AWS Developer Associate (DVA-C01) Review Material – Lambda and SAM

Lambda

• General
  • A compute service that lets you run code without provisioning or managing servers.
  • Best suited for shorter, event-driven workloads, since Lambda functions run for up to 15 minutes per invocation.
  • Concepts:
    • Function
    • Trigger
    • Event
    • Execution environment
    • Instruction set architecture
    • Deployment package
    • Runtime
    • Layer
    • Extension
    • Concurrency
    • Qualifier
    • Destination
• Can be invoked:
  • Synchronously
    • Event Source Mapping (Lambda pull from services)
      • KDS
      • SQS and SQS FIFO
      • DynamoDB data streams
  • Asynchronously:
    • aws lambda invoke \ –function-name my-function \ –invocation-type Event \ –cli-binary-format raw-in-base64-out \ –payload ‘{ “key”: “value” }’ response.json
    • Uses an internal Event Queue
    • Can point to DLQ for failures.
    • AWS Services that are async:
      • S3
      • SNS
      • EventBridge
• Lambda Destinations
  • For Event Source Mapping – For discarded events
  • For Async – Can replace DLQ
• Lambda Container:
  • Base image must implement Lambda Runtime API
  • Can test locally through an emulator
• Concurrency:
  • Reserved – ensure the max concurrency
  • Provisioned -prepares the no. of concurrent execution of a Lambda funciton.

SAM

• An open-source framework that you can use to build serverless applications on AWS.
• A serverless application is a combination of Lambda functions, event sources, and other resources that work together to perform tasks. Note that a serverless application is more than just a Lambda function—it can include additional resources such as APIs, databases, and event source mappings.
• Components:
  1. AWS SAM template specification
     • AWS SAM templates are an extension of AWS CloudFormation templates, with some additional components that make them easier to work with.
     • Written in YAML
     • Can specify other resources not just Lambda
  2. AWS SAM command-line interface (AWS SAM CLI).
     • sam build
     • aws cloudformation package / sam package
     • awas cloudformation deploy / sam deploy
• Template Anatomy:
  • Transform declaration
    • Transform: AWS::Serverless-2016-10-31
    • Required
  • Globals section:
    • Globals
    •  Defines properties that are common to all your serverless functions and APIs
  • Resources section
    • can contain a combination of AWS CloudFormation resources and AWS SAM resources
    • Resources:
      • AWS::Serverless::Api – Creates a collection of Amazon API Gateway resources and methods that can be invoked through HTTPS endpoints
      • AWS::Serverless::Function – Creates an AWS Lambda function, an AWS Identity and Access Management (IAM) execution role, and event source mappings that trigger the function.
      • AWS::Serverless::SimpleTable – Creates a DynamoDB table with a single attribute primary key. It is useful when data only needs to be accessed via a primary key.
  • Parameters section
    • Objects that are declared in the Parameters section cause the sam deploy --guided command to present additional prompts to the user. 
• Building
  • Gathers the build artifacts of your application’s dependencies and places them in the proper format and location for next steps, such as locally testing, packaging, and deploying.
  • CLI sam build
    • transform SAM template into CloudFormation template together with the application code
• Testing
  • Can invoke your function locally
  • CLI sam local invoke command and providing its function logical ID and an event file
• Packaging
  • Make application available for others to find and deploy
  • CLI aws cloudformation package / sam package
    • zip and upload to S3 bucket
• Deploying
  • Can use CICD. For AWS use CodePipeline
  • CLI awas cloudformation deploy / sam deploy
    • Find the package from S3 and load to CloudFormation
  • Can use CodeDeploy
• SAR
  • Repository for SAM
  • CLI: sam publish
• Policy Templates:
  • S3ReadPolicy
  • SQSPollerPolicy
  • DyanmoDBCrudPolicy