Deploy ASP.NET applications

As well as hosting event-driven functions, you can also use .NET with Lambda to host lightweight ASP.NET applications. You can build and deploy ASP.NET applications using the Amazon.Lambda.AspNetCoreServer NuGet package. In this section, you learn how to deploy an ASP.NET web API to Lambda using the .NET Lambda CLI tooling.

Prerequisites

Deploying an ASP.NET Web API to Lambda

To deploy a web API using ASP.NET, you can use the .NET Lambda templates to create a new web API project. Use the following command to initialize a new ASP.NET web API project. In the example command, we name the project AspNetOnLambda.

dotnet new serverless.AspNetCoreWebAPI -n AspNetOnLambda

This command creates the following files and directories in your project directory.

.
└── AspNetOnLambda
    ├── src
    │   └── AspNetOnLambda
    │       ├── AspNetOnLambda.csproj
    │       ├── Controllers
    │       │   └── ValuesController.cs
    │       ├── LambdaEntryPoint.cs
    │       ├── LocalEntryPoint.cs
    │       ├── Readme.md
    │       ├── Startup.cs
    │       ├── appsettings.Development.json
    │       ├── appsettings.json
    │       ├── aws-lambda-tools-defaults.json
    │       └── serverless.template
    └── test
        └── AspNetOnLambda.Tests
            ├── AspNetOnLambda.Tests.csproj
            ├── SampleRequests
            │   └── ValuesController-Get.json
            ├── ValuesControllerTests.cs
            └── appsettings.json

When Lambda invokes your function, the entry point it uses is the LambdaEntryPoint.cs file. The file created by the .NET Lambda template contains the following code.

namespace AspNetOnLambda;

public class LambdaEntryPoint : Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction
{
    protected override void Init(IWebHostBuilder builder)
    {
        builder
            .UseStartup≪Startup≫();
    }

    protected override void Init(IHostBuilder builder)
    {
    }
}

The entry point used by Lambda must inherit from one of the three base classes in the Amazon.Lambda.AspNetCoreServer package. These three base classes are:

The default class used when you create your LambdaEntryPoint.cs file using the provided .NET Lambda template is APIGatewayProxyFunction. The base class you use in your function depends on which API layer sits in front of your Lambda function.

Each of the three base classes contains a public method named FunctionHandlerAsync. The name of this method will form part of the handler string Lambda uses to invoke your function. The FunctionHandlerAsync method transforms the inbound event payload into the correct ASP.NET format and the ASP.NET response back to a Lambda response payload. For the example AspNetOnLambda project shown, the handler string would be as follows.

AspNetOnLambda::AspNetOnLambda.LambdaEntryPoint::FunctionHandlerAsync

To deploy the API to Lambda, run the following commands to navigate into the directory containing your source code file and deploy your function using AWS CloudFormation.

cd AspNetOnLambda/src/AspNetOnLambda
dotnet lambda deploy-serverless

Deploying ASP.NET minimal APIs to Lambda

To deploy an ASP.NET minimal API to Lambda, you can use the .NET Lambda templates to create a new minimal API project. Use the following command to initialize a new minimal API project. In this example, we name the project MinimalApiOnLambda.

dotnet new serverless.AspNetCoreMinimalAPI -n MinimalApiOnLambda

The command creates the following files and directories in your project directory.

└── MinimalApiOnLambda
    └── src
        └── MinimalApiOnLambda
            ├── Controllers
            │   └── CalculatorController.cs
            ├── MinimalApiOnLambda.csproj
            ├── Program.cs
            ├── Readme.md
            ├── appsettings.Development.json
            ├── appsettings.json
            ├── aws-lambda-tools-defaults.json
            └── serverless.template

The Program.cs file contains the following code.

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();

To configure your minimal API to run on Lambda, you may need to edit this code so that requests and responses between Lambda and ASP.NET Core are properly translated. By default, the function is configured for a REST API event source. For an HTTP API or application load balancer, replace (LambdaEventSource.RestApi) with one of the following options:

To deploy your minimal API to Lambda, run the following commands to navigate into the directory containing your source code file and deploy your function using AWS CloudFormation.

cd MinimalApiOnLambda/src/MinimalApiOnLambda
dotnet lambda deploy-serverless