ASP.NET Core Web API AWS Lambda

I am using the below two tools.

• AWS Lambda for .NET Core
• .NET Core CLI

Blueprint types

Blueprint and template are interchangeable words here.

serverless.AspNetCoreWebAPI

dotnet new serverless.AspNetCoreWebAPI

Removed the S3Controller and related config vars and injector.

This assumes you have .aws\credentials setup in home directory.

Edit aws-lambda-tools-defaults.json update profile and region fields. Otherwise i got Error retrieving configuration for function The operation was canceled when deploying.

Here you can use attributes.

Related videos

• Create a Serverless .NET Core 2.1 Web API with AWS Lambda
• Create & Deploy Serverless Dot Net Core Web API with Lambda Fucntion & API Gateway

Related blog posts

• Creating a Serverless Application with ASP.NET Core, AWS Lambda and AWS API Gateway

So its not just me who removes the extra bits or creates the API Gateway manually.

Blueprint method signature:

[HttpGet("{id}")]
public string Get(int id)

public void, public string or public IActionResult all work.

Modified example

Based on ASP.NET Core 3.1

bitbucket.org/2E0PGS/aws-serverless-aspnet-core-api

cURL example

Request

curl --request POST \
  --url https://redacted.execute-api.eu-west-1.amazonaws.com/default/v1/values \
  --header 'content-type: application/json' \
  --header 'x-api-key: redacted' \
  --data '{
	"data": "testing"
}'

Response

{
    "motd": "Hello from AWS serverless.",
    "data": "testing",
    "environmentMachineName": "169",
    "environmentDirectory": "/var/task",
    "environmentSystemDirectory": "",
    "currentCulture": "English (United States)",
    "currentDateTimeUtc": "2020-09-30T17:19:50.8216401Z",
    "method": "POST"
}

Insomnia example

lambda.EmptyFunction

dotnet new lambda.EmptyFunction

Edit aws-lambda-tools-defaults.json update profile and region fields. Already comes with a function-handler JSON field.

Works but isn’t designed for API Gateway input really. Just basic string input.

Blueprint method signature: public string FunctionHandler(RequestModel requestModel, ILambdaContext context)

Example

public string FunctionHandler(RequestModel requestModel, ILambdaContext context)
{
    return requestModel.lowercase?.ToUpper();
}

serverless.EmptyServerless

dotnet new serverless.EmptyServerless

Edit aws-lambda-tools-defaults.json update profile and region fields.

Blueprint method signature: public APIGatewayProxyResponse Get(APIGatewayProxyRequest request, ILambdaContext context)

I would have to discern the request type based on request.HttpMethod. I am not sure if you can use the ASP attributes here.

Modified example

public APIGatewayProxyResponse Post(APIGatewayProxyRequest request, ILambdaContext context)
{
    context.Logger.LogLine("Post Request\n");

    var response = new APIGatewayProxyResponse
    {
        StatusCode = (int)HttpStatusCode.OK,
        Body = "Hello from AWS Serverless." +
        "\n This is a 2E0PGS test" +
        "\n Request body: " + request.Body + 
        "\n Environment directory: " + Environment.CurrentDirectory + 
        "\n Environment machinename: " + Environment.MachineName + 
        "\n Environment version: " + Environment.Version +
        "\n Datetime: " + DateTime.Now.ToLongDateString() + 
        "\n Culture: " + CultureInfo.CurrentCulture.DisplayName + 
        "\n Method: " + request.HttpMethod,
        Headers = new Dictionary<string, string> { { "Content-Type", "text/plain" } }
    };

    return response;
}

Insomnia example

Deploy types

deploy-function

Deploys just the Lambda function itself. I think this is much simpler and doesn’t require a S3 bucket.

However you need to carefully configure the API Gateway from default to work with an existing Lambda Function with a API Gateway trigger created using the AWS console (web UI) as I describe what will happen otherwise below.

I have to hack the aws-lambda-tools-defaults.json to include a function-handler and a function-runtime based on serverless.template AwsServerlessAspNetCore.Api::AwsServerlessAspNetCore.Api.LambdaEntryPoint::FunctionHandlerAsync

You have to specify runtime. dotnetcore3.1 unless you define it in aws-lambda-tools-defaults.json under property: function-runtime

They probably prefer you using the serverless.template because it adds the method routing into API Gateway automatically. Otherwise you may run into the below.

Default API Gateway routes

Doesn’t work, returns 405 method not allowed.

[HttpPost]
public string Post([FromBody]string value)

The below do work, returns 200. This appears to be a routing issue.

[HttpPost("{id}")]
public string Post([FromBody]string value)

[HttpPost("{anything}")]
public string Post([FromBody]string value)

[HttpPost]
[Route("{anything}")]
public string Post([FromBody]string value)

It will return unsupported media type for POST unless you send with header Content-Type application/json

Using API Gateway proxy+ route

Working routing on this without ASP “route template” if using {proxy+}

    [Route("v1/values")]
    public class ValuesController : ControllerBase
    {
        [HttpPost]
        public string Post([FromBody]string value)

Manually add auth via API key: Set up API keys using the API Gateway console

Repeat after me, I will not forget to deploy my API Gateway: AWS API Gateway: Solving Missing Authentication Tokens

Run: dotnet lambda deploy-function

deploy-serverless

Edit: aws-lambda-tools-defaults.json update profile and region fields.

Edit: serverless.template

Run: dotnet lambda deploy-serverless --region eu-west-1

It uses AWS CloudFormation to create a S3 bucket to store the code and setup a AWS API Gateway with {proxy+} routes.