ASP.NET Core Web API Serverless Application

This project shows how to run an ASP.NET Core Web API project as an AWS Lambda exposed through Amazon API Gateway. The NuGet package Amazon.Lambda.AspNetCoreServer contains a Lambda function that is used to translate requests from API Gateway into the ASP.NET Core framework and then the responses from ASP.NET Core back to API Gateway.

For more information about how the Amazon.Lambda.AspNetCoreServer package works and how to extend its behavior view its README file in GitHub.

.NET 6 configuration

*.csproj

<TargetFramework>net6.0</TargetFramework>

aws-lambda-tools-defaults.json

"framework": "net6.0",
"function-runtime": "dotnet6",
"function-architecture": "arm64",

Dockerfile

FROM public.ecr.aws/lambda/dotnet:6

AWS SAM Lambda Output

AWS SAM WebAPI (.NET 6.0.10, amzn.2-arm64, Arm64, Arm64) on AWS Lambda with SAM

processor	: 0
BogoMIPS	: 243.75
Features	: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs
CPU implementer	: 0x41
CPU architecture: 8
CPU variant	: 0x3
CPU part	: 0xd0c
CPU revision	: 1

processor	: 1
BogoMIPS	: 243.75
Features	: fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs
CPU implementer	: 0x41
CPU architecture: 8
CPU variant	: 0x3
CPU part	: 0xd0c
CPU revision	: 1

Configuring for API Gateway HTTP API

API Gateway supports the original REST API and the new HTTP API. In addition HTTP API supports 2 different payload formats. When using the 2.0 format the base class of LambdaEntryPoint must be Amazon.Lambda.AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction. For the 1.0 payload format the base class is the same as REST API which is Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction. Note: when using the AWS::Serverless::Function CloudFormation resource with an event type of HttpApi the default payload format is 2.0 so the base class of LambdaEntryPoint must be Amazon.Lambda.AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction.

Configuring for Application Load Balancer

To configure this project to handle requests from an Application Load Balancer instead of API Gateway change the base class of LambdaEntryPoint from Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction to Amazon.Lambda.AspNetCoreServer.ApplicationLoadBalancerFunction.

Project Files

serverless.template - an AWS CloudFormation Serverless Application Model template file for declaring your Serverless functions and other AWS resources
aws-lambda-tools-defaults.json - default argument settings for use with Visual Studio and command line deployment tools for AWS
LambdaEntryPoint.cs - class that derives from Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction. The code in this file bootstraps the ASP.NET Core hosting framework. The Lambda function is defined in the base class. Change the base class to Amazon.Lambda.AspNetCoreServer.ApplicationLoadBalancerFunction when using an Application Load Balancer.
LocalEntryPoint.cs - for local development this contains the executable Main function which bootstraps the ASP.NET Core hosting framework with Kestrel, as for typical ASP.NET Core applications.
Startup.cs - usual ASP.NET Core Startup class used to configure the services ASP.NET Core will use.
web.config - used for local development.
Controllers\ValuesController - example Web API controller

You may also have a test project depending on the options selected.

Packaging as a Docker image.

This project is configured to package the Lambda function as a Docker image. The default configuration for the project and the Dockerfile is to build the .NET project on the host machine and then execute the docker build command which copies the .NET build artifacts from the host machine into the Docker image.

The --docker-host-build-output-dir switch, which is set in the aws-lambda-tools-defaults.json, triggers the AWS .NET Lambda tooling to build the .NET project into the directory indicated by --docker-host-build-output-dir. The Dockerfile has a COPY command which copies the value from the directory pointed to by --docker-host-build-output-dir to the /var/task directory inside of the image.

Alternatively the Docker file could be written to use multi-stage builds and have the .NET project built inside the container. Below is an example of building the .NET project inside the image.

FROM public.ecr.aws/lambda/dotnet:7 AS base

FROM mcr.microsoft.com/dotnet/sdk:7.0-bullseye-slim as build
WORKDIR /src
COPY ["serverless_image_AspNetCoreWebAPI.csproj", "serverless_image_AspNetCoreWebAPI/"]
RUN dotnet restore "serverless_image_AspNetCoreWebAPI/serverless_image_AspNetCoreWebAPI.csproj"

WORKDIR "/src/serverless_image_AspNetCoreWebAPI"
COPY . .
RUN dotnet build "serverless_image_AspNetCoreWebAPI.csproj" --configuration Release --output /app/build

FROM build AS publish
RUN dotnet publish "serverless_image_AspNetCoreWebAPI.csproj" \
            --configuration Release \ 
            --runtime linux-x64 \
            --self-contained false \ 
            --output /app/publish \
            -p:PublishReadyToRun=true  

FROM base AS final
WORKDIR /var/task
COPY --from=publish /app/publish .

Here are some steps to follow from Visual Studio:

To deploy your Serverless application, right click the project in Solution Explorer and select Publish to AWS Lambda.

To view your deployed application open the Stack View window by double-clicking the stack name shown beneath the AWS CloudFormation node in the AWS Explorer tree. The Stack View also displays the root URL to your published application.

Here are some steps to follow to get started from the command line:

Once you have edited your template and code you can deploy your application using the Amazon.Lambda.Tools Global Tool from the command line.

Install Amazon.Lambda.Tools Global Tools if not already installed.

    dotnet tool install -g Amazon.Lambda.Tools

If already installed check if new version is available.

    dotnet tool update -g Amazon.Lambda.Tools

Execute unit tests

    cd "serverless_image_AspNetCoreWebAPI/test/serverless_image_AspNetCoreWebAPI.Tests"
    dotnet test

Deploy application

    cd "serverless_image_AspNetCoreWebAPI/src/serverless_image_AspNetCoreWebAPI"
    dotnet lambda deploy-serverless

IvanFarkas / serverless_image_AspNetCoreWebAPI