Tutorial: AWS Certified Developer - Associate (DVA-C02)

Lambda versions and aliases

Concepts

When you create a Lambda function, you are actually creating version one. Every time you update your Lambda function, a new version can be published. Each version is a snapshot of your function code and configuration at the time of publishing. Versions are immutable, which means once a version is published, the code and configuration cannot be changed.

Each Lambda function version has a unique Amazon Resource Name (ARN) and can be accessed independently. When you publish a new version, AWS Lambda copies the latest version of your function into a new version with a unique ARN.

Example: Publishing a Lambda Version

aws lambda publish-version --function-name MyFunction

This command publishes a new version of the Lambda function named “MyFunction”.

Lambda Aliases

Aliases are like pointers or references to Lambda function versions. An alias points to a specific Lambda function version, and you can change the version it points to at any time. Therefore, aliases enable you to abstract the function invocation from the version, and they facilitate simplified blue-green deployments or A/B testing.

An alias can also have a description and can be mapped to function version weights, which is useful for gradually shifting traffic from one version to another, often referred to as “weighted aliases”.

Example: Creating an Alias for a Specific Version

aws lambda create-alias \ --function-name MyFunction \ --name PROD \ --function-version 1 \ --description "Production environment alias"

This command creates an alias named “PROD” that points to version 1 of the “MyFunction” Lambda function.

Example: Updating an Alias to Point to a New Version

aws lambda update-alias \ --function-name MyFunction \ --name PROD \ --function-version 2

This command updates the “PROD” alias to point to version 2 of the “MyFunction” Lambda function.

Lambda Versioning and Aliasing Best Practices

Versioning: Create a new version only for code changes that you want to roll out. Use the $LATEST version for development and testing.
Aliases: Create aliases that represent environments (e.g., DEV, TEST, PROD) and use them in your deployment pipelines.
Immutable Code: Treat your Lambda versions as immutable. Once you have tested a Lambda version and are satisfied with its stability, publish it.
Weighted Aliasing: Use weighted aliases to gradually introduce new versions. This helps in reducing the risk of new deployments.
Traffic Shifting: Utilize Lambda’s built-in traffic shifting capabilities for canary deployments or rolling updates.

Summary of Lambda Versions and Aliases

Feature	Purpose	Characteristics
Versions	Manage different sets of code/configurations	Immutable and have a unique ARN
Aliases	Reference to a specific version	Mutable and can have weighted distributions

Using versions and aliases provides a structured way to manage deployments and roll back to previous versions if necessary. It is an integral part of a mature CI/CD pipeline in the context of serverless architectures provided by AWS Lambda.

As part of the AWS Certified Developer – Associate (DVA-C02) exam preparation, understanding the intricacies of Lambda versions and aliases is essential, as they are fundamental components for managing function deployment and lifecycle within the AWS ecosystem.

Answer the Questions in Comment Section

T/F: AWS Lambda aliases can be used to split traffic between two different Lambda function versions.

Answer: True

Explanation: AWS Lambda aliases support traffic shifting between two Lambda function versions. This allows for gradual deployment strategies such as canary releases or blue/green deployment.

T/F: Once you publish a new version of a Lambda function, the old versions are deleted automatically.

Answer: False

Explanation: AWS Lambda retains old versions after you publish a new one. You are not required to delete old versions and they can be invoked using the version-specific ARN if needed.

When linking an AWS Lambda alias to a function version, which of the following information is necessary?

A) The name of the Lambda function
B) The maximum execution time of the Lambda function
C) The specific version number of the Lambda function
D) The memory allocated to the Lambda function

Answer: A and C

Explanation: When creating an alias, you need to specify the name of the Lambda function and the specific version number that the alias should point to.

To which of the following can an AWS Lambda alias point?

A) Another alias
B) A Lambda function version
C) A Lambda function ARN
D) An S3 bucket

Answer: B

Explanation: An AWS Lambda alias can only point to a specific Lambda function version, not to another alias, an entire function ARN without a version, or any external AWS resource like an S3 bucket.

T/F: Each AWS Lambda function can have multiple aliases, but an alias can only point to one Lambda function version at a time.

Answer: True

Explanation: A function can have multiple aliases, each used for different purposes (e.g., development, testing, production), but an alias can only point to one function version at any moment.

T/F: When you update the Lambda function code, all aliases pointing to the $LATEST version will automatically point to this new code.

Answer: True

Explanation: Aliases that point to the $LATEST version are updated automatically when new code is uploaded because $LATEST refers to the most recent deployment.

Which of the following can you specify when you create an AWS Lambda alias?

A) Memory size
B) Environment variables
C) Description
D) Timeout settings

Answer: C

Explanation: When creating an alias, you can specify a description for it, but memory size, environment variables, and timeout settings are defined on the function or version level.

T/F: Lambda aliases can have their own resource-based IAM policies.

Answer: True

Explanation: AWS Lambda aliases can have resource-based policies, making it possible to grant permissions to invoke the alias while maintaining different permissions for the underlying Lambda function and other aliases.

How can weight be assigned to different Lambda function versions when using aliases for traffic shifting?

A) Through the AWS Management console
B) Using AWS CLI commands
C) By modifying the Lambda function code
D) Through environment variables

Answer: A and B

Explanation: Traffic weights can be assigned and adjusted for Lambda function versions through the AWS Management console or using AWS CLI commands; it’s not handled by Lambda function code or environment variables.

T/F: It’s possible to automatically revert to the old version of a Lambda function if an error rate increases after deployment.

Answer: False

Explanation: AWS Lambda does not automatically revert to a previous version based on the error rate. Any rollback strategy must be implemented manually or through an automated process outside of the Lambda service.

Which of the following AWS Lambda alias update is likely to cause an error?

A) Changing the alias description
B) Changing the alias to point to a different version
C) Updating the Lambda function code
D) Overwriting an existing alias with a new one without version change

Answer: D

Explanation: Overwriting an existing alias with a new one when the alias’s version isn’t changed is likely to cause errors. Aliases are expected to have unique names and overwriting without a version change may confuse clients using the alias if it points to the same version as before.

When should you use AWS Lambda aliases?

A) When you want to modify the runtime configuration of a Lambda function
B) When you have multiple versions of a Lambda function and want to control access to them
C) To create a secure backup of a Lambda function
D) To save costs by sharing the same Lambda execution role across multiple functions

Answer: B

Explanation: Lambda aliases are ideal for managing access and directing traffic to multiple versions of a Lambda function. They are not for modifying runtime configuration, creating backups, or sharing an execution role across functions.