Building Serverless .NET Core Applications with AWS Lambda

Serverless architectures continue to reshape how developers build scalable, event-driven applications. With the rise of cloud providers offering Function-as-a-Service (FaaS) platforms, AWS Lambda stands out as one of the most popular solutions. Combining AWS Lambda with .NET Core allows developers to write performant, scalable functions in C# that respond to events without managing infrastructure.

What Is AWS Lambda?

AWS Lambda is a serverless compute service that runs your code in response to events and automatically manages the underlying compute resources. This means you don’t worry about provisioning or maintaining servers. Instead, you focus purely on your business logic.

AWS Lambda supports multiple runtimes, including .NET Core (now known as .NET 6/7/8), allowing C# developers to build and deploy serverless functions seamlessly.

Why Use Serverless with .NET Core?

Serverless with .NET Core offers several advantages:

• Event-driven: Easily respond to HTTP requests, database changes, file uploads, messaging queues, and more.
• Automatic scaling: Lambda scales your functions automatically based on demand, with no manual intervention.
• Cost-efficient: You pay only for the compute time your functions consume.
• Fast deployments: Rapidly iterate and deploy individual functions.
• Integration: Deep integration with AWS services like API Gateway, DynamoDB, S3, SNS, and EventBridge.

Building Your First .NET Core Lambda Function

Let’s walk through creating a simple AWS Lambda function in C# that responds to HTTP requests via API Gateway.

Prerequisites

• AWS CLI installed and configured with your credentials.
• .NET 7 SDK installed.
• AWS Toolkit for Visual Studio or VS Code (optional, but helpful).
• An AWS account.

Step 1: Create a New Lambda Project

Run the following command to create a new AWS Lambda HTTP API project:

dotnet new lambda.AspNetCoreWebAPI -n MyServerlessApi
cd MyServerlessApi

This template sets up a minimal ASP.NET Core Web API project ready to deploy as a Lambda function.

Step 2: Implement Your API Endpoint

Open Controllers/FunctionController.cs and add a simple GET endpoint:

[ApiController]
[Route("[controller]")]
public class FunctionController : ControllerBase
{
    [HttpGet]
    public IActionResult Get()
    {
        return Ok(new { message = "Hello from AWS Lambda and .NET Core!" });
    }
}

Step 3: Deploy to AWS Lambda

To deploy the function, first publish your project:

dotnet lambda deploy-serverless

This command will guide you through packaging and deploying your Lambda function and configuring the API Gateway endpoint.

Once deployed, you’ll get an API Gateway URL where you can test your function by opening the URL in a browser or calling it with curl:

curl https://your-api-id.execute-api.region.amazonaws.com/Function

You should see:

{ "message": "Hello from AWS Lambda and .NET Core!" }

Event-Driven Microservices with Lambda

AWS Lambda excels when used for event-driven microservices. Instead of a monolithic app, you can split business logic into small, independently deployable functions that trigger on specific events:

• S3 events: Process images or files when uploaded to S3.
• DynamoDB streams: React to data changes in DynamoDB tables.
• SNS topics: Send notifications or trigger workflows.
• EventBridge: Respond to scheduled events or cross-service signals.

For example, a Lambda function could listen to an S3 bucket upload event and generate thumbnails for images automatically, without spinning up any servers.

Best Practices for Serverless .NET Core on Lambda

• Keep functions small and focused: Each Lambda function should handle a single responsibility.
• Use dependency injection: .NET Core’s built-in DI works well even in Lambda.
• Leverage async/await: For better scalability and non-blocking I/O.
• Monitor and log: Use AWS CloudWatch for logging and setting alarms.
• Optimize cold starts: Keep your deployment packages lean, and consider provisioned concurrency for critical functions.

Conclusion

Using AWS Lambda with .NET Core opens the door to truly scalable, event-driven applications with minimal infrastructure management. Whether you’re building APIs, microservices, or background processing tasks, Lambda’s serverless model lets you focus on writing clean code and delivering business value.

If you’re new to serverless, start small with simple event handlers and grow your architecture organically. For more advanced scenarios, explore integrating Lambda with Step Functions for orchestrations or API Gateway for rich HTTP APIs.