Running .NET on AWS Lambda: A Complete Beginner’s Guide

Introduction to AWS Lambda and .NET

AWS Lambda is a serverless computing service that runs code in response to events and automatically manages the underlying infrastructure. With support for .NET Core and .NET 6+, Lambda allows C# developers to run backend logic without provisioning or managing servers.

AWS Lambda supports:

• .NET 6 (LTS)
  
  

• .NET 8 (as a container image)
  
  

• Older versions like .NET Core 3.1 are deprecated as of Dec 2023
  
  

Prerequisites

Before deploying your .NET app to Lambda, ensure you have:

.NET SDK (6 or 8)

AWS CLI installed and configured

AWS Toolkit for Visual Studio (optional for IDE integration)

Amazon.Lambda.Tools global tool:


dotnet tool install -g Amazon.Lambda.Tools

Project Setup

1. Create a New Lambda-Compatible Project

You can use AWS-provided templates:

dotnet new lambda.EmptyFunction --name MyLambdaApp

cd MyLambdaApp

This creates a minimal function using:

• Function.cs: contains the handler
  
  

• aws-lambda-tools-defaults.json: configures deployment details
  
  

2. Sample Function Code

public class Function

{

    public string FunctionHandler(string input, ILambdaContext context)

    {

        return $"Hello from Lambda, input was: {input}";

    }

}

Packaging and Deployment

Option 1: Deploy Using Amazon.Lambda.Tools

dotnet lambda deploy-function MyLambdaApp

This command:

• Packages your code
  
  

• Uploads it to AWS
  
  

• Creates or updates the Lambda function
  
  

Option 2: Deploy as a Container (for .NET 8 or custom dependencies)

Create a Dockerfile:


FROM public.ecr.aws/lambda/dotnet:8 AS base

WORKDIR /var/task

COPY . .

CMD ["MyLambdaApp::MyLambdaApp.Function::FunctionHandler"]

Build and push your Docker image to Amazon ECR, then deploy from the Lambda console or CLI.

Event Triggers

You can connect your Lambda to various AWS services:

• API Gateway (for HTTP triggers)
  
  

• S3 (for object events)
  
  

• DynamoDB Streams
  
  

• CloudWatch Events
  
  

Example: Trigger from API Gateway

{

  "httpMethod": "GET",

  "path": "/hello",

  "headers": { ... }

}

Local Testing

You can run your function locally using:

dotnet lambda invoke-function MyLambdaApp --payload "Test input"

Or use AWS Lambda Test Tool (GUI-based testing tool for .NET):

dotnet tool install -g Amazon.Lambda.TestTool-6.0

dotnet lambda test-tool

Monitoring and Logs

Logs are automatically sent to Amazon CloudWatch. You can:

• View logs in AWS Console under CloudWatch > Logs
  
  

• Set up CloudWatch Alarms
  
  

• Use AWS X-Ray for distributed tracing
  
  

Best Practices

• Use async/await for non-blocking operations
  
  

• Keep the package size small to reduce cold start times
  
  

• Handle exceptions gracefully and log context for debugging
  
  

• Use environment variables for configuration
  
  

• Consider using Amazon Lambda Powertools for .NET for observability