Introduction:

Serverless architecture has gained immense popularity in recent years due to its scalability, cost-efficiency, and ease of deployment. AWS Lambda, a serverless computing service offered by Amazon Web Services (AWS), allows you to run code in the cloud without the need to provision or manage servers. In this article, we will explore how to build serverless applications using AWS Lambda with C# as the programming language.

Prerequisites:

• An AWS account
• AWS CLI installed on your local machine
• Visual Studio installed on your local machine
• AWS Toolkit for Visual Studio extension installed in Visual Studio

Step 1: Set up AWS Lambda

1. Create an AWS Lambda function using the AWS Management Console or AWS CLI. Choose "Author from scratch" and configure the basic settings such as the function name, runtime (choose C#), and permissions.
2. Once the Lambda function is created, note down the ARN (Amazon Resource Name) of the function, as it will be used later.

Step 2: Set up Visual Studio Project

1. Launch Visual Studio and create a new project using the "AWS Lambda Project (.NET Core)" template.
2. Choose the "Empty Function" blueprint and click on the "Finish" button.
3. In the "Configure triggers" dialog, click on the "Skip" button as we will be configuring the trigger manually.

Step 3: Write Lambda Function Code

1. Open the "Function.cs" file in the project, which contains the Lambda function entry point.
2. Modify the "FunctionHandler" method to implement your desired functionality. For example, let's create a simple function that returns a "Hello, Lambda!" message when invoked.

using Amazon.Lambda.Core;

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]
namespace MyLambdaFunction
{
    public class Function
    {
        public string FunctionHandler(ILambdaContext context)
        {
            return "Hello, Lambda!";
        }
    }
}

Step 4: Publish Lambda Function

1. Right-click on the project in Visual Studio and select "Publish to AWS Lambda" from the context menu.
2. Choose "Create a new Lambda function" and click on the "Next" button.
3. Select the region where you want to deploy the Lambda function and click on the "Create Function" button.
4. In the "Configure Function" dialog, provide a unique function name, choose "Choose an existing role" for the "Execution role" option, and select the appropriate role that allows the Lambda function to execute AWS services. Click on the "Create function" button.
5. In the "Publish" dialog, click on the "Publish" button to deploy the Lambda function code to AWS Lambda.

Step 5: Test Lambda Function

1. Once the Lambda function is published, you can test it using the AWS Management Console or AWS CLI.
2. In the Lambda function configuration page, click on the "Test" button.
3. Create a new test event or choose an existing test event, and click on the "Test" button.
4. You should see the output of the Lambda function in the "Execution result" section, which should be "Hello, Lambda!" in this case.

Congratulations! You have successfully built and deployed a serverless application using AWS Lambda with C#. Now, let's see how you can configure triggers for your Lambda function to invoke it automatically in response to events.

Step 6: Configure Triggers

AWS Lambda supports various event sources that can trigger your Lambda function, such as API Gateway, S3 bucket, SNS topic, and many more. Let's see how you can configure a trigger for your Lambda function to be invoked automatically when an S3 bucket is updated.

1. In the Lambda function configuration page, click on the "Add trigger" button.
2. Choose "S3" as the trigger type.
3. Select the S3 bucket that you want to monitor for updates.
4. Choose the event type for which you want to trigger the Lambda function, such as "All object create events" or "All object delete events".
5. Click on the "Add" button to configure the trigger.
6. You can also configure additional settings for the trigger, such as prefix/suffix filters, batch size, and event source mapping.
7. Click on the "Save" button to save the trigger configuration.

Now, whenever an object is created or deleted in the specified S3 bucket, the Lambda function will be automatically invoked with the event data as input.

using System;
using Amazon.Lambda.Core;
using Amazon.S3;
using Amazon.S3.Util;

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))]
namespace MyLambdaFunction
{
    public class Function
    {
        private readonly IAmazonS3 _s3Client;

        public Function()
        {
            _s3Client = new AmazonS3Client();
        }

        public async void FunctionHandler(S3Event evnt, ILambdaContext context)
        {
            foreach (var record in evnt.Records)
            {
                var bucketName = record.S3.Bucket.Name;
                var objectKey = record.S3.Object.Key;
                var eventType = record.EventName;

                // Perform your desired functionality here
                Console.WriteLine($"Bucket: {bucketName}, Object: {objectKey}, Event: {eventType}");
            }
        }
    }
}

In this example, we are using the Amazon.S3 NuGet package to interact with S3 and handle S3 events in the Lambda function. The FunctionHandler method is configured to accept an S3Event input parameter, which contains the event data of the S3 event that triggered the Lambda function. You can access the bucket name, object key, and event type from the event data and implement your desired functionality accordingly.

Output:

The Lambda function will print the bucket name, object key, and event type in the CloudWatch Logs or in the Visual Studio output window when you test the function or when it is triggered by an S3 event.

Conclusion:

In this article, we learned how to build a serverless application with AWS Lambda using C#. We covered the steps to set up AWS Lambda, create a Lambda function using Visual Studio, write Lambda function code, publish the Lambda function, test the Lambda function, and configure triggers for the Lambda function. We also provided sample code and output to help you understand the concept better. With AWS Lambda and C#, you can easily build scalable and cost-effective serverless applications in the AWS cloud. Happy coding!