在引导新 EC2 实例时使用 UserData 中的内部函数

Question

I have written cloudformation which consists of an EC2 instance and a RDS database. I wish to get the endpoint address from the RDS, which i can via the intrinsic function GetAtt, and pass it into the EC2 instance in a text file. Below is the code i've tried however its not working and giving me what i want.

Resources:
MyEC2Instance:
Type: AWS::EC2::Instance
Properties:
    ImageId: ami-74e6b80d
    InstanceType: t2.nano
    SecurityGroups:
      - Ref: MySecurityGroup
    KeyName:
      - Ref: MyKeyPair
    UserData:
      Fn::Base64:
        Fn::Sub:
          - |
            #!/bin/bash
            touch /home/ubuntu/touch1.txt
          - DatabaseAddress: !GetAtt MyDatabase.Endpoint.Address
            echo "My address is ${DatabaseAddress}" >> touch1.txt
    DependsOn: MyDatabase

Answer 1

You can fetch attributes from a resource without the use of GetAtt while in a Sub function.

Example:

UserData:
  Fn::Base64:
    Fn::Sub:
      - |
        #!/bin/bash
        touch /home/ubuntu/touch1.txt
        echo "My address is ${MyDatabase.Endpoint.Address}" >> /home/ubuntu/touch1.txt