Lambda

Links

• Running .NET 8 Lambda Functions on AWS using Custom Runtime & Lambda Internals

Description

Serverless service / Function as a service allowing to run code without having to worry about underlying hardware and OS.
Event driven: the lambda is triggered by an event.
Pay only for what you use: per request and based on the duration of the code execution.

Use cases

• Data transformation (Kinesis Data Stream as input)
• File processing (when uploaded to S3 bucket)
• Website backend microservice
• Scheduled tasks

Bad use cases

• Long running processes (timeout after 15mn)
• Constant workload (no scalability and high cost)
• Large code base (needed to be loaded at startup)
• State management (lambda are stateless)

Anti-patterns

• Monolithic function
  • increase package size
  • hard to enforce least privilege permissions
  • hard to upgrade, maintain and test
• Recursion
  • endless loop
• Orchestration
  • avoid complex workflow logic
  • ties lambda with other systems
  • instead consider AWS Step Functions or EventBridge
• Chaining (synchronously invoke another lambda)
  • instead use EventBridge or QueueService
• Waiting (synchronously call services or databases)
  • instead use asynchronous calls

Runtime

• OS
• Libraries
• Programming language (.NET, Node.js, Python, Go, Ruby, Java)

Environnement variables

DOTNET_STARTUP_HOOKS

ex: path to an assembly to inject logging

Wrapper scripts

Execute the wrapper on top of the runtime and the lambda function.

• run shell commands and binaries

Use AWS_LAMBDA_EXEC_WRAPPER to point to your wrapper script.

Custom runtime

Provide your custom runtime.

• unsupported programming language

Handler (entry point)

Method responsible for processing input events.

[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.SystemTextJson.CamelCaseLambdaJsonSerializer))] namespace MyNamespace; public class Function { public APIGatewayProxyResponse Handle(APIGatewayProxyRequest request, ILambdaContext context) { var id = request.PathParameters["id"]; var function = $"{context.FunctionName} {context.FunctionVersion}"; var cognitoIdentity = context.Identity; context.Logger.LogLine("Message"); return new APIGatewayProxyResponse { StatusCode = (int)HttpStatusCode.OK, Body = JsonSerializer.Serialize(id) }; } public void Handle(SQSEvent sqsEvent, ILambdaContext context) { } }

synchronous execution	result returned to the calling app
asynchronous execution	result sent to the configured destination otherwise lost

.NET 8

scenario	description
Native AOT
Custom Runtime Function	to use .NET 8
Container Image	lambda function package as a container image

Debug locally

On VS, if the extension AWS Toolkit is installed you have the AWS .NET Mock Lambda Test Tool available.
A debug configuration is created for you lambda.

Properties\launchSettings.json

{ "profiles": { "Mock Lambda Test Tool": { "commandName": "Executable", "commandLineArgs": "--port 5050", "executablePath": "<home-directory>\\.dotnet\\tools\\dotnet-lambda-test-tool-6.0.exe", "workingDirectory": ".\\bin\\Debug\\net6.0" } } }

Deployment

Lambda function handler in C#

For class libraries: ASSEMBLY::TYPE::METHOD

Call a lambda from code

var jsonSerializerOptions = new JsonSerializerOptions { PropertyNamingPolicy = JsonNamingPolicy.CamelCase, Converters = { new JsonStringEnumConverter() } }; var amazonLambdaClient = new AmazonLambdaClient(); var request = new InvokeRequest { FunctionName = functionName, Payload = JsonSerializer.Serialize(myObject, jsonSerializerOptions), LogType = LogType.Tail }; var response = await this.amazonLambdaClient.InvokeAsync(request); if(response.HttpStatusCode == System.Net.HttpStatusCode.OK) { var payload = Encoding.ASCII.GetString(response.Payload.ToArray()); // to debug only var result = JsonSerializer.Deserialize<AwsJobResult<LambdaJob>>(response.Payload, jsonSerializerOptions); }