Developing Solutions with AWS Lambda

Question 1

What is AWS Lambda

Answer 1

Key concept : Serverless

AWS Lambda is a compute service that enables you to run code without provisioning or managing servers. You pay only for the compute time you consume—there is no charge when your code is not running.

The code you run on AWS Lambda is uploaded as a “Lambda function”

The code must be written in a “stateless” style i.e. it should assume that there is no affinity to the underlying compute infrastructure

Question 2

Anatomy of a Lambda function

Answer 2

• Handler : When a Lambda function is invoked, code execution begins at what is called the handler. The handler is a specific code method (Java, C#) or function (Node.js, Python) that you’ve created and included in your package.
• Event object : One of the parameters provided to your handler function is an event object. The contents of the event parameter include all of the data and metadata your Lambda function needs to drive its logic.
• Context object : The context object allows your function code to interact with the Lambda execution environment. Content and structure vary, at minimum it will contain :
  
  • AWS RequestId
  • Timeout -> maximum of 900 seconds
  • Logging -> to stream log statements to Amazon CloudWatch Logs

Question 3

How to package in Python, Java, C#

Answer 3

• Node.js, Ruby, and Python
  To create a Lambda function, you first create a Lambda function deployment package, a .zip file consisting of your code and any dependencies. Use npm or pip to install libraries. All dependencies must be at root level.

- Java
Your deployment package can be a .zip file or a standalone jar; it is your choice. Use Maven or IDE plugins. Compiled class and resource files at root level, required jars in /lib directory.

• C#
  A .NET Core Lambda deployment package is a zip file of your function’s compiled assembly along with all of its assembly dependencies. Use Nuget or VisualStudio plugins. All assemblies (.dll) at root level.

Question 4

The three ways to deploy an AWS Lambda function

Answer 4

• If your code does not require custom libraries (other than the AWS SDK), edit your code inline through the AWS Management Console. The console will zip up your code with the relevant configuration information into a deployment package that the Lambda service can run.
• In an advanced scenario where your code requires custom libraries, you can upload a .ZIP file of your code and all of its dependencies through the AWS Management Console or the AWS CLI.
• You can also create your Lambda deployment package (.ZIP) and upload it to an S3 bucket, and AWS Lambda loads your code directly from Amazon S3.

Question 5

The three Lambda execution models

Answer 5

• Synchronous : direct call (ex: from Amazon API Gateway)
• Asynchronous : triggered by events -> Push event model
• Stream-based : triggered by changes (ex: from DynamoDB or Kinesis) -> Pull event model

Question 6

How does the Push event model work

Answer 6

An event source directly invokes a Lambda function when it publishes an event
-> Sources : Amazon S3, Amazon SNS, Amazon Cognito, Amazon Echo, and user applications.

You do not use the AWS Lambda APIs to map your Lambda function to its event source. Instead, you use APIs from the event source to configure this mapping.

Question 7

How does the Pull event model work

Answer 7

In the pull event model, AWS Lambda polls the event source and invokes your Lambda function when it detects an event.
-> Lambda is used for streaming event sources such as Amazon Kinesis and DynamoDB streams.

Lambda provides an API for you to create event source mappings that associate your Lambda function with a specific event source

Question 8

How does the Direct invocation work

Answer 8

It causes AWS Lambda to run the function synchronously and returns the response immediately to the calling application letting you know whether the invocation happened.
It is available for custom applications.

Question 9

Difference between Execution permissions and Invocation permissions

Answer 9

Execution permissions: The permissions that your Lambda function needs to access other AWS resources in your account. Execution roles determine what your function can do.

Invocation permissions: The permissions that the event source needs to communicate with your Lambda function. Invocation roles determine who can run your function

Question 10

Difference between Push and Pull models for invocation permissions

Answer 10

• Push model : grant these event sources permissions to invoke the Lambda function by updating the access policy associated with the Lambda function
• Pull model : grant AWS Lambda permission to read from the stream

Question 11

How does versioning work

Answer 11

Versioning allows you to publish one or more versions of your Lambda function. Each time you publish a version, AWS Lambda copies the $LATEST version (code and configuration) to create a new version.

Question 12

What is an alias

Answer 12

Aliases can be created for Lambda function. An alias is a Lambda resource and has its own unique ARN. An alias is like a pointer to a specific Lambda function version. It allows you to access the Lambda function without having to know the specific version the alias is pointing to.

Question 13

What is a layer

Answer 13

A layer is a ZIP archive that contains libraries, a custom runtime, or other dependencies. With layers, you can use libraries in your function without needing to include them in your deployment package.

A function can use up to 5 layers at a time.

You can create layers, or use layers published by AWS and other AWS customers.

Question 14

Function code best practices

Answer 14

• Separate the Lambda handler (entry point) from your core logic
• Take advantage of execution context reuse to improve the performance of your function
• Use environment variables to pass operational parameters to your function
• Control the dependencies in your function’s deployment package
• Minimize your deployment package size to its runtime necessities
• Minimize the complexity of your dependencies
• Avoid using recursive code
• Share common dependencies with layers

Question 15

Function configuration best practices

Answer 15

• Performance test your Lambda function for memory
• Load test your Lambda function for timeout
• Understand Lambda limits
• Delete Lambda functions that you are no longer using

Question 16

Other best practices (alarms/metrics/asynchronous invokes)

Answer 16

• Alarms and metrics
  Use AWS Lambda metrics and CloudWatch alarms
  Use logging library
• Asynchronous invokes
  Create and use dead-letter queues