Implementing a Serverless API with .NET Core and AWS Lambda

A detailed guide to building and deploying a serverless API using AWS Lambda and .NET Core, with full code examples and configurations.

Introduction

In this post, we will walk through the process of implementing a serverless API using .NET Core and AWS Lambda. This serverless architecture is becoming the go-to choice for modern web applications due to its scalability, ease of management, and cost-effectiveness.

We'll cover how to build a simple API using .NET Core, deploy it to AWS Lambda, connect it with API Gateway, and secure it with authentication. Let’s get started by setting up the environment.

The following diagram illustrates implementing serverless API with .net core and AWS Lambda:

Setting Up the Development Environment

Before you begin coding, you need to install the following tools:

• Visual Studio 2022: The recommended IDE for developing .NET Core applications.
• AWS Account: A free AWS account to access Lambda and API Gateway.
• AWS Toolkit for Visual Studio: The plugin that integrates AWS services into Visual Studio.
• AWS CLI: Command-line tool to interact with AWS services.

Once you have all the tools installed, you’re ready to start developing the Lambda function.

Creating the .NET Core Lambda Function

Let’s create a simple .NET Core Lambda function that will serve as the backbone of our serverless API.

1. Open Visual Studio and create a new AWS Lambda Project.
2. Choose the "AWS Lambda Project (.NET Core)" template and select the "API Gateway" trigger.
3. Name your project "MyServerlessAPI".

Once the project is created, you will see a default Lambda function file. Let’s modify it to handle a simple HTTP request.

using Amazon.Lambda.APIGatewayEvents;
using Amazon.Lambda.Core;
using Newtonsoft.Json;

public class Function
{
    public APIGatewayProxyResponse FunctionHandler(APIGatewayProxyRequest request, ILambdaContext context)
    {
        var response = new APIGatewayProxyResponse
        {
            StatusCode = 200,
            Body = JsonConvert.SerializeObject(new { message = "Hello from AWS Lambda!" }),
            Headers = new Dictionary<string, string>
            {
                { "Content-Type", "application/json" }
            }
        };

        return response;
    }
}
            

This Lambda function takes an API Gateway request and returns a simple JSON response with a message. You can expand this function to handle more complex API routes later on.

Deploying the Lambda Function to AWS

Now that we have our Lambda function ready, let's deploy it to AWS. Follow these steps:

1. Right-click on the project and select "Publish to AWS Lambda".
2. Choose the AWS region where you want to deploy the function.
3. Set up the necessary IAM role for execution permissions.
4. Click "Publish" to deploy the function to AWS Lambda.

Once the function is deployed, AWS will provide a URL that can be used to trigger your Lambda function via HTTP requests.

Creating API Gateway for Lambda

Next, we will set up API Gateway to create a RESTful API for our Lambda function. API Gateway allows us to expose Lambda functions as HTTP endpoints. To do this:

1. Go to the API Gateway console in the AWS Management Console.
2. Create a new REST API and name it "MyServerlessAPI".
3. Create a new resource and method (GET) for the route "/hello".
4. Link this method to your Lambda function.
5. Deploy the API to a new stage called "prod".

API Gateway will generate an endpoint URL like https://.execute-api..amazonaws.com/prod/hello that you can call to trigger your Lambda function.

Testing the API

Now that we have our API set up, let’s test it. You can use any HTTP client (such as Postman or cURL) to send a GET request to your API Gateway endpoint.

curl -X GET https://.execute-api..amazonaws.com/prod/hello
            

The response should look something like this:

{
    "message": "Hello from AWS Lambda!"
}
            

If you see the expected response, congratulations! You’ve successfully implemented your first serverless API with .NET Core and AWS Lambda.

Securing the API

To secure the API, we can use AWS Cognito for authentication. Here’s how you can set up authentication for your API:

1. Create a Cognito User Pool in the AWS Management Console.
2. Set up an OAuth2 authorization flow.
3. Integrate Cognito with API Gateway to require tokens for accessing the API.

Once you’ve completed these steps, only authenticated users will be able to access the API.

Conclusion

In this tutorial, we’ve built a simple serverless API using .NET Core and AWS Lambda. We covered the basics of creating and deploying Lambda functions, integrating them with API Gateway, and securing the API with AWS Cognito. By using serverless architecture, you can easily scale your APIs and only pay for the compute time that your functions actually use, making it a cost-effective solution for modern applications.

Keep exploring AWS Lambda and other serverless services to build powerful, scalable, and cost-efficient applications!

© 2025 Sandeep Mhaske. All rights reserved.

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