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.

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

Configuration

Setting	Description
Memory	from 128 MB (default) to 10 GB
vCPU	1'769 MB = 1 vCPU, 10 GB = 6 vCPU, for single-threaded code allocated more than 1'769 MB is useless. Compare ARM and x86.
timeout	from 1s to 15mn, default to 3s
VPC	by default no VPC access configured → Amazon VPC → internet access if VPC access is configured → access to VPC resources → no internet connection use an Hyperplane ENI to add internet connection in addition of a VPC access
Ephemeral storage	/tmp from 512 MB (default) to 10 GB
Execution role	grants permissions to access AWS services
Resource-based policy	define what others are allowed to do to the function
Environment variables	Key-value pair of strings Stored in the configuration for a Lambda function version Accessible within the Lambda code function
Logging	format (text or JSON), level, group

Storage

Directories

Path	Description
/var/task	Lambda package (function files)
/tmp	Temporary storage with write access
/opt	Lambda layer (layer files)

Elastic File System (EFS)

• Persistent
• Serverless, scalable
• Support concurrent access
• Require VPC access

S3

• Persistent
• No VPC required
• Accessed via API

IAM entities

Type	Description
User	individual with unique credentials
Role	entity for temporary access (access to a db)
Policy	permission for access to resources (apply to a user or a role to read from a specific db table)
User group	logical collection of users for easier management

Synchronous execution

Invocation result

Result content	Description
Status code	200 success, 4xx or 5xx error
Executed version
Log result	last 4 KB of the execution log in base64 encoding
Function error	only if an error occured. Code error, timeout, invalid JSON output
Response body	payload

Asynchronous execution

The Lambda is executed and its result (Invocation Record) is sent to a destination.

Destinations

• Simple Notification Service (SNS) topic
• Simple Queue Service (SQS) queue
• Lambda function
• EventBridge event bus

Event Source

• Simple Queue Service (SQS) queue
• DynamoDB stream
• DocumentDB stream
• Kinesis data stream
• Message Queue (MQ)
• Kafka

Lambda has builtin functionalities to poll the event source with batching and filtering functionality.
Event source mapping polls and gathers records before it will initialize a Lambda function and send a batch of events to it for processing.

Error handling

If the invocation errors, then it will try the same invocation again after a minute.
After X fails that exceeds the configured retry attempts (0, 1 or 2), the failed invocation goes to:

• a dead-letter queue
• a failure destination

Optimization

Make the most of warm start

The initialization of the function is run only during the cold start.
During the warm start the environment is thawed and only the function handler is executed. Use function initialization to: (outside of the handler function)

• load external libraries
• open db connection
• load configuration and secrets
• use the ephemeral storage, such as a local cache for files

SnapStart

Only for Java runtime

Lambda initializes the function at publish rather than during cold-start invocation.
If not invoked, snapshots are deleted after 14 days.
Limitations:

• cannot be used with provisioned concurrency
• supports limited runtimes, architecture and ephemeral storage

Ensure to (with post-snapshot hook):

• reestablish network connections
• have preloaded data up to date
• take care of uniqueness (generation of random numbers or GUID), each function starts with a clone of the snapshot

Concurrency

• Lambda function scaling

Concurrency type	Description
Account concurrency	max number of concurrent instances across all functions (AWS → Lambda → Dashboard)
Reserved concurrency	upper limit of a function's concurrency
Burst concurrency	increase quota, default to 1'000 instances every 10 s
Provisioned concurrency	initialize execution env ahead of time. Application Auto Scaling can be used to automatically adjust provisioned concurrency

Setting up your .NET development environment

# install the VS project template dotnet new install Amazon.Lambda.Templates # install the command line tools dotnet tool install -g Amazon.Lambda.Tools

Install the AWS Toolkit for Visual Studio extension.

AWS Lambda application types

AWS Lambda application type	Description
Class library
Executable assembly
AWS Serverless Application	ASP.NET application hosted in the AWS environment. It has a handful of additional dependencies that make it interoperate with AWS runtime.

C# class library

You provide Lambda with information about your function's handler in the form of a handler string: ASSEMBLY::TYPE::METHOD

• ASSEMBLY is the name of the .NET assembly file for your application. If you use the Amazon.Lambda.Tools CLI to build your application and you don't set the assembly name using the AssemblyName property in the .csproj file, then ASSEMBLY is simply the name of your .csproj file.
• TYPE is the full name of the handler type, which consists of the Namespace and the ClassName.
• METHOD is the name of the function handler method in your code.

ex: MyProject::MyNamespace.MyClass::MyFunctionHandler

Function.cs

// 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 MyProject; public class Function { public string FunctionHandler(string input, ILambdaContext context) { return input.ToUpper(); } }

aws-lambda-tools-defaults.json

{ "Information": [ ], "profile": "MyAwsProfile", "region": "eu-central-1", "configuration": "Release", "function-architecture": "x86_64", "function-runtime": "dotnet8", "function-memory-size": 512, "function-timeout": 30, "function-handler": "MyProject::MyProject.Function::FunctionHandler" }

On VS, if the extension AWS Toolkit is installed, you have the AWS .NET Mock Lambda Test Tool available which allows you to debug locally.

Properties/launchSettings.json

{ "profiles": { "Mock Lambda Test Tool": { "commandName": "Executable", "commandLineArgs": "--port 5050", "workingDirectory": ".\\bin\\$(Configuration)\\net8.0", "executablePath": "%USERPROFILE%\\.dotnet\\tools\\dotnet-lambda-test-tool-8.0.exe" } } }

C# executable assembly

Using the C# 9's top-level statements feature, you generate an executable assembly which will be run by the Lambda. You provide Lambda only with the name of the executable assembly to run.

var handler = async (string argument1, ILambdaContext context) => { }; // bootstrap the Lambda runtime and pass it the handler method await LambdaBootstrapBuilder.Create(handler, new DefaultLambdaJsonSerializer()).Build().RunAsync();

To debug locally you have to create the debug configuration file for you lambda.

Properties\launchSettings.json

{ "profiles": { "Mock Lambda Test Tool": { "commandName": "Executable", "commandLineArgs": "--port 5050", "executablePath": "%USERPROFILE%\\.dotnet\\tools\\dotnet-lambda-test-tool-8.0.exe", "workingDirectory": ".\\bin\\$(Configuration)\\net8.0", "environmentVariables": { "AWS_LAMBDA_RUNTIME_API": "localhost:5050", "AWS_PROFILE": "MyProfile", "AWS_REGION": "us-east-1" } } } }

Handle Enums in the input arguments of .NET AWS Lambda Functions

Function.cs

// create a serializer to handle enums public class LambdaEnumSerializer : DefaultLambdaJsonSerializer { public LambdaEnumSerializer()  : base(options => options.Converters.Add(new JsonStringEnumConverter())) { } } // then use it [assembly: LambdaSerializer(typeof(LambdaEnumSerializer))] // OR use a stream as input argument and deserialize it handling enums public string FunctionHandler(Stream input, ILambdaContext context) { var options = new JsonSerializerOptions { PropertyNameCaseInsensitive = true, Converters = { new JsonStringEnumConverter() } }; JsonSerializer.Deserialize<MyClass>(input, options); }

Logging

Lambda pushes logs to the CloudWatch Logs service under /aws/lambda/[FunctionName].
Permissions (function's execution role, ex: AWSLambdaBasicExecutionRole policy):

• create CloudWatch groups
• create CloudWatch streams
• write log events

• Logs are organized into groups (1 group per function)
  • each group contains a collection of streams (1 stream per function instance) YYYY/MM/DD[Function version][Execution env GUID]

LambdaLogger.Log("Message");

Deployment

dotnet lambda deploy-function [AssemblyName] --profile [Profile]

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); }

Errors

Could not find the specified handler assembly with the file name LambdaTest

The Lambda on AWS has wrongly set the handler to LambdaTest.
AWS - Lambda - Functions - select your function - Code tab - Runtime settings - Edit - change the Handler

Your function doesn't have permission to write to Amazon CloudWatch Logs

1. AWS → IAM → Roles → [the roles used by your lambda] → Persissions policies → Add permission → Create inline policy
2. Service = CloudWatch Logs
3. All CloudWatch Logs actions (logs:*)
4. All Resources