Fn::Sub

Use Fn::Sub to perform string substitution. Consider the following code:

DSN: "Fn::Sub"
  - mysql://${db_user}:${db_pass}@${db_host}:3306/wordpress
  - { db_user: lchan, db_pass: ch33s3, db_host: localhost }

This would yield the following value:

mysql://lchan:ch33s3@localhost:3306/wordpress

When you combine these functions with Ref and Fn::GetAtt, you can start doing some really powerful stuff, as we'll see in the recipes throughout this book.

Other available built-in functions include the following:

  • Fn::Base64
  • Fn::FindInMap
  • Fn::GetAZs
  • Fn::ImportValue
  • Fn::Select
Documentation on all of these functions is available at http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference.html.
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