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Renato Golia edited this page Apr 17, 2018 · 2 revisions

Here is a tutorial to quickly create an AWS Lambda function using the AWS sdk and a local runner based on the EMG.Lambda.LocalRunner package.

This tutorial assumes that

  • You are confident into using the dotnet console tooling (in this tutorial, PowerShell will be used but no special commandlet will be used)
  • You have some kind of text editor that you can invoke from console (in the tutorial, Visual Studio Code will be used by using the command code)
  • You have some tool to launch HTTP requests, by console or with GUI.

Amazon Lambda Templates

If you haven't done it before, you need to install the templates contained in the Amazon.Lambda.Templates You can do it by simply executing the following command in your favourite shell

> dotnet new -i "Amazon.Lambda.Templates::*"

Create your directory folder

Create a directory for your test project and navigate into it

> md MyTest
> cd MyTest

Create your test Lambda

Let's create a Lambda function to use as target for our runner. In the command prompt of your choice, use dotnet new to create a project containing a simple Lambda project. We will call it MyTestLambda.

> dotnet new lambda.EmptyFunction -n MyTestLambda

The template provided by Amazon will create the following directory structure

MyTestLambda
  - src
    - MyTestLambda
      - aws-lambda-tools-defaults.json
      - Function.cs
      - MyTestLambda.csproj
      - README.md
  - test
    - MyTestLambda.Tests
      - FunctionTest.cs
      - MyTestLambda.Tests.csproj

Creating the local runner

Once we have created the Lambda function, it's time to create the console application that will contain the local runner.

Create the console application

The first step is to create the console application. While staying in the MyTest directory, execute the command

> dotnet new console -n MyLambdaRunner

Ths will create a new directory called MyLambdaRunner within the MyTest one.

Add this package

Let's add the EMG.Lambda.LocalRunner package.

> dotnet add .\MyLambdaRunner\MyLambdaRunner.csproj package EMG.Lambda.LocalRunner
...
info : PackageReference for package 'EMG.Lambda.LocalRunner' version '1.0.0' added to file 'C:\Development\Tests\MyTest\MyLambdaRunner\MyLambdaRunner.csproj'.

Add a reference to the Lambda functon

Now we need to add a reference to the project containing the Lambda function

> dotnet add .\MyLambdaRunner\MyLambdaRunner.csproj reference .\MyTestLambda\src\MyTestLambda\MyTestLambda.csproj
Reference `..\MyTestLambda\src\MyTestLambda\MyTestLambda.csproj` added to the project.

Modify the console application to host the Lambda function

Enter the MyLambdaRunner directory and open the Program.cs file with your text editor of choice.

> cd .\MyLambdaRunner\
> code .\Program.cs

At the beginning of the file, add a using statement to import the namespace of the Lambda function

using MyTestLambda;

Then add a using statement to impor the EMG.Lambda.LocalRunner namespace

using EMG.Lambda.LocalRunner;

In the body of the Main method, replace

Console.WriteLine("Hello World!");

with the following snippet

LambdaRunner.Create()
            .Receives<string>()
            .Returns<string>()
            .UsesFunction<Function>((function, input, context) => function.FunctionHandler(input, context))
            .Build()
            .RunAsync()
            .Wait();

Save everything and leave the editor.

Build and execute the runner

We're now ready to run our application. In the console, let's build and run the console application. Since we have a project reference to the project containing the function, the compiler will also compile it.

> dotnet run
Hosting environment: Production
Content root path: C:\MyTest\MyLambdaRunner\bin\Debug\netcoreapp2.0\
Now listening on: http://127.0.0.1:5000
Application started. Press Ctrl+C to shut down.

The Lambda function is now being hosted on the port 5000. Any HTTP request on that port will be routed to the handler.

Send HTTP requests to execute the Lambda function

Now that our Lambda is being hosted, it's time for us to test it.

If you are using a tool like Postman, Fiddler or similar GUI tools for creating HTTP requests, simply use this raw request

POST  HTTP/1.1
Host: localhost:5000

"hello world"

If you prefer curl in a Linux/MacOSX bash console,

$ curl -X POST http://localhost:5000 -d '"hello world"'
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