AWS Cloudformation：变量未在cfn-init命令中插值

Question

In the following Cloudformation EC2 instance declaration:

  MyInstance:
    Type: AWS::EC2::Instance
    Metadata:
      Comment: Test
      AWS::CloudFormation::Init:
        config:
          commands:
            01_test:
              command: "echo \"${MyEndpoint}\" > /root/test.txt"
              cwd: "~"

The var MyEndpoint is never interpolated (the file created is empty).

Is it a syntax issue?

The variable certainly exists (it is used throughout the rest of the CF template with success)

Answer 1

The above does not work.

One needs to use the !Sub function

  AWS::CloudFormation::Init:
    config:
      commands:
        01_test:
          command:
            !Sub |
              echo ${MyEndpoint} > /root/test.txt