Amazon SQS (Simple Queue Service) provides a robust mechanism for decoupling systems and processing asynchronous workloads. By combining it with AWS Lambda and .NET, you can build scalable, event-driven applications without managing infrastructure. In this post, you'll learn how to write a .NET Lambda function that processes messages from an SQS queue.

Architecture Overview An application pushes messages to an SQS queue.

AWS Lambda automatically polls the queue.

When messages arrive, Lambda invokes your function with a batch.

Your function processes each message. Create a .NET Lambda Project Start by creating a plain .NET project. You don’t need any special templates for this walkthrough. dotnet new console -n SqsLambdaProcessor cd SqsLambdaProcessor Add The Necessary AWS Lambda Packages dotnet add package Amazon.Lambda.Core dotnet add package Amazon.Lambda.SQSEvents dotnet add package Amazon.Lambda.Serialization.SystemTextJson Rename Program.cs to Function.cs, or create a new Function.cs file, and define your handler: using Amazon.Lambda.SQSEvents; using Amazon.Lambda.Core; [assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer))] public class Function { public async Task FunctionHandler(SQSEvent evnt, ILambdaContext context) { foreach (var message in evnt.Records) { await ProcessMessageAsync(message, context); } } private Task ProcessMessageAsync(SQSEvent.SQSMessage message, ILambdaContext context) { context.Logger.LogLine($"Processing message {message.MessageId}: {message.Body}"); // Add your business logic here return Task.CompletedTask; } } Deploy the Lambda To Deploy, You Can Use The AWS CLI, AWS Console, Or The AWS Toolkit For Visual Studio.

Here's How To Deploy Using The AWS CLI With The Lambda .NET Tooling Package the project:



dotnet lambda package --output-package bin/release/sqs-lambda.zip Deploy the function: aws lambda create-function --function-name SqsLambdaProcessor --runtime dotnet6 --handler SqsLambdaProcessor::SqsLambdaProcessor.Function::FunctionHandler --zip-file fileb://bin/release/sqs-lambda.zip --role arn:aws:iam::YOUR_ACCOUNT_ID:role/YOUR_LAMBDA_EXECUTION_ROLE Replace the role ARN with your vigente IAM role that allows Lambda execution and access to SQS. Connect the SQS Queue You can configure the SQS queue as an event source: aws lambda create-event-source-mapping --function-name SqsLambdaProcessor --event-source-arn arn:aws:sqs:us-east-1:123456789012:your-queue-name --batch-size 5 Test Locally You Can Write Unit Tests Using The Amazon.Lambda.TestUtilities Package dotnet add package Amazon.Lambda.TestUtilities Example Test [Fact] public async Task TestHandlerProcessesMessages() { var function = new Function(); var context = new TestLambdaContext(); var sqsEvent = new SQSEvent { Records = new List { new SQSEvent.SQSMessage { Body = "Test Message" } } }; await function.FunctionHandler(sqsEvent, context); } Error Handling and Retries Lambda Automatically Retries Failed Messages.

To Handle Failures

Implement try-catch inside ProcessMessageAsync.

Set up a Dead Letter Queue (DLQ) on your Lambda or SQS.

Use structured logging to track errors.

Best Practices

Make your function idempotent to handle retries safely.

Tune batch size to optimize throughput vs. memory usage.

Keep Lambda’s timeout below the SQS visibility timeout.

Log enough information to troubleshoot failures.

Cleanup To Remove The

Resources aws lambda delete-function --function-name SqsLambdaProcessor aws sqs delete-queue --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/your-queue-name References Amazon SQS

AWS Lambda with SQS

Amazon.Lambda.SQSEvents on NuGet

AWS .NET Lambda Tools GitHub

📌 Processing SQS Messages with .NET Lambda (Jun)
🏢 Renato Gonçalves
📍 Jun