google-compute-image module: use google services

This adds a few google-specific services to setup the machine.

Accounts are now dynamically created using the google-accounts-daemon,
which allows to click on the "SSH" button in the console and have it
working.

The NixOS image now supports the userdata startup and shutdown scripts.

Misc:
* add all the google services from https://github.com/GoogleCloudPlatform/compute-image-packages/tree/master/google_compute_engine_init/systemd
* add udev rules for disk labels
* synched sysctl rules with https://github.com/GoogleCloudPlatform/compute-image-packages/blob/master/google_config/sysctl/11-gce-network-security.conf

nixos/modules/virtualisation/google-compute-image.nix

···
 with lib;
 let
   diskSize = 1024; # MB
+  gce = pkgs.google-compute-engine;
 in
 {
   imports = [ ../profiles/headless.nix ../profiles/qemu-guest.nix ./grow-partition.nix ];
-
-  # https://cloud.google.com/compute/docs/tutorials/building-images
-  networking.firewall.enable = mkDefault false;
 
   system.build.googleComputeImage = import ../../lib/make-disk-image.nix {
     name = "google-compute-image";
···
   services.openssh.permitRootLogin = "prohibit-password";
   services.openssh.passwordAuthentication = mkDefault false;
 
+  # Use GCE udev rules for dynamic disk volumes
+  services.udev.packages = [ gce ];
+
   # Force getting the hostname from Google Compute.
   networking.hostName = mkDefault "";
 
   # Always include cryptsetup so that NixOps can use it.
   environment.systemPackages = [ pkgs.cryptsetup ];
 
+  # Rely on GCP's firewall instead
+  networking.firewall.enable = mkDefault false;
+
   # Configure default metadata hostnames
   networking.extraHosts = ''
     169.254.169.254 metadata.google.internal metadata
···
 
   networking.usePredictableInterfaceNames = false;
 
+  # allow the google-accounts-daemon to manage users
+  users.mutableUsers = true;
+  # and allow users to sudo without password
+  security.sudo.enable = true;
+  security.sudo.extraConfig = ''
+  %google-sudoers ALL=(ALL:ALL) NOPASSWD:ALL
+  '';
+
+  # NOTE: google-accounts tries to write to /etc/sudoers.d but the folder doesn't exist
+  # FIXME: not such file or directory on dynamic SSH provisioning
+  systemd.services.google-accounts-daemon = {
+    description = "Google Compute Engine Accounts Daemon";
+    # This daemon creates dynamic users
+    enable = config.users.mutableUsers;
+    after = [
+      "network.target"
+      "google-instance-setup.service"
+      "google-network-setup.service"
+    ];
+    wantedBy = [ "multi-user.target" ];
+    requires = ["network.target"];
+    path = with pkgs; [ shadow ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${gce}/bin/google_accounts_daemon --debug";
+    };
+  };
+
+  systemd.services.google-clock-skew-daemon = {
+    description = "Google Compute Engine Clock Skew Daemon";
+    after = [
+      "network.target"
+      "google-instance-setup.service"
+      "google-network-setup.service"
+    ];
+    requires = [ "network.target" ];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${gce}/bin/google_clock_skew_daemon --debug";
+    };
+  };
+
+  systemd.services.google-instance-setup = {
+    description = "Google Compute Engine Instance Setup";
+    after = ["fs.target" "network-online.target" "network.target" "rsyslog.service"];
+    before = ["sshd.service"];
+    wants = ["local-fs.target" "network-online.target" "network.target"];
+    wantedBy = [ "sshd.service" "multi-user.target" ];
+    path = with pkgs; [ ethtool ];
+    serviceConfig = {
+      ExecStart = "${gce}/bin/google_instance_setup --debug";
+      Type = "oneshot";
+    };
+  };
+
+  systemd.services.google-ip-forwarding-daemon = {
+    description = "Google Compute Engine IP Forwarding Daemon";
+    after = ["network.target" "google-instance-setup.service" "google-network-setup.service"];
+    requires = ["network.target"];
+    wantedBy = [ "multi-user.target" ];
+    path = with pkgs; [ iproute ];
+    serviceConfig = {
+      Type = "simple";
+      ExecStart = "${gce}/bin/google_ip_forwarding_daemon --debug";
+    };
+  };
+
+  systemd.services.google-shutdown-scripts = {
+    description = "Google Compute Engine Shutdown Scripts";
+    after = [
+      "local-fs.target"
+      "network-online.target"
+      "network.target"
+      "rsyslog.service"
+      "google-instance-setup.service"
+      "google-network-setup.service"
+    ];
+    wants = [ "local-fs.target" "network-online.target" "network.target"];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      ExecStart = "${pkgs.coreutils}/bin/true";
+      ExecStop = "${gce}/bin/google_metadata_script_runner --debug --script-type shutdown";
+      Type = "oneshot";
+      RemainAfterExit = true;
+      TimeoutStopSec = 0;
+    };
+  };
+
+  systemd.services.google-network-setup = {
+    description = "Google Compute Engine Network Setup";
+    after = [
+      "local-fs.target"
+      "network-online.target"
+      "network.target"
+      "rsyslog.service"
+    ];
+    wants = [ "local-fs.target" "network-online.target" "network.target"];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      ExecStart = "${gce}/bin/google_network_setup --debug";
+      KillMode = "process";
+      Type = "oneshot";
+    };
+  };
+
+  systemd.services.google-startup-scripts = {
+    description = "Google Compute Engine Startup Scripts";
+    after = [
+      "local-fs.target"
+      "network-online.target"
+      "network.target"
+      "rsyslog.service"
+      "google-instance-setup.service"
+      "google-network-setup.service"
+    ];
+    wants = [ "local-fs.target" "network-online.target" "network.target"];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      ExecStart = "${gce}/bin/google_metadata_script_runner --debug --script-type startup";
+      KillMode = "process";
+      Type = "oneshot";
+    };
+  };
+
+  # TODO: remove this
   systemd.services.fetch-ssh-keys =
     { description = "Fetch host keys and authorized_keys for root user";
 
···
       serviceConfig.StandardOutput = "journal+console";
     };
 
-  # Setings taken from https://cloud.google.com/compute/docs/tutorials/building-images#providedkernel
+  # Settings taken from https://github.com/GoogleCloudPlatform/compute-image-packages/blob/master/google_config/sysctl/11-gce-network-security.conf
   boot.kernel.sysctl = {
-    # enables syn flood protection
+    # Turn on SYN-flood protections.  Starting with 2.6.26, there is no loss
+    # of TCP functionality/features under normal conditions.  When flood
+    # protections kick in under high unanswered-SYN load, the system
+    # should remain more stable, with a trade off of some loss of TCP
+    # functionality/features (e.g. TCP Window scaling).
     "net.ipv4.tcp_syncookies" = mkDefault "1";
 
     # ignores source-routed packets
···
 
     # randomizes addresses of mmap base, heap, stack and VDSO page
     "kernel.randomize_va_space" = mkDefault "2";
+
+    # Reboot the machine soon after a kernel panic.
+    "kernel.panic" = mkDefault "10";
+
+    ## Not part of the original config
 
     # provides protection from ToCToU races
     "fs.protected_hardlinks" = mkDefault "1";