infra/main.tf

@@ -2,6 +2,20 @@
 # (one per server in docs/architecture.md). Each host module owns its own
 # firewall (and volume, where applicable) - see modules/<host>/main.tf.
 
+locals {
+  # SSH to dev/prod is only permitted from the vpn server's public IP: admins must
+  # tunnel through the VPN first, whose egress traffic is then sourced from this IP.
+  # vpn itself can't require tunneling through itself, so it keeps
+  # var.allowed_ssh_source_ips for direct SSH access.
+  vpn_ssh_source_ips = ["${module.vpn.ipv4}/32"]
+
+  # Rendered once and uploaded+run by every host module immediately after its
+  # server is created - see scripts/bootstrap.sh.tftpl.
+  bootstrap_script = templatefile("${path.module}/scripts/bootstrap.sh.tftpl", {
+    deploy_user = var.deploy_user
+  })
+}
+
 module "network" {
   source = "./modules/network"
 
@@ -20,8 +34,10 @@ module "dev" {
   network_id             = module.network.id
   private_ip             = var.dev_private_ip
   volume_size            = var.dev_volume_size
-  allowed_ssh_source_ips = var.allowed_ssh_source_ips
+  allowed_ssh_source_ips = local.vpn_ssh_source_ips
   network_ip_range       = var.network_ip_range
+  bootstrap_script       = local.bootstrap_script
+  ssh_private_key_path   = var.ssh_private_key_path
 
   # module.network.id alone doesn't guarantee the subnet exists yet, and a server
   # can't join a network before it has a subnet.
@@ -38,8 +54,10 @@ module "prod" {
   network_id             = module.network.id
   private_ip             = var.prod_private_ip
   volume_size            = var.prod_volume_size
-  allowed_ssh_source_ips = var.allowed_ssh_source_ips
+  allowed_ssh_source_ips = local.vpn_ssh_source_ips
   network_ip_range       = var.network_ip_range
+  bootstrap_script       = local.bootstrap_script
+  ssh_private_key_path   = var.ssh_private_key_path
 
   depends_on = [module.network]
 }
@@ -52,4 +70,6 @@ module "vpn" {
   location               = var.location
   ssh_key_id             = data.hcloud_ssh_key.main.id
   allowed_ssh_source_ips = var.allowed_ssh_source_ips
+  bootstrap_script       = local.bootstrap_script
+  ssh_private_key_path   = var.ssh_private_key_path
 }

infra/modules/dev/main.tf

@@ -6,7 +6,7 @@
 resource "hcloud_firewall" "this" {
   name = "dev-firewall"
 
-  rule { # server ssh
+  rule { # server ssh - wired to the vpn server's public IP only, see infra/main.tf
     direction  = "in"
     protocol   = "tcp"
     port       = "22"
@@ -61,6 +61,25 @@ resource "hcloud_server" "this" {
     network_id = var.network_id
     ip         = var.private_ip
   }
+
+  connection {
+    type        = "ssh"
+    host        = self.ipv4_address
+    user        = "root"
+    private_key = file(var.ssh_private_key_path)
+  }
+
+  provisioner "file" {
+    content     = var.bootstrap_script
+    destination = "/root/bootstrap.sh"
+  }
+
+  provisioner "remote-exec" {
+    inline = [
+      "chmod +x /root/bootstrap.sh",
+      "/root/bootstrap.sh",
+    ]
+  }
 }
 
 resource "hcloud_volume" "storage" {

infra/modules/dev/variables.tf

@@ -34,7 +34,7 @@ variable "volume_size" {
 }
 
 variable "allowed_ssh_source_ips" {
-  description = "CIDRs allowed to reach port 22 on dev."
+  description = "CIDRs allowed to reach port 22 on dev. Set by the root module to the vpn server's public IP."
   type        = list(string)
 }
 
@@ -42,3 +42,13 @@ variable "network_ip_range" {
   description = "CIDR of the private network, allowed through the firewall for traffic from prod."
   type        = string
 }
+
+variable "bootstrap_script" {
+  description = "Rendered post-install script, uploaded and executed on the server immediately after creation."
+  type        = string
+}
+
+variable "ssh_private_key_path" {
+  description = "Local path to the private key matching var.ssh_key_id, used to run the bootstrap script over SSH."
+  type        = string
+}

infra/modules/prod/main.tf

@@ -5,7 +5,7 @@
 resource "hcloud_firewall" "this" {
   name = "prod-firewall"
 
-  rule { # server ssh
+  rule { # server ssh - wired to the vpn server's public IP only, see infra/main.tf
     direction  = "in"
     protocol   = "tcp"
     port       = "22"
@@ -88,6 +88,25 @@ resource "hcloud_server" "this" {
     network_id = var.network_id
     ip         = var.private_ip
   }
+
+  connection {
+    type        = "ssh"
+    host        = self.ipv4_address
+    user        = "root"
+    private_key = file(var.ssh_private_key_path)
+  }
+
+  provisioner "file" {
+    content     = var.bootstrap_script
+    destination = "/root/bootstrap.sh"
+  }
+
+  provisioner "remote-exec" {
+    inline = [
+      "chmod +x /root/bootstrap.sh",
+      "/root/bootstrap.sh",
+    ]
+  }
 }
 
 resource "hcloud_volume" "storage" {

infra/modules/prod/variables.tf

@@ -34,7 +34,7 @@ variable "volume_size" {
 }
 
 variable "allowed_ssh_source_ips" {
-  description = "CIDRs allowed to reach port 22 on prod."
+  description = "CIDRs allowed to reach port 22 on prod. Set by the root module to the vpn server's public IP."
   type        = list(string)
 }
 
@@ -42,3 +42,13 @@ variable "network_ip_range" {
   description = "CIDR of the private network, allowed through the firewall for traffic from dev."
   type        = string
 }
+
+variable "bootstrap_script" {
+  description = "Rendered post-install script, uploaded and executed on the server immediately after creation."
+  type        = string
+}
+
+variable "ssh_private_key_path" {
+  description = "Local path to the private key matching var.ssh_key_id, used to run the bootstrap script over SSH."
+  type        = string
+}

infra/modules/vpn/main.tf

@@ -38,4 +38,23 @@ resource "hcloud_server" "this" {
   location     = var.location
   ssh_keys     = [var.ssh_key_id]
   firewall_ids = [hcloud_firewall.this.id]
+
+  connection {
+    type        = "ssh"
+    host        = self.ipv4_address
+    user        = "root"
+    private_key = file(var.ssh_private_key_path)
+  }
+
+  provisioner "file" {
+    content     = var.bootstrap_script
+    destination = "/root/bootstrap.sh"
+  }
+
+  provisioner "remote-exec" {
+    inline = [
+      "chmod +x /root/bootstrap.sh",
+      "/root/bootstrap.sh",
+    ]
+  }
 }

infra/modules/vpn/variables.tf

@@ -22,3 +22,13 @@ variable "allowed_ssh_source_ips" {
   description = "CIDRs allowed to reach port 22 on vpn."
   type        = list(string)
 }
+
+variable "bootstrap_script" {
+  description = "Rendered post-install script, uploaded and executed on the server immediately after creation."
+  type        = string
+}
+
+variable "ssh_private_key_path" {
+  description = "Local path to the private key matching var.ssh_key_id, used to run the bootstrap script over SSH."
+  type        = string
+}

infra/scripts/bootstrap.sh.tftpl

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Post-install bootstrap - uploaded and executed once by OpenTofu immediately
+# after server creation (see modules/<host>/main.tf). Idempotent-ish: safe to
+# re-run by hand, but only ever runs automatically on first create.
+set -euo pipefail
+
+export DEBIAN_FRONTEND=noninteractive
+DEPLOY_USER="${deploy_user}"
+
+apt-get update -y
+apt-get upgrade -y
+
+# --- Docker Engine + Compose plugin ---
+if ! command -v docker >/dev/null 2>&1; then
+  apt-get install -y ca-certificates curl gnupg
+  install -m 0755 -d /etc/apt/keyrings
+  curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
+  chmod a+r /etc/apt/keyrings/docker.asc
+  . /etc/os-release
+  echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu $VERSION_CODENAME stable" \
+    > /etc/apt/sources.list.d/docker.list
+  apt-get update -y
+  apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
+fi
+
+# --- Non-root sudo user, given the same key root was provisioned with ---
+if ! id -u "$DEPLOY_USER" >/dev/null 2>&1; then
+  useradd --create-home --shell /bin/bash "$DEPLOY_USER"
+  usermod -aG sudo,docker "$DEPLOY_USER"
+  mkdir -p "/home/$DEPLOY_USER/.ssh"
+  cp /root/.ssh/authorized_keys "/home/$DEPLOY_USER/.ssh/authorized_keys"
+  chown -R "$DEPLOY_USER:$DEPLOY_USER" "/home/$DEPLOY_USER/.ssh"
+  chmod 700 "/home/$DEPLOY_USER/.ssh"
+  chmod 600 "/home/$DEPLOY_USER/.ssh/authorized_keys"
+  echo "$DEPLOY_USER ALL=(ALL) NOPASSWD:ALL" > "/etc/sudoers.d/90-$DEPLOY_USER"
+  chmod 440 "/etc/sudoers.d/90-$DEPLOY_USER"
+fi
+
+# --- SSH hardening: key-only auth everywhere. Root keeps key-only login as a
+# fallback rather than being fully locked out, in case $DEPLOY_USER setup above
+# ever fails silently on a future image. ---
+sed -i 's/^#\?PermitRootLogin.*/PermitRootLogin prohibit-password/' /etc/ssh/sshd_config
+sed -i 's/^#\?PasswordAuthentication.*/PasswordAuthentication no/' /etc/ssh/sshd_config
+systemctl reload ssh 2>/dev/null || systemctl reload sshd
+
+# --- Unattended security upgrades ---
+apt-get install -y unattended-upgrades
+dpkg-reconfigure -f noninteractive unattended-upgrades
+systemctl enable --now unattended-upgrades

infra/terraform.tfvars.example

@@ -8,11 +8,17 @@
 # (Console > Security > SSH Keys). Required.
 ssh_key_name = "your-key-name"
 
+# Local path to the private key matching ssh_key_name above. OpenTofu uses this
+# once per server to upload and run the post-install bootstrap script
+# (infra/scripts/bootstrap.sh.tftpl) immediately after creation. Required.
+ssh_private_key_path = "~/.ssh/id_ed25519"
+
 # Optional overrides - defaults live in variables.tf
 # location               = "nbg1"
 # dev_server_type        = "cx22"
-# prod_server_type       = "cx32"
+# prod_server_type       = "cx22"
 # vpn_server_type        = "cx22"
-# dev_volume_size        = 50
+# dev_volume_size        = 20
-# prod_volume_size       = 50
+# prod_volume_size       = 20
 # allowed_ssh_source_ips = ["203.0.113.4/32"]
+# deploy_user             = "deploy"

infra/variables.tf

@@ -76,7 +76,18 @@ variable "ssh_key_name" {
 }
 
 variable "allowed_ssh_source_ips" {
-  description = "CIDRs allowed to reach port 22 on every server. Narrow this to your own IP(s) once known."
+  description = "CIDRs allowed to reach port 22 on the vpn server. Narrow this to your own IP(s) once known. dev and prod don't use this - their SSH is restricted to the vpn server's own public IP instead (see infra/main.tf)."
   type        = list(string)
   default     = ["0.0.0.0/0", "::/0"]
 }
+
+variable "ssh_private_key_path" {
+  description = "Local path to the private key matching var.ssh_key_name. Used once per server by OpenTofu to upload and run the post-install bootstrap script over SSH immediately after creation (see infra/scripts/bootstrap.sh.tftpl)."
+  type        = string
+}
+
+variable "deploy_user" {
+  description = "Non-root sudo user created on every server by the bootstrap script, with the same SSH key as root."
+  type        = string
+  default     = "deploy"
+}