In this post, we will understand how can we implement the following things when using AWS Lambda with .NET Core.

• Configuration
• Logging
• Dependency Injection

Overview

When we create an AWS Lambda project in Visual Studio, we just get basic FunctionHandler method inside Function class.

.NET Core features such as Configuration, Logging & Dependency Injection are not enabled by default. We need to write some additional code to enable these features.

Although, Logging is enabled by default, but that uses lambda logger, not .NET Core's default logger.

Implementation - Configuration, Logging & Dependency Injection

We will be implementing following things in this post further.

• Configuration - Configuration support with appsettings.json file & Environment Variables.
• Logging - Logging support with default Console logging.
• Dependency Injection - DI support by adding services in ServiceCollection.

Step 1: Install NuGet packages

We would need below packages to implement Configuration, Logging & Dependency Injection in our Lambda project. Just update csproj file to have ItemGroup section like below, or install these packages manually.

<ItemGroup>
	<!-- Default Lambda packages specific to Lambda  -->
	<PackageReference Include="Amazon.Lambda.Core" Version="2.1.0" />
	<PackageReference Include="Amazon.Lambda.Serialization.SystemTextJson" Version="2.3.0" />
		
	<!-- Packages required for Dependency Injection -->
	<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="6.0.0" />
	<PackageReference Include="AWSSDK.Extensions.NETCore.Setup" Version="3.7.2" />
	<PackageReference Include="AWSSDK.S3" Version="3.7.9.2" />

	<!-- Packages required for Configuration -->
	<PackageReference Include="Microsoft.Extensions.Configuration" Version="6.0.1" />
	<PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="6.0.1" />
	<PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="6.0.0" />
	<PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="6.0.0" />
	<!---->

	<!-- Packages required for Logging -->
	<PackageReference Include="Microsoft.Extensions.Logging" Version="6.0.0" />
	<PackageReference Include="Microsoft.Extensions.Logging.Console" Version="6.0.0" />
</ItemGroup>

Step 2: Create a Startup class file

Create a Startup.cs class file with below content. Code is self explanatory.

public class Startup
{
    public IServiceProvider Setup()
    {
        var configuration = new ConfigurationBuilder() // ConfigurationBuilder() method requires Microsoft.Extensions.Configuration NuGet package
                .SetBasePath(Directory.GetCurrentDirectory())  // SetBasePath() method requires Microsoft.Extensions.Configuration.FileExtensions NuGet package
                .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true) // AddJsonFile() method requires Microsoft.Extensions.Configuration.Json NuGet package
                .AddEnvironmentVariables() // AddEnvironmentVariables() method requires Microsoft.Extensions.Configuration.EnvironmentVariables NuGet package
                .Build();

        var services = new ServiceCollection(); // ServiceCollection require Microsoft.Extensions.DependencyInjection NuGet package

        // Add configuration service
        services.AddSingleton<IConfiguration>(configuration);

        // Add logging service
        services.AddLogging(loggingBuilder =>  // AddLogging() requires Microsoft.Extensions.Logging NuGet package
        {
            loggingBuilder.ClearProviders();
            loggingBuilder.AddConsole(); // AddConsole() requires Microsoft.Extensions.Logging.Console NuGet package
        });


        ConfigureServices(configuration, services);

        IServiceProvider provider = services.BuildServiceProvider();

        return provider;
    }

    private void ConfigureServices(IConfiguration configuration, ServiceCollection services)
    {
        #region AWS SDK setup
        // Get the AWS profile information from configuration providers
        AWSOptions awsOptions = configuration.GetAWSOptions();

        // Configure AWS service clients to use these credentials
        services.AddDefaultAWSOptions(awsOptions);

        // These AWS service clients will be singleton by default
        services.AddAWSService<IAmazonS3>();
        #endregion
           
        services.AddSingleton<IProgramEntryPoint, ProgramEntryPoint>();
    }
}

You may also need to add below namespaces.

using Amazon.Extensions.NETCore.Setup;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

Step 3: Create ProgramEntryPoint class

Create ProgramEntryPoint class with Handler method. Inject all the dependencies inside the constructor of this class. We will invoke Handler method of this class from original FunctionHandler.

3.1. IProgramEntryPoint interface

public interface IProgramEntryPoint
{
    Task<string> Handler(string input);
}

3.2. ProgramEntryPoint class

public class ProgramEntryPoint : IProgramEntryPoint
{
    private readonly ILogger<ProgramEntryPoint> _logger;

    public ProgramEntryPoint(ILogger<ProgramEntryPoint> logger)
    {
        _logger = logger;
    }

    public async Task<string> Handler(string input)
    {
        _logger.LogInformation("Handler invoked");

        return $"Hello {input}";
    }
}

4. Modify Function.cs class

Now replace Function class content with below content.

Here, we are mainly doing 2 things:

1. Inside constructor, we are calling Setup() method of Startup class. This method will setup everything and will return an instance of IServiceProvider.
2. Inside FunctionHandler, we are calling _programEntryPoint.Handler(input) method to do the actual processing.

Also, it is important to understand, Function class is Singleton in AWS Lambda. Multiple invocations of AWS Lambda will not execute Constructor logic multiple times, that will be executed only once in the beginning, and class will remain singleton until Lambda compute is alive.

public class Function
{
    private readonly IProgramEntryPoint _programEntryPoint;

    public Function()
    {
        var startup = new Startup();
        IServiceProvider provider = startup.Setup();

        _programEntryPoint = provider.GetRequiredService<IProgramEntryPoint>();
    }

    public async Task<string> FunctionHandler(string input, ILambdaContext context)
    {
        return await _programEntryPoint.Handler(input);
    }

}

That's all.

Conclusion

In this post, we learned how easily we can setup configuration, logging and dependency injection in AWS Lambda when using with .NET Core. Please let me know your thoughts and feedback in the comment section below.

Thank You ❤️