A template for AWS Lambda functions written in C# with .NET Core 1.0
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README.md

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Project description

Write complex AWS Lambda functions in C#, faster.

This project gives you a strong template that helps you write Lambda functions using C# and .NET Core without giving up on SOLID programming principles.

Overview

This project is designed so that you can create a Lambda function like you create an ASP.NET Core web application. The body of your function becomes your Startup class where the setup and the initialization happens. The real logic of your function is nicely contained into an handler that acts as entry point.

This is what a minimal Lambda function will look like

public class Function : EventFunction<string>
{
    protected override void Configure(IConfigurationBuilder builder) 
    {

    }

    protected override void ConfigureLogging(ILoggerFactory loggerFactory, IExecutionEnvironment executionEnvironment) 
    {

    }

    protected override void ConfigureServices(IServiceCollection services)
    {
        RegisterHandler<EventHandler>(services);
    }
}

The only method required is ConfigureServices that you use to register your handler. You can use ConfigureLogging to add log providers to the provided LoggerFactory. Configure allows you to customize where your settings are taken from. Very much like ASP.NET Core web applications, you can use environment variables, configuration files and in-memory collections.

Type of functions and handlers

AWS Lambda supports two types of invocation, RequestResponse and Event. This distinction is mirrored by offering two distinct base classes.

RequestResponse functions

A RequestResponse function represents a function that produces a return value that will be returned to the caller of the function.

To create a RequestResponse function, simply change your class so that it inherits from RequestResponseFunction<TInput, TOutput> where TInput is a class representing the incoming data and TOutput represents the value your function will produce. Unless specific use cases, TOutput should always be your type, never Task<TOutput>.

A RequestResponse function requires an handler that implements IRequestResponseHandler<TInput, TOutput> to be registered in ConfigureServices.

This is the signature of IRequestResponseHandler<TInput, TOutput>

public interface IRequestResponseHandler<TInput, TOutput>
{
    Task<TOutput> HandleAsync(TInput input, ILambdaContext context);
}

Here you can find a sample that shows a RequestResponse function that returns the input string as upper case.

Event functions

An Event function represents a function that is not expected to produce any value.

To create an Event function, simply change your class so that it inherits from EventFunction<TInput> where TInputis a class representing the incoming data.

An Event function requires an handler that implements IEventHandler<TInput> to be registered in ConfigureServices.

This is the signature of IEventHandler<TInput>

public interface IEventHandler<TInput>
{
    Task HandleAsync(TInput input, ILambdaContext context);
}

Here you can find a sample that shows an Event function that accepts an input string and logs it into CloudWatch logs.

Creating a new function

The best way to create a new AWS Lambda that uses this structure is to use the dotnet new template provided via NuGet.

  1. Ensure you have the .NET Core SDK 1.0.0+ installed.
  2. Open your console prompt of choice and type dotnet new -i "Kralizek.Lambda.Templates::*". This will install the latest version of the templates. Depending on your previous usage of dotnet new, it might take some time.
  3. List all available templates by typing dotnet new -all. You will see 4 new entries, all starting with Lambda.
  4. Create a new project using the template of your choice by typing dotnet new {short name of the template} -n NameOfYourProject. E.g. dotnet new lambda-template-event-empty -n Sample
  5. Start hacking!

Here is a list of all the available templates

Name Short name Description
Lambda Empty Event Function lambda-template-event-empty Creates an Event function with no extra setup
Lambda Empty RequestResponse Function lambda-template-requestresponse-empty Creates a RequestResponse function with no extra setup
Lambda Boilerplate Event Function lambda-template-event-boilerplate Creates an Event function with some boilerplate added
Lambda Boilerplate RequestResponse Function lambda-template-requestresponse-boilerplate Creates a RequestResponse function with some boilerplate added

All the templates support the following parameters

  • --name|-n Name of the project. It is also used as name of the function
  • --role Name of the IAM role the function will use when being executed
  • --region Name of the AWS region where the function will be installed
  • --profile Name of the profile whose credentials will be used when interacting with AWS.

Empty templates

The empty templates are created with just the minimum required dependencies.

These include:

  • Amazon.Lambda.Core
  • Amazon.Lambda.Serialization.Json
  • Kralizek.Lambda.Template
  • Amazon.Lambda.Tools

Boilerplate templates

The boilerplate templates are an enriched version of the empty templates. They contain some extra setup already wired up for you.

  • Logs are automatically pushed to CloudWatch.
  • Settings are loaded from environment variables and a appsettings.json file attached to the project.

Besides the basic dependencies of the empty templates, the boilerplate templates have some extra dependencies.

The extra dependencies are:

  • Amazon.Lambda.Serialization.Json is used to push logs into AWS CloudWatch
  • Kralizek.Extensions.Logging contains several helper methods for better logging
  • Microsoft.Extensions.Configuration.EnvironmentVariables used to load configuration values from environment variables
  • Microsoft.Extensions.Configuration.Json used to load configuration values from json files

Tools

Since the templates are based off the original ones provided by Amazon, you can use dotnet lambda-commands to package/create/deploy/execute your function.