modules\aws-demo-environment\main.tf

...  
resource "aws_instance" "nginx" {

  count = "${var.demo_env_nginx_count}"
  connection {
    # The default username for our AMI, and use our on the fly created 
    # private key to do the initial bootstrapping (install of nginx)
    user        = "ubuntu"
    private_key = "${tls_private_key.nginx-provisioner.private_key_pem}"
  }

  instance_type = "t2.micro"
  ami           = "${data.aws_ami.ubuntu.id}"
  key_name      = "${aws_key_pair.nginx-provisioning.id}"
  vpc_security_group_ids = ["${aws_security_group.nginx-sg.id}"]
  # We're going to launch into the same single (public) subnet as our ELB. 
  # In a production environment it's more common to have a separate 
  # private subnet for backend instances.
  subnet_id     = "${aws_subnet.public.id}"

  # We run a remote provisioner on the instance after creating it.
  # In this case, we just install nginx and start it. By default,
  # this should be on port 80
  provisioner "remote-exec" {
    inline = [
      "sudo apt-get -y update",
      "sudo apt-get -y install nginx",
      "sudo sed -i 's/nginx\\!/nginx - instance ${count.index + 1}/g' /var/www/html/index.nginx-debian.html",
      "sudo systemctl start nginx",
    ]
  }
}
...