Building Serverless .NET Minimal API (using Controller) with AWS Lambda

2 min readNov 4, 2022

We will create a minimal API using AWS Lambda and .NET 6. It will be a simple API with a single MapGet method and a single controller which is a simple calculator class with four methods.

Creating a new project

We are going to use the serverless.AspNetCoreMinimalAPI template. You can create a new project using the following command:

dotnet new serverless.AspNetCoreMinimalAPI --name MinimalLambda --output MinimalLambda

or using the Rider IDE.

Configuring the project

We need to configure aws-lambda-tools-defaults.json file.

This time we will use function-handler as MinimalLambda. Then we can remove serverless.template file.

Looking at the code

In the Program.cs file, we have a CreateHostBuilder method. This method will create a new IHostBuilder instance.

var builder = WebApplication.CreateBuilder(args);// Add services to the container.
builder.Services.AddControllers();// Add AWS Lambda support. When application is run in Lambda Kestrel is swapped out as the web server with Amazon.Lambda.AspNetCoreServer. This
// package will act as the webserver translating request and responses between the Lambda event source and ASP.NET Core.
builder.Services.AddAWSLambdaHosting(LambdaEventSource.RestApi);var app = builder.Build();
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();app.MapGet("/", () => "Welcome to running ASP.NET Core Minimal API on AWS Lambda");app.Run();

LambdaEventSource.RestApi is the event source that will be used to handle the request. If we change it to LambdaEventSource.HttpApi, we will be able to use the new HTTP API.

builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi);

In the Controllers folder, we have a CalculatorController.cs file. This file contains a Calculator class with four methods. We can use these methods to perform simple calculations.

Deploying the project

Now that we have created the project, we can deploy it to AWS Lambda. Go to the project directory and run the following command:

dotnet lambda deploy-function

With "function-url-enable": true in aws-lambda-tools-defaults.json file, we can get the function URL after deploying the project.

Now we can use the function URL to access the API.

They can be accessed using the following URLs:

https://<function-url>/calculator/add/1/2
https://<function-url>/calculator/subtract/1/2
https://<function-url>/calculator/multiply/1/2
https://<function-url>/calculator/divide/1/2

With Postman, we can send a request to these URLs and get the result.

Congratulations!

You have created a minimal API using AWS Lambda and .NET 6.