aliases-intro.md

Introduction to AWS Lambda Aliases

You can create one or more aliases for your Lambda function. An AWS Lambda alias is like a pointer to a specific Lambda function version. For more information about versioning, see Introduction to AWS Lambda Versioning.

By using aliases, you can access the Lambda function an alias is pointing to (for example, to invoke the function) without the caller having to know the specific version the alias is pointing to.

AWS Lambda aliases enable the following use cases:

• Easier support for promotion of new versions of Lambda functions and rollback when needed – After initially creating a Lambda function (the $LATEST version), you can publish a version 1 of it. By creating an alias named PROD that points to version 1, you can now use the PROD alias to invoke version 1 of the Lambda function.

  Now, you can update the code (the $LATEST version) with all of your improvements, and then publish another stable and improved version (version 2). You can promote version 2 to production by remapping the PROD alias so that it points to version 2. If you find something wrong, you can easily roll back the production version to version 1 by remapping the PROD alias so that it points to version 1.

• Simplify management of event source mappings – Instead of using Amazon Resource Names (ARNs) for Lambda function in event source mappings, you can use an alias ARN. This approach means that you don't need to update your event source mappings when you promote a new version or roll back to a previous version.

Both the Lambda function and alias are AWS Lambda resources, and like all other AWS resources they both have unique ARNs. The following example shows a Lambda function (the $LATEST version), with one published version. Each version has an alias pointing to it.

You can access the function using either the function ARN or the alias ARN.

• Because the function version for an unqualified function always maps to $LATEST, you can access it using the qualified or unqualified function ARN. The following shows a qualified function ARN with the $LATEST version suffix.

  arn:aws:lambda:aws-region:acct-id:function:helloworld:$LATEST
  

• When using any of the alias ARNs, you are using a qualified ARN. Each alias ARN has an alias name suffix.

  arn:aws:lambda:aws-region:acct-id:function:helloworld:PROD
  arn:aws:lambda:aws-region:acct-id:function:helloworld:BETA
  arn:aws:lambda:aws-region:acct-id:function:helloworld:DEV
  

AWS Lambda provides the following API operations for you to create and manage aliases:

• CreateAlias
• UpdateAlias
• GetAlias
• ListAliases
• DeleteAlias

Example: Using Aliases to Manage Lambda Function Versions

The following is an example scenario of how to use versioning and aliases to promote new versions of Lambda functions into production.

Initially, you create a Lambda function.
The function you create is the $LATEST version. You also create an alias (DEV, for development) that points to the newly created function. Developers can use this alias to test the function with the event sources in a development environment.

You then test the function version using event sources in a beta environment in a stable way, while continuing to develop newer versions.
You publish a version from the $LATEST and have another alias (BETA) point to it. This approach allows you to associate your beta event sources to this specific alias. In the event source mappings, use the BETA alias to associate your Lambda function with the event source.

You then promote the Lambda function version in production to work with event sources in production environment.
After testing the BETA version of the function, you can define the production version by creating an alias that maps to version 1. In this approach, you point your production event sources to this specific version. You do this by creating a PROD alias and using the PROD alias ARN in all of your production event source mappings.

You continue development, publish more versions, and test.
As you develop your code, you can update the $LATEST version by uploading updated code and then publish to beta testing by having the BETA alias point to it. This simple remapping of the beta alias lets you put version 2 of your Lambda function into beta without changing any of your event sources. This approach is how aliases enable you to control which versions of your function are used with specific event sources in your development environment.

If you want to try creating this setup using the AWS Command Line Interface, see Tutorial: Using AWS Lambda Aliases.