C#  

Writing Serverless AWS Lambda in C#

Introduction

Serverless computing is transforming how we design, deploy, and scale applications. With AWS Lambda, developers can run C# code without managing servers or infrastructure, paying only for the compute time they consume. This article explores how to write, deploy, and optimize AWS Lambda functions using C#, covering everything from project setup to advanced patterns.

What is Writing Serverless AWS Lambda in C#?

In this article, I explain how to build a serverless application using AWS Lambda with C#. Lambda lets you run code without provisioning or managing servers, and C# (using .NET Core or .NET 6/7) is fully supported as a Lambda runtime.

Key Concepts

  • AWS Lambda runs small units of code in response to events (HTTP requests, S3 events, DynamoDB streams, etc.).
  • Lambda functions are stateless; they scale automatically.
  • You deploy C# Lambdas as compiled .NET assemblies packaged with a LambdaEntryPoint.

Prerequisites

  • AWS account
  • AWS CLI configured
  • .NET SDK (latest)
  • Amazon.Lambda.Tools (install with dotnet tool install -g Amazon.Lambda.Tools)

Step 1. Create a Lambda Project.

Run the following command.

dotnet new lambda.EmptyFunction -n MyLambdaFunction

This generates a basic Lambda project with a Function.cs file and a LambdaEntryPoint.

Step 2. Write the Lambda Function.

Here’s a simple C# Lambda function that handles an HTTP API Gateway event.

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

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

public class Function
{
    public APIGatewayProxyResponse FunctionHandler(APIGatewayProxyRequest request, ILambdaContext context)
    {
        context.Logger.LogInformation($"Received request: {request.HttpMethod} {request.Path}");

        return new APIGatewayProxyResponse
        {
            StatusCode = 200,
            Body = "Hello from C# Lambda!",
            Headers = new Dictionary<string, string> { { "Content-Type", "text/plain" } }
        };
    }
}

Step 3. Deploy the Lambda.

Build and deploy.

dotnet lambda deploy-function MyLambdaFunction

This will package the app and deploy it to AWS Lambda.

Step 4. Configure Trigger (API Gateway)

  • In the AWS Console, set the Lambda trigger to API Gateway.
  • Configure an HTTP endpoint.
  • Invoke the endpoint: you should see the response "Hello from C# Lambda!"

Advanced Topics

  • Dependency Injection: Use the LambdaStartup class for registering services.
  • Environment Variables: Read from Environment.GetEnvironmentVariable().
  • Cold Start Optimization: Keep initialization outside the handler method.
  • Monitoring: Use AWS CloudWatch Logs and X-Ray for tracing.

Example with Dependency Injection

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

public class LambdaStartup : ILambdaStartup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddLogging();
        services.AddSingleton<IMyService, MyService>();
    }
}

public class Function
{
    private readonly IMyService _service;
    private readonly ILogger<Function> _logger;

    public Function(IMyService service, ILogger<Function> logger)
    {
        _service = service;
        _logger = logger;
    }

    public string FunctionHandler(string input, ILambdaContext context)
    {
        _logger.LogInformation("Handling Lambda invocation");
        return _service.Process(input);
    }
}

Final Notes

Writing serverless AWS Lambda functions in C# gives you the power of .NET in a scalable, cost-effective serverless model. You can integrate with nearly every AWS service, and with the right patterns (DI, logging, tracing), you can build production-grade workloads.

If you want, I can provide.

  • A full sample project with unit tests
  • Advanced patterns like layered deployment and canary releases
  • CloudFormation or CDK templates for automated infrastructure setup

Let me know!

Conclusion

By combining C# with AWS Lambda, you can harness the performance and flexibility of .NET in a modern, serverless architecture. Whether you're building small microservices, backend APIs, or event-driven pipelines, C# on Lambda enables rapid delivery, auto-scaling, and cost efficiency. With careful use of best practices like dependency injection, environment configurations, and monitoring, we can create robust, production-ready serverless applications that fully leverage the AWS ecosystem.

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