使用方法：Sub 或：Join in "AWS::CloudFormation,:Init", file key

Question

I'm currently creating a yaml template and I'm trying to modularize templates so that they can be re-used across different projects. The issue I'm having is that I keep getting syntax errors if I try to use.Join or !Sub in file name.

files: 
 /tmp/myfile2.txt: 
   content: "/tmp/myfile1.txt"
   mode: "120644"

I want to create a project specific directory instead of /tmp/, for example:

files: 
  /PROJECT_NAME/myfile2.txt: 
    content: "/tmp/myfile1.txt"
    mode: "120644"

PROJECT_NAME being a CloudFormation parameter.

Is it possible to achieve something like this:

files: 
  !Sub "/${PROJECT_NAME }/myfile2.txt": 
    content: |
      some shell commands
      some shell commands
      some shell commands
    mode: "120644"

I tried multiple ways of achieveing this, using,Join: Fn:,Sub. !Sub.

Just wondering if anyone had done anything like this before?

Thank you!

Answer 1

Just wondering if anyone had done anything like this before?

Many people tried and filed. The reason is that you can't use non-strings as maps in CloudFormation. From CFN format specification :

A map is a collection of key-value pairs, where the keys are always strings .

Therefore, a proposed solution is to use UserData to define the dynamically generate file, instead of using CFN metadata.