My first C# AWS Lambda Function

July 29, 2021 #aws #lambda #csharp #dotnet

Here it is - my very first AWS Lambda Function coded in C#.

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

using Amazon.Lambda.Core;
using Amazon.Lambda.APIGatewayEvents;

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

namespace MyFirstCsharpLambda
{
    public class Functions
    {
        /// <summary>
        /// Default constructor that Lambda will invoke.
        /// </summary>
        public Functions()
        {
        }


        /// <summary>
        /// A Lambda function to respond to HTTP Get methods from API Gateway
        /// </summary>
        /// <param name="request"></param>
        /// <returns>The API Gateway response.</returns>
        public APIGatewayProxyResponse Get(APIGatewayProxyRequest request, ILambdaContext context)
        {
            context.Logger.LogLine("Get Request\n");

            var response = new APIGatewayProxyResponse
            {
                StatusCode = (int)HttpStatusCode.OK,
                Body = "Hello AWS Serverless",
                Headers = new Dictionary<string, string> { { "Content-Type", "text/plain" } }
            };

            return response;
        }
    }
}

You can probably guess I didn’t write that code, but generated it from a template. There is .NET Core CLI support for creating .NET-based Lambda applications.

$ dotnet tool install -g Amazon.Lambda.Tools
$ dotnet new -i Amazon.Lambda.Templates
$ dotnet new serverless.EmptyServerless --name MyFirstCsharpLambda

Most of my Lambda functions have been JavaScript/Node.js where I am processing the fields on a loosely types event object, so it was nice to see the LambdaSerializer helps create strongly typed APIGatewayProxyRequest and APIGatewayProxyResponse objects to understand the event payload.

public APIGatewayProxyResponse Get(APIGatewayProxyRequest request, ILambdaContext context)

I used to code C# using Visual Studio on Windows Desktop and run under IIS on Windows Server, and now my C# development uses Visual Studio Code on macOS and runs on AWS Lambda on Linux.