Lambda & Serverless Apps

Question 1

Explain the AWS Lambda Pricing structure?

Answer 1

• Pay per request and compute time (how long does the function run)
• Pay per calls
  
  • Free tier of 1,000,000 AWS Lambda requests
  • After the free tier you pay $0.20 per 1 million requests
• Pay per duration (in increments of 100ms)
  
  • 400,000 GB/s of compute time = free
  • == 400,000 seconds if function is 1 GB of RAM
  • == 3,200,000 seconds if function is 128 MB RAM
  • After that its $1.00 for 600,000 GB-seconds

Question 2

How does lambda support multi-header values?

Answer 2

• There is a setting on the Application Load Balancer (ALB) that supports this function.
• When enabled, HTTP headers and query string parameters that are sent with multiple values are shown as arrays within the AWS lambda event and reponse objects.

Question 3

What provides permission to invoke a function?

Answer 3

IAM Resource Policy

This is used when another SERVICE triggers the lambda fuction

Question 4

What provides permissions for what a function can do?

Answer 4

IAM Execution Role

Question 5

What are some recommendations for structuring your Lambda functions?

Answer 5

• Seperate business logic from the handle method
• Minimize the dependencies

Question 6

What are some recommendations/best practices for managing serverless applications in AWS?

Answer 6

• Use a serverless application framework.
• Use a SAM template to deploy your serverless applications rather than creating a template in AWS CloudFormation.

Question 7

What are some recommendations/best practices for organizing your code repository for serverless applications?

Answer 7

Organize your functions into services and give each service one deployment template and one code repository.

Question 8

What are some reccommendation(s) / best practices for structuring your development environment for serverless applications?

Answer 8

• Create seperate AWS accounts for each developer if you have management processes in place to handle it.
• Seperate your production and non-production environemnts into different accounts.

Question 9

What is the recommended test heirarchy for serverless applications?

Answer 9

1. Local testing
2. Remote integration tests
3. Automated ntegration tests

Question 10

What are some strategies for mocking out external services that your lambda function is talking to in order to isolate it and be able to test locally?

Answer 10

• Use an exisiting mock library project like DynamoDB local or LocalStack
• Create custom mocks
• Don’t mock - use actual services

Question 11

Why would you use a custom mocking strategy to help unit test your lambda function?

Answer 11

• Allows you to effectively test Lambda functions chained together through multiple services
• Note: This is expensive (lots of work on devs part)

Question 12

How can you debug your serverless application?

Answer 12

Use your IDE debugger on the Docker container provided by SAM CLI

Question 13

What is the difference between a language and runtime in AWS lambda?

Answer 13

• The language is the specific language being used (i.e. Python, NodeJs etc) and runtime is the specifi version of that language.
• As a developer you need to be sure that the runtime is compatible with AWS lambda.

Question 14

What are the size limitations of lambda?

Answer 14

• Uncompressed code and dependencies < 250 MB
• Compressed function package < 50 MB
• Total function packags in a region < 75 GB

Question 15

What are some workarounds for Lambda size limitations?

Answer 15

• Look for smaller libraries.
• Look to break down your function further into smaller steps.
• A different language that offers a more compact solution.

Question 16

What is the Ephemeral storage limitation of lambda?

Answer 16

• < 512 MB
• this is also refered to as the /tmp folder.

Question 17

What is the maximum execution duration for a lambda function?

Answer 17

< 900 seconds (15 minutes)

Question 18

What is the maximum number of concurrent lambda functions you can have?

Answer 18

• You are limited to running 1000 lambda functions @ the same time.
• Can set max limit to something lower using ‘reserved concurrency’ . This is recommended. When this limit is reached then throttling will occur.

Question 19

What is Lambda @Edge?

Answer 19

• Used with CloudFront distribution
• Can modify requests coming from either user or origin

Question 20

What services are asynchronous as it relates to lambda?

Answer 20

• S3
• SNS
• CloudWatch Events / EventBridge
• CodeCommit
• CodePipeline

Question 21

What is a key characteristic of a serverless function?

Answer 21

It runs in response to events that trigger it.

Question 22

What AWS service can be used to trigger Lambda on a schedule?

Answer 22

CloudWatch

Question 23

What two arguments does a Lambda handler require?

Answer 23

event, context

Question 24

Records of Lambda function run logs are stored where?

Answer 24

CloudWatch

Question 25

What should a lambda function package contain?

Answer 25

Your function code and non-included libraries

Question 26

What is event source mapping is AWS lambda?

Answer 26

* Records need to be polled from the source. * Events are read, and these events invoke a lambda function. * Used to process items from a ***stream*** or ***queue*** in services that don't invoke Lambda functions directly.

Question 27

Is event mapping for AWS lambda synchronous or asynchronous?

Answer 27

synchronous

Question 28

How are event source mappings read from a stream or queue?

Answer 28

* In batches * includes multiple items in the event that your function receives. * You can configure the size of the batch that the event source mapping sends to your function, up to a maximum that varies by service. * The number of items in the event can be smaller than the batch size if there aren't enough items available, or if the batch is too large to send in one event and has to be split up.

Question 29

What services are used in event-mapping for AWS lambda?

Answer 29

* Kinesis Data Streams * SQS and SQS FIFO Queues * DynamoDB Streams This list can be broken into 2 categories: Streams and Queues

Question 30

Can the number of item in an event mapping be smaller than the batch size?

Answer 30

* Yes, when the # of items are smaller than the batch size thats OK, or * if the batch is too large to send in one event and has to be split up.

Question 31

What are AWS Lambda Destinations?

Answer 31

* allows you to route asynchronous function results as an execution record to a destination resource without writing additional code. * Previously, you needed to write the SQS/SNS/EventBridge handling code within your Lambda function and manage retries and failures yourself. * Destinations provide more useful capabilities over Dead Letter queues for asynchronous failure situations by passing additional function execution information, including code exception stack traces, to more destination services.

Question 32

How do you allow lambda functions access to VPC resources?

Answer 32

* You must define a VPC ID, the subnets and the securty groups * Lambda will create an ENI (Elastic Network Interface) in your subnet(s) * AWSLambdaVPCAccessExecutionRole is needed to create the ENI

Question 33

Do lambda functions inside a VPC have access to the public internet?

Answer 33

* Not by default. * Deploying a lambda funciton in a public subnet does NOT give the function internet access or public IP. * To give a lmbda function in a VPC internet access you must deploy it in a PRIVATE subnet and set up a NAT Gateway / Instance to provide internet access.

Question 34

If you have a computation heavy function, how can you increase that lambda functions performance?

Answer 34

* Increase the RAM * Increasing the RAM increases the vCPU credits. * Should also decrease the duration of the function. * Note: The more memory you use the more you will pay so find a balance.

Question 35

If you have a function / job that runs for 15 minutes or more, is lambda the best service to use to run that function?

Answer 35

No. Lambda functions should run no more then 15 minutes. Other AWS services such as Fargate, ECS or EC2 would be a better option.

Question 36

Should ***connections*** to clients (RDS, SDK, etc.) be formed within a handler method, or outside of the handler method?

Answer 36

Outside the handler method. This way it only makes the connection once, ad the execution context will keep that connection alive for subsequent calls.

Question 37

Explain Lambda Versions

Answer 37

* A new version of lambda is created each time a new function is published. * Versions are immutable.

Question 38

Explain lambda aliases

Answer 38

Aliases are mutable and point to an immutable version.

Question 39

Can a lambda alias point to another lambda alias?

Answer 39

No. An Alias can only point to a lambda version.

Question 40

What is the maximum size of environment variables in lambda?

Answer 40

4kb

Question 41

What is the min and max memory allocation sizes for lambda?

Answer 41

128kb - 10GB (64 MB increments)

Question 42

How do you declare a Lambda function with AWS CloudFormation?

Answer 42

* Upload all the code as a zip to S3 and refer to the object in the cloudFormation's AWS::Lambda::Function block. * Can also be refered to inline with CloudFormation but that only applies to simple functions that do not require any external dependencies.

Question 43

How can a Lambda function be integrated with an ALB?

Answer 43

With a target group

Question 44

What is the best way to send the result of an asynchronous Lambda function to SQS?

Answer 44

Use a destination

Question 45

What is AWS SAM?

Answer 45

* Serverless Application Model * Its a framework for developing and deploying serverless applications. * Refered to as an AWS CLI tool and CloudFormation Macro --\> * All configurations are in YAML code which gets compiled into a complex CloudFormation Template. * Requires only 2 commands to deploy to AWS * Can help you run Lambda, API Gateway, DynamoDB locally

Question 46

What header indicates that something is a SAM template?

Answer 46

A Transform Header: ex. Transform: 'AWS::Serverless-2016-10-31'

Question 47

What are the three resources that you can bring into your code using a SAM template?

Answer 47

* Lambda Functions -\> AWS : : Serverless : : Function * API Gateway -\> AWS : : Serverless : : Api * DynamoDB -\> AWS : : Serverless : : SimpleTable

Question 48

How do you package and deploy a SAM application?

Answer 48

* AWS CloudFormation package using the CLI or SAM package * To deploy use cloudFormation deploy / sam deploy

Question 49

What is a Cloud Development Kit (CDK)?

Answer 49

* Allows you to write Infrastructure as Code (IaC) using an imperative paradigm with your favorite language. * CDK transpiles into CloudFormation templates.