Create a Lambda Function

Now it's time to create your first Lambda function. You can use the dotnet new command to create a new application from a range of available templates. For this example, we will create an empty Lambda function.

dotnet-new

dotnet new lambda.EmptyFunction -n MyFirstLambda

The created folder structure contains the following files and folders:

MyFirstLambda

└── src

├── MyFirstLambda

├── Function.cs

├── MyFirstLambda.csproj

└── test

├── MyFirstLambda.Test

├── FunctionTest.cs

We will come to tests in a later section, let's first focus on the Lambda function code itself in Function.cs. Open up the MyFirstLambda.csproj in the IDE of your choice.

Lambda Functions in .NET

In it's simplest form, a Lambda function is made up of a single public method. This is the method that will be invoked by the Lambda service. It can be called whatever you want, call it banana if you like.

Typically, it's a good idea to standardize on something along the lines of Handler or FunctionHandler.

Function.cs

using Amazon.Lambda.Core;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

namespace MyFirstLambda;

public class Function

{

/// <summary>

/// A simple function that takes a string and does a ToUpper

/// </summary>

/// <param name="input"></param>

/// <param name="context"></param>

/// <returns></returns>

public string FunctionHandler(string input, ILambdaContext context)

{

return input.ToUpper();

}

}

The Function Handler

The handler itself is a simple method call. It be sync or async, that's up to you. The important parts are the method parameters. A Lambda function handler can take up to 2 parameters.

The first is the payload. This is the event payload the Lambda service will pass into your function. In this example, we are passing in a simple string. But as you will see in later examples this can also be a POCO.

The second is the ILambdaContext. This is an optional parameter, delete it if you wish. The ILambdaContext object holds contextual information about this specific invoke. Things like the RequestId, FunctionName and the FunctionVersion.

Function.cs

using Amazon.Lambda.Core;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

namespace MyFirstLambda;

public class Function

{

/// <summary>

/// A simple function that takes a string and does a ToUpper

/// </summary>

/// <param name="input"></param>

/// <param name="context"></param>

/// <returns></returns>

public string FunctionHandler(string input, ILambdaContext context)

{

return input.ToUpper();

}

}

The Lambda Serializer

The .NET runtime for Lambda can automatically de/serialize Lambda requests and responses to objects and back again. Specifying this line at the top of your function tells Lambda how to perform this de/serialization. There is built in support for System.Text.Json and Newtonsoft.Json as well as the ability to provide your own custom serializer.

Function.cs

using Amazon.Lambda.Core;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

namespace MyFirstLambda;

public class Function

{

/// <summary>

/// A simple function that takes a string and does a ToUpper

/// </summary>

/// <param name="input"></param>

/// <param name="context"></param>

/// <returns></returns>

public string FunctionHandler(string input, ILambdaContext context)

{

return input.ToUpper();

}

}

Lambda Functions in .NET

In it's simplest form, a Lambda function is made up of a single public method. This is the method that will be invoked by the Lambda service. It can be called whatever you want, call it banana if you like.

Typically, it's a good idea to standardize on something along the lines of Handler or FunctionHandler.

The Function Handler

The handler itself is a simple method call. It be sync or async, that's up to you. The important parts are the method parameters. A Lambda function handler can take up to 2 parameters.

The first is the payload. This is the event payload the Lambda service will pass into your function. In this example, we are passing in a simple string. But as you will see in later examples this can also be a POCO.

The second is the ILambdaContext. This is an optional parameter, delete it if you wish. The ILambdaContext object holds contextual information about this specific invoke. Things like the RequestId, FunctionName and the FunctionVersion.

The Lambda Serializer

The .NET runtime for Lambda can automatically de/serialize Lambda requests and responses to objects and back again. Specifying this line at the top of your function tells Lambda how to perform this de/serialization. There is built in support for System.Text.Json and Newtonsoft.Json as well as the ability to provide your own custom serializer.

Function.cs

using Amazon.Lambda.Core;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]

namespace MyFirstLambda;

public class Function

{

/// <summary>

/// A simple function that takes a string and does a ToUpper

/// </summary>

/// <param name="input"></param>

/// <param name="context"></param>

/// <returns></returns>

public string FunctionHandler(string input, ILambdaContext context)

{

return input.ToUpper();

}

}

And that is all there is to your first Lambda function. Feeling good? Now let's go and deploy it to your AWS account.