feat: scaffold netcup vps host (disko/vda, static net, tailscale, caddy)

- new nixosConfigurations.vps: UEFI systemd-boot, disko on /dev/vda
- static IPv4 159.195.64.117/22 gw .1 (+ IPv6), eth0 pinned, public DNS
- tailscale via headscale + sops authkey (secrets/vps.yaml, own host key)
- caddy public reverse proxy: audiobookshelf.mgaction.town -> jupiter tailnet:8000
- shared common.nix (user/ssh/nix) ; .sops.yaml per-host rules

.sops.yaml

@@ -8,12 +8,16 @@
 keys:
   # admin key — for editing secrets on the laptop (~/.config/sops/age/keys.txt)
   - &admin age1cekcqyf7073fsytcjxaa9dr9zwkmn4vjg36rv2tgxdglzfv4jvxqvcj6z2
-  # jupiter host key — derived from its pre-generated SSH host key with
+  # per-host keys — derived from each box's pre-generated SSH host key
-  # ssh-to-age. The host decrypts at runtime using /etc/ssh/ssh_host_ed25519_key.
+  # (ssh-to-age). The host decrypts at runtime using /etc/ssh/ssh_host_ed25519_key.
   - &jupiter age1zak7glavmg4026p2389fyqe769vqm4jrryknuqckgqq4merz5f7q44rkkt
+  - &vps age1hp72xyx2cnd05937e4eww95g5kdtn0wsf9j2nypw330pa69gfdxqn0lpkp
+# Each host's secrets go to admin (edit) + that host only. Order matters:
+# the first matching rule wins, so keep these specific paths.
 creation_rules:
-  - path_regex: secrets/.*\.yaml$
+  - path_regex: secrets/jupiter\.yaml$
     key_groups:
-      - age:
+      - age: [ *admin, *jupiter ]
-          - *admin
+  - path_regex: secrets/vps\.yaml$
-          - *jupiter
+    key_groups:
+      - age: [ *admin, *vps ]

common.nix

@@ -0,0 +1,41 @@
+{ pkgs, ... }:
+
+# Shared base for all hosts: user, SSH hardening, nix settings, packages.
+# (jupiter still carries its own copy in services.nix; vps uses this.)
+{
+  # ---- User ----
+  users.users.darman = {
+    isNormalUser = true;
+    description = "darman";
+    extraGroups = [ "wheel" "networkmanager" ];
+    openssh.authorizedKeys.keys = [
+      "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGZpkPVhzi1zG5JI9hWyUgdyvNIQbp4ts4jw3idpMhhN erik@laptop"
+    ];
+  };
+  security.sudo.wheelNeedsPassword = false;
+
+  # ---- SSH (key-only) ----
+  services.openssh = {
+    enable = true;
+    settings = {
+      PasswordAuthentication = false;
+      PermitRootLogin = "no";
+    };
+  };
+
+  # ---- Nix ----
+  nix.settings = {
+    experimental-features = [ "nix-command" "flakes" ];
+    # trust wheel so `nixos-rebuild --target-host darman@…` can push closures.
+    trusted-users = [ "root" "@wheel" ];
+  };
+  nix.gc = {
+    automatic = true;
+    dates = "weekly";
+    options = "--delete-older-than 30d";
+  };
+
+  environment.systemPackages = with pkgs; [ vim git htop tmux curl ];
+
+  i18n.defaultLocale = "en_US.UTF-8";
+}

flake.nix

@@ -35,6 +35,17 @@
           ];
         };
 
+        # netcup VPS — public reverse proxy + tailnet node.
+        vps = nixpkgs.lib.nixosSystem {
+          inherit system;
+          specialArgs = { inherit inputs; };
+          modules = [
+            disko.nixosModules.disko
+            sops-nix.nixosModules.sops
+            ./vps/configuration.nix
+          ];
+        };
+
         # VirtualBox test image. Build the OVA with:
         #   nix build .#nixosConfigurations.jupiter-vbox.config.system.build.virtualBoxOVA
         # NOTE: no disko here — the virtualbox-image module supplies the disk.

secrets/vps.yaml

@@ -0,0 +1,25 @@
+tailscale_authkey: ENC[AES256_GCM,data:K9An79w/7ZHl3Pb+TYgH1fzFqEsuBjgMqt4O9lS9csY=,iv:I3SWgDQDiWV/ItUs3biU+EG6nzy446Rd2Cf74fJVpVM=,tag:kn3PXvGkcheKF+26jLK3MQ==,type:str]
+sops:
+    age:
+        - enc: |
+            -----BEGIN AGE ENCRYPTED FILE-----
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBZNVRnY1djOFFpQjEzYzdi
+            ZHhjZWliL2xlK2t6MncxSnk3ZW8ybHFNZ0hNCk0wWHdBajlMQWtjU21QQkxSV1M0
+            bzJhbFBSSmdPU2VTV1NyQmhmUnlJUUEKLS0tIHFTTGlIam9MdllGamc2ZVZIaEFL
+            ZkE4cDk0aTdEMGtxVGM3U2JCMFppalEKnyyQCErY7e5pIFoYS6yYq5puqXAUgClJ
+            U9VkM7G1MZV+Z91XTKs63fd2QyV8ITTK82BMpwH39UzdbbU+mqFvqw==
+            -----END AGE ENCRYPTED FILE-----
+          recipient: age1cekcqyf7073fsytcjxaa9dr9zwkmn4vjg36rv2tgxdglzfv4jvxqvcj6z2
+        - enc: |
+            -----BEGIN AGE ENCRYPTED FILE-----
+            YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBXZER4Q1NFSVJNUFpMS2JQ
+            dVZseHFzc2lWOXVJQmdIZ2xHeWVDMEYyTFJjCkdKckNQNTZ4Zm9hRCtMc2lMZmFF
+            TTh3cVBMVWJGRGY3Z2ErWlBlQUZhL0EKLS0tIGxGZDIzZEhsSFQ5SmNZblk5eHpy
+            ZWpPU1RNZHNIRUhJMXE0dFFtcTRzUmsKnKzMUXY8MKG2Ilgzg1IIr7hvXuvLvzCH
+            EaWB6C+J7/jG3dXfVTfKlubE7x62XDkWMa8OYMFELke/7GU6XXmHWg==
+            -----END AGE ENCRYPTED FILE-----
+          recipient: age1hp72xyx2cnd05937e4eww95g5kdtn0wsf9j2nypw330pa69gfdxqn0lpkp
+    lastmodified: "2026-07-12T22:59:51Z"
+    mac: ENC[AES256_GCM,data:yS13N11tXN2orKAP2ufRNdJbEGkY+bfZiA/7PwSWtgipIlGvnCKbr6yVqMElfNA39Znu+i1sWtk3FxWjRJQ3rM+uRpEdzoseMnYiHkvK0t5hC1ElBxwUdv8v/1RV5/halTV+5G8/lAd48ejgtnLLCpSbw6nPKrDoxb8/Ma5oaj0=,iv:MejfOs5F7eAmwZPsrLUF+6KPxWgACKKbnn5skCisuBo=,tag:X4BI6zDQgqXnnmCVOl25/A==,type:str]
+    unencrypted_suffix: _unencrypted
+    version: 3.13.1

vps/configuration.nix

@@ -0,0 +1,64 @@
+{ config, pkgs, lib, ... }:
+
+# netcup VPS (UEFI, /dev/vda). Public reverse proxy + tailnet node.
+{
+  imports = [
+    ./hardware-configuration.nix
+    ./disk-config.nix          # disko: vda partitions + filesystems
+    ./secrets.nix              # sops-nix: tailscale authkey
+    ../common.nix              # shared user / ssh / nix settings
+  ];
+
+  # ---- Boot (UEFI) ----
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+  # Root is on the virtio disk — pin these so stage-1 mounts it regardless of
+  # what nixos-generate-config detects in the installer.
+  boot.initrd.availableKernelModules = [ "virtio_pci" "virtio_blk" "virtio_scsi" ];
+
+  networking.hostName = "vps";
+
+  # ---- Static networking (netcup) ----
+  # No LAN fallback: get this right or the box is unreachable (use netcup's
+  # VNC console / rescue system to fix). Values captured from the running VPS.
+  networking.useDHCP = false;
+  networking.usePredictableInterfaceNames = false;   # keep the NIC named eth0
+  networking.interfaces.eth0 = {
+    ipv4.addresses = [ { address = "159.195.64.117"; prefixLength = 22; } ];
+    ipv6.addresses = [ { address = "2a0a:4cc0:c2:19e1:44b4:8dff:fe4d:c7d7"; prefixLength = 64; } ];
+  };
+  networking.defaultGateway = { address = "159.195.64.1"; interface = "eth0"; };
+  # netcup IPv6 gateway is conventionally fe80::1 — VERIFY with `ip -6 route`
+  # on the running VPS; wrong v6 gw won't break v4 reachability.
+  networking.defaultGateway6 = { address = "fe80::1"; interface = "eth0"; };
+  # Public resolvers for early boot; tailscale MagicDNS overrides once up.
+  networking.nameservers = [ "9.9.9.9" "1.1.1.1" "2620:fe::fe" ];
+
+  networking.firewall = {
+    enable = true;
+    allowedTCPPorts = [ 22 80 443 ];
+    trustedInterfaces = [ "tailscale0" ];   # reach admin services over the tailnet
+  };
+
+  # ---- Tailscale (via headscale) ----
+  services.tailscale = {
+    enable = true;
+    authKeyFile = config.sops.secrets.tailscale_authkey.path;
+    extraUpFlags = [ "--login-server=https://vpn.mgaction.town" ];
+  };
+
+  # ---- Public reverse proxy ----
+  # Caddy gets automatic public HTTPS (Let's Encrypt) for real domains.
+  # Proxies to jupiter's audiobookshelf over the tailnet (MagicDNS name).
+  # Add one block per public service. Needs a public A record -> this VPS IP
+  # and ports 80/443 open (they are, above).
+  services.caddy = {
+    enable = true;
+    virtualHosts."audiobookshelf.mgaction.town".extraConfig = ''
+      reverse_proxy http://jupiter.hosts.mgaction.town:8000
+    '';
+    # TODO: port your other VPS services' vhosts here before deploying.
+  };
+
+  system.stateVersion = "26.05";   # set at install time; do NOT bump on upgrades
+}

vps/disk-config.nix

@@ -0,0 +1,37 @@
+{ ... }:
+
+# Declarative disk layout (disko) for the netcup VPS.
+# UEFI: GPT with an ESP + ext4 root on the single virtio disk.
+#
+# ⚠️  /dev/vda is WIPED on install — this destroys everything currently on the
+#     VPS (docker containers, data, existing caddy config). Back up / port your
+#     services into NixOS BEFORE running nixos-anywhere.
+{
+  disko.devices.disk.vps = {
+    type = "disk";
+    device = "/dev/vda";        # netcup virtio disk (256G)
+    content = {
+      type = "gpt";
+      partitions = {
+        ESP = {
+          size = "512M";
+          type = "EF00";
+          content = {
+            type = "filesystem";
+            format = "vfat";
+            mountpoint = "/boot";
+            mountOptions = [ "umask=0077" ];
+          };
+        };
+        root = {
+          size = "100%";
+          content = {
+            type = "filesystem";
+            format = "ext4";
+            mountpoint = "/";
+          };
+        };
+      };
+    };
+  };
+}

vps/hardware-configuration.nix

@@ -0,0 +1,23 @@
+# PLACEHOLDER — replace on install.
+#
+# disko (disk-config.nix) owns the filesystems, so this file only carries
+# kernel modules + platform. nixos-anywhere regenerates it via:
+#   nixos-generate-config --no-filesystems
+# Keep the imports/kernel-module lines; the virtio modules are pinned in
+# configuration.nix so root mounts even if the generator misses them.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [ (modulesPath + "/profiles/qemu-guest.nix") ];
+
+  boot.initrd.availableKernelModules = [ "ahci" "xhci_pci" "virtio_pci" "virtio_blk" "sr_mod" ];
+  boot.initrd.kernelModules = [ ];
+  boot.kernelModules = [ ];
+  boot.extraModulePackages = [ ];
+
+  # NO fileSystems here — disko defines "/" and "/boot".
+
+  swapDevices = [ ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}

vps/secrets.nix

@@ -0,0 +1,12 @@
+{ config, ... }:
+
+# sops-nix wiring for the VPS. Encrypted values live in ../secrets/vps.yaml,
+# decrypted with the VPS's own SSH host key (recipient in ../.sops.yaml).
+# The host key is pre-generated on the laptop and shipped at install
+# (nixos-anywhere --extra-files -> /etc/ssh/ssh_host_ed25519_key).
+{
+  sops.defaultSopsFile = ../secrets/vps.yaml;
+  sops.age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
+
+  sops.secrets.tailscale_authkey = { };
+}