# AWS Lambda Custom Runtime Function Project

This starter project consists of:
* Function.cs - contains a class with a Main method that starts the bootstrap, and a single function handler method
* aws-lambda-tools-defaults.json - default argument settings for use with Visual Studio and command line deployment tools for AWS

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

The generated Main method is the entry point for the function's process.  The main method wraps the function handler in a wrapper that the bootstrap can work with.  Then it instantiates the bootstrap and sets it up to call the function handler each time the AWS Lambda function is invoked.  After the set up the bootstrap is started.

The generated function handler is a simple method accepting a string argument that returns the uppercase equivalent of the input string. Replace the body of this method, and parameters, to suit your needs. 

## Here are some steps to follow from Visual Studio:

(Deploying and invoking custom runtime functions is not yet available in Visual Studio)

## 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](https://github.com/aws/aws-extensions-for-dotnet-cli#aws-lambda-amazonlambdatools) from the command line.  Version 3.1.4
or later is required to deploy this project.

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 "BlueprintBaseName.1/test/BlueprintBaseName.1.Tests"
    dotnet test
```

Deploy function to AWS Lambda
```
    cd "BlueprintBaseName.1/src/BlueprintBaseName.1"
    dotnet lambda deploy-function
```

## Arm64

If you want to run your Lambda on an Arm64 processor, all you need is to do is add `"function-architecture": "arm64"` to the `aws-lambda-tools-defaults.json` file. Then deploy as described above.

## Improve Cold Start

.NET Core 3.1 and newer has a feature called ReadyToRun. When you compile your .NET Core application you can enable ReadyToRun 
to prejit the .NET assemblies. This saves the .NET Core runtime from doing a lot of work during startup converting the 
assemblies to a native format. ReadyToRun must be used on the same platform as the platform that will run the .NET application. In Lambda's case
that means you have to build the Lambda package bundle in a Linux environment. To enable ReadyToRun edit the aws-lambda-tools-defaults.json
file to add /p:PublishReadyToRun=true to the msbuild-parameters parameter.


## Using AWS .NET Mock Lambda Test Tool

The AWS .NET Mock Lambda Test Tool can be used with .NET Lambda custom runtimes. When the test tool is used for custom runtime the project
is executed similar to a Lambda managed runtime and the main method is not called. The test tool uses the `function-handler` field in
the `aws-lambda-tools-defaults.json` file to figure out what code to call when executing a function in it.

To configure the test tool for custom runtimes follow these steps:

* Ensure the `function-handler` is set in the `aws-lambda-tools-defaults.json` for the method to call.
* There is a JSON serializer registered for test tool to using the `LambdaSerializer` assembly attribute.
  * `[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]`
* Ensure the test tool is installed from NuGet. Below is an example for installing the .NET 5.0 version.
  * `dotnet tool install -g Amazon.Lambda.TestTool-5.0` or to update `dotnet tool update -g Amazon.Lambda.TestTool-5.0`
* For Visual Studio edit or add the `Properties\launchSettings.json` to register the test tool as a debug target.
```json
{
  "profiles": {
    "Mock Lambda Test Tool": {
      "commandName": "Executable",
      "commandLineArgs": "--port 5050",
      "workingDirectory": ".\\bin\\$(Configuration)\\net5.0",
      "executablePath": "%USERPROFILE%\\.dotnet\\tools\\dotnet-lambda-test-tool-5.0.exe"
    }
  }
}
```