Stateful Serverless ASP.NET Core API

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.

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.tf - an Terrafrom file for declaring your Serverless functions and other AWS resources
• 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.
• Controllers\HomeController - example API controller

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.

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:6 AS base

FROM mcr.microsoft.com/dotnet/sdk:6.0-bullseye-slim as build
WORKDIR /src
COPY ["Api.csproj", "Api/"]
RUN dotnet restore "Api/Api.csproj"

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

FROM build AS publish
RUN dotnet publish "Api.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 .