Json.JsonSerializer))]

namespace DevOpsLambdas
{
    public class Functions
    {
        public async Task<CloudFormationResponse> GetLatestAMIAsync(GetLatestAMIRequest request, ILambdaContext context)
        {
            LambdaLogger.Log("GetLatestAMIAsync invoked: " + JsonConvert.SerializeObject(request));

            if (request.RequestType != "Delete")
            {
                var client = new AmazonEC2Client(RegionEndpoint.GetBySystemName(request.ResourceProperties.Region));
                var images = await client.DescribeImagesAsync(new DescribeImagesRequest()
                {
                    Filters = new List<Filter> { new Filter("name", new List<string>() { "Windows_Server-2016-English-Full-Base-*" }) },
                    Owners = new List<string>() { "amazon" }
                });

                var latestImage = images.Images.OrderByDescending(i => i.CreationDate).Take(1).FirstOrDefault();
                string imageId = latestImage.ImageId;

                return await CloudFormationResponse.CompleteCloudFormationResponse(new { ImageId = imageId }, request, context);
            }

            return await CloudFormationResponse.CompleteCloudFormationResponse(null, request, context);
        }
    }
}

SampleModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace DevOpsLambdas
{
    public class GetLatestAMIRequest : CloudFormationRequest
    {
        public ResourcePropertiesModel ResourceProperties { get; set; }

        public class ResourcePropertiesModel
        {
            public string Region { get; set; }
        }
    }
}