.NET functions with native AOT compilation

To initialize and deploy a native AOT compiled Lambda function

1. Initialize a new project using the native AOT template and then navigate into the directory containing the created .cs and .csproj files. In this example, we name our function NativeAotSample.

   dotnet new lambda.NativeAOT -n NativeAotSample
   cd ./NativeAotSample/src/NativeAotSample

   The Function.cs file created by the native AOT template contains the following function code.

   using Amazon.Lambda.Core;
   using Amazon.Lambda.RuntimeSupport;
   using Amazon.Lambda.Serialization.SystemTextJson;
   using System.Text.Json.Serialization;
   
   namespace NativeAotSample;
   
   public class Function
   {
       /// <summary>
       /// The main entry point for the Lambda function. The main function is called once during the Lambda init phase. It
       /// initializes the .NET Lambda runtime client passing in the function handler to invoke for each Lambda event and
       /// the JSON serializer to use for converting Lambda JSON format to the .NET types.
       /// </summary>
       private static async Task Main()
       {
           Func<string, ILambdaContext, string> handler = FunctionHandler;
           await LambdaBootstrapBuilder.Create(handler, new SourceGeneratorLambdaJsonSerializer<LambdaFunctionJsonSerializerContext>())
               .Build()
               .RunAsync();
       }
   
       /// <summary>
       /// A simple function that takes a string and does a ToUpper.
       ///
       /// To use this handler to respond to an AWS event, reference the appropriate package from
       /// https://github.com/aws/aws-lambda-dotnet#events
       /// and change the string input parameter to the desired event type. When the event type
       /// is changed, the handler type registered in the main method needs to be updated and the LambdaFunctionJsonSerializerContext
       /// defined below will need the JsonSerializable updated. If the return type and event type are different then the
       /// LambdaFunctionJsonSerializerContext must have two JsonSerializable attributes, one for each type.
       ///
       // When using Native AOT extra testing with the deployed Lambda functions is required to ensure
       // the libraries used in the Lambda function work correctly with Native AOT. If a runtime
       // error occurs about missing types or methods the most likely solution will be to remove references to trim-unsafe
       // code or configure trimming options. This sample defaults to partial TrimMode because currently the AWS
       // SDK for .NET does not support trimming. This will result in a larger executable size, and still does not
       // guarantee runtime trimming errors won't be hit.
       /// </summary>
       /// <param name="input"></param>
       /// <param name="context"></param>
       /// <returns></returns>
       public static string FunctionHandler(string input, ILambdaContext context)
       {
           return input.ToUpper();
       }
   }
   
   /// <summary>
   /// This class is used to register the input event and return type for the FunctionHandler method with the System.Text.Json source generator.
   /// There must be a JsonSerializable attribute for each type used as the input and return type or a runtime error will occur
   /// from the JSON serializer unable to find the serialization information for unknown types.
   /// </summary>
   [JsonSerializable(typeof(string))]
   public partial class LambdaFunctionJsonSerializerContext : JsonSerializerContext
   {
       // By using this partial class derived from JsonSerializerContext, we can generate reflection free JSON Serializer code at compile time
       // which can deserialize our class and properties. However, we must attribute this class to tell it what types to generate serialization code for.
       // See https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-source-generation

   Native AOT compiles your application into a single, native binary. The entrypoint of that binary is the static Main method. Within static Main, the Lambda runtime is bootstrapped and the FunctionHandler method set up. As part of the runtime bootstrap, a source generated serializer is configured using new SourceGeneratorLambdaJsonSerializer<LambdaFunctionJsonSerializerContext>()

2. To deploy your application to Lambda, ensure that Docker is running in your local environment and run the following command.

   dotnet lambda deploy-function

   Behind the scenes, the .NET global CLI downloads an AL2023 Docker image and compiles your application code inside a running container. The compiled binary is output back to your local filesystem before being deployed to Lambda.

3. Test your function by running the following command. Replace <FUNCTION_NAME> with the name you chose for your function in the deployment wizard.

   dotnet lambda invoke-function <FUNCTION_NAME> --payload "hello world"

   The response from the CLI includes performance details for the cold start (initialization duration) and total run time for your function invocation.

4. To delete the Amazon resources you created by following the preceding steps, run the following command. Replace <FUNCTION_NAME> with the name you chose for your function in the deployment wizard. By deleting Amazon resources that you're no longer using, you prevent unnecessary charges being billed to your Amazon Web Services account.

   dotnet lambda delete-function <FUNCTION_NAME>