Aws

AWS announced full featured redirection support for Application Load Balancers in the summer of 2018, but it lacked support for CloudFormation initially. Since I really like doing as much as I can with CloudFormation, I tossed around ideas for how to still get a redirection rule into an ELBv2 and settled on using Lambda and CloudFormation custom resources.

AWS announced full featured redirection support for Application Load Balancers. This solves one of the long standing problems with web applications—HTTP to HTTPS redirection.

This article aims to demonstrate some of the many uses of the Fn::Sub syntax in the AWS CloudFormation service. Topics include:

• Basic Fn::Sub and !Sub syntax
• Short and long form syntax
• Nested Sub and ImportValue statements

Background

About a year ago (Sept 2016, along with YAML support) AWS added a new intrinsic function to CloudFormation: Fn::Sub. This greatly improved string concatenation in CloudFormation.