Referencing Terraform instance attributes to user data during creation of EC2-CodePudding

How can I pass the public_dns value of the aws_instance resource to the user_data section ?

resource "aws_instance" "app_server" {
  ami                    = "ami-04ad2567c9e3d7893"
  instance_type          = "t2.micro"
  vpc_security_group_ids = [aws_security_group.web-sg.name]


  user_data = <<-EOF
                  #!/bin/bash
                  sudo su
                  echo "<p> The Public DNS of instance: ${self.app_server.public_dns} </p>" >> index.html
                  python -m SimpleHTTPServer 80
                  EOF
  tags = {
    Name = "web_instance"
  }

}

I tried with self or with aws_instance.app_server.public_dns declaration but none of them worked with getting the following error.

CodePudding user response：

The public dns will become available after the instance has started. It isn't possible to reference it in user data. You can read it though with this command:

curl http://169.254.169.254/latest/meta-data/public-hostname