How to set the administrator password for a Windows Server machine on AWS from CloudFormation? [closed]

Answer 1

Based on the comments.

The solution was to use the following command in UserData:

net user Administrator "new_password"

The command, as explained in the docs, can be used to change admin password.

This works because UserData executes under administrator account (ref):

User data scripts are executed from the local administrator account when a random password is generated.

Answer 2

For completeness and future reference, here's what the CloudFormation template now looks like:

"UserData": {
    "Fn::Base64": {
        "Fn::Join": [
            "",
            [
            "<powershell>\n",
            "net user Administrator ",
            {
                "Ref": "Password"
            },
            "\n",
            "& \"C:\\Program Files\\Amazon\\cfn-bootstrap\\cfn-signal\"",
            " --stack ", { "Ref": "AWS::StackName" },
            " --resource MyInstance" ,
            " --region ", { "Ref" : "AWS::Region" }, 
            "\n",
            "</powershell>\n"
            ]
        ]
    }
},
"CreationPolicy": {
    "ResourceSignal" : {
        "Count": "1",
        "Timeout": "PT15M"
        }
    }
}

So there's two things going on:

• I am changing the Administrator password as suggested by Marcin in his answer.
• I am using cfn-signal and CreationPolicy to ensure that the CloudFormation deployment waits for the UserData to be completed. More details here.