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lambda.md

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Lambda

Overview

  • pay per request and compute time

Configuration

  • timeout: default 3 seconds, maximum 15 minutes
  • Environment variables
  • allocated memory (128MB to 3G)
  • ability to deploy within a VPC + assign security groups
  • IAM execution role must be attached to the Lambda function
  • tracing with AWS X-Ray ⇒ enable active tracing will automatically adds X-Ray permission

Concurrency and Throttling

  • concurrency up to 1000 executions (can increase through ticket) (standard concurrency)
  • can set a "reserved concurrency" at the function level (maximum concurrency that function can reach)
  • can set "provisioned concurrency"
  • each invocation over the concurrency limit will trigger a "Throttle"
  • Throttle behavior:

    • if synchronous invocation ⇒ return ThrottleError - 429 (eg: http request)

    • If asynchronous invocation ⇒ retry automatically twice and after all retries, then go to DLQ (eg: S3 trigger)

      • DLQ can be a SNS topic or SQS queue

      ⇒ debug in production

Limitation

  • Execution:
    • Memory allocation: 128MB - 3008MB
    • Maximum execution time: 15 minutes
    • Disk capacity (in /tmp): 512MB
    • Concurrency limits: 1000
  • Deployment:
    • install the dependencies packages and zip with code
      • libraries need to be compiled on Amazon Linux
    • Lambda function deployment size (compressed): 50MB
      • if > 50MB, use S3
    • Uncompressed deployment: 250MB
    • can use /tmp directory to load other file at startup
    • size of environment variables: 4KB

Versions vs Aliases

Version

  • publish a Lambda function ⇒ create a version
  • versions are immutable
  • versions have their own ARN
  • version = code + configuration

Alias

  • aliases are pointers to Lambda function versions
  • can define a "dev", "test", "prod" aliases and point to different lambda versions
  • aliases are mutable
  • enable Blue / Green deployment by assigning weights to versions
  • aliases have their own ARNs

Using with CloudFormation

  • store the Lambda zip in S3
  • refer S3 zip location in the CloudFormation code

/tmp space

  • use cases:
    • if your Lambda function needs to download a big file to work
    • if your Lambda function needs disk space to perform operations
  • max size is 512MB
  • The directory content remains when the execution context is frozen, providing transient cache that can be used for multiple invocations
  • For persistence of object (non temporary), use S3

Best practices

  • perform heavy-duty work outside of your function handler, function will reuse it
    • connect to databases
    • initialize the AWS SDK
    • pull in dependencies or datasets
  • use environment variables
    • database connection string, S3 bucket...
    • password, sensitive value... encrypt using KMS
  • minimize deployment package size
    • break down the function
    • the Lambda zip limit
  • avoid using recursive code, never have a Lambda function call itself ⇒ the bill will increase
  • don't put Lambda function in VPC unless you have to ⇒ initialize speed will increase

Read more: AWS Serverless Lambda functions best practice

Lambda@Edge

  • use Lambda@Edge deploy Lambda functions alongside your CloudFront CDN

    ⇒ deploy Lambda globally

  • can use Lambda to change CloudFront request and responses:

    • after CloudFront receives a request from a viewer (viewer request)
    • before CloudFront forwards the request to the origin (origin request)
    • after CloudFront receives the response from the origin (origin response)
    • before CloudFront forwards the response the the viewer (viewer response

    CloudFront Request

    • can generate responses to viewers without ever sending the request to the origin

  • global application

    Global Application

  • Use cases:

    • Website Security and Privacy
    • Dynamic Web App at the Edge
    • Search Engine Optimization (SEO)
    • Intelligently Route Across Origins and Data Centers
    • Bot Mitigation at the Edge
    • Real-time Image Transformation
    • A/B Testing
    • User Authentication, Authorization
    • User Prioritization
    • User Tracking and Analytics