Hetzner Cloud terraform coreos install

ignition.json

{
  "ignition": {
    "version": "2.0.0",
    "config": {}
  },
  "storage": {
  },
  "systemd": {},
  "networkd": {},
  "passwd": {
    "users": [
      {
        "name": "core",
        "sshAuthorizedKeys": [
          "<your public key>"
        ]
      }
    ]
  }
}

install.sh

#!/usr/bin/env sh

set -e

wget https://raw.github.com/coreos/init/master/bin/coreos-install
chmod +x coreos-install
./coreos-install -d /dev/sda -i /root/ignition.json
reboot

main.tf

provider "hcloud" {
  token = "<token>"
}

resource "hcloud_ssh_key" "notebook" {
  name = "nschieder@notebook"
  public_key = "${file("~/.ssh/id_ed25519.pub")}"
}

resource "hcloud_server" "master" {
  name = "master"
  image = "debian-9"
  server_type = "cx11"
  ssh_keys = ["${hcloud_ssh_key.notebook.id}"]
  datacenter = "fsn1-dc8"
  rescue = "linux64"

  connection {
    host = "${hcloud_server.master.ipv4_address}"
    timeout = "1m"
    agent = false
    private_key = "${file("~/.ssh/id_ed25519")}"
  }

  provisioner "file" {
    source      = "ignition.json"
    destination = "/root/ignition.json"
  }

  provisioner "remote-exec" {
    script = "install.sh"
  }

  provisioner "remote-exec" {
    connection {
      host = "${hcloud_server.master.ipv4_address}"
      timeout = "1m"
      agent = false
      private_key = "${file("~/.ssh/id_ed25519")}"
      user = "core"
    }
    inline = "sudo hostnamectl set-hostname ${hcloud_server.master.name}"
  }
}

resource "hcloud_server" "node1" {
  name = "node1"
  image = "debian-9"
  server_type = "cx11"
  ssh_keys = ["${hcloud_ssh_key.notebook.id}"]
  datacenter = "fsn1-dc8"
  rescue = "linux64"

  connection {
    host = "${hcloud_server.node1.ipv4_address}"
    timeout = "1m"
    agent = false
    private_key = "${file("~/.ssh/id_ed25519")}"
  }

  provisioner "file" {
    source      = "ignition.json"
    destination = "/root/ignition.json"
  }

  provisioner "remote-exec" {
    script = "install.sh"
  }

  provisioner "remote-exec" {
    connection {
      host = "${hcloud_server.node1.ipv4_address}"
      timeout = "1m"
      agent = false
      private_key = "${file("~/.ssh/id_ed25519")}"
      user = "core"
    }
    inline = "sudo hostnamectl set-hostname ${hcloud_server.node1.name}"
  }
}

@thetechnick Understood, thanks for offering some context (and thanks for this gist!). My current solution also uses null_resource, although properly tainting an existing server resource and applying changes is still a pain. Once I figure that part out I'll link a gist to it here.