amazon-image.nix

# Configuration for Amazon EC2 instances. (Note that this file is a
# misnomer - it should be "amazon-config.nix" or so, not
# "amazon-image.nix", since it's used not only to build images but
# also to reconfigure instances. However, we can't rename it because
# existing "configuration.nix" files on EC2 instances refer to it.)

{ config, lib, pkgs, ... }:

let
  inherit (lib) mkDefault mkIf;
  cfg = config.ec2;
in

{
  imports = [
    ../profiles/headless.nix
    # Note: While we do use the headless profile, we also explicitly
    # turn on the serial console on ttyS0 below. This is because
    # AWS does support accessing the serial console:
    # https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configure-access-to-serial-console.html
    ./ec2-data.nix
    ./amazon-init.nix
  ];

  config = {

    assertions = [ ];

    boot.growPartition = true;

    fileSystems."/" = mkIf (!cfg.zfs.enable) {
      device = "/dev/disk/by-label/nixos";
      fsType = "ext4";
      autoResize = true;
    };

    fileSystems."/boot" = mkIf (cfg.efi || cfg.zfs.enable) {
      # The ZFS image uses a partition labeled ESP whether or not we're
      # booting with EFI.
      device = "/dev/disk/by-label/ESP";
      fsType = "vfat";
    };

    services.zfs.expandOnBoot = mkIf cfg.zfs.enable "all";

    boot.zfs.devNodes = mkIf cfg.zfs.enable "/dev/";

    boot.extraModulePackages = [
      config.boot.kernelPackages.ena
    ];
    boot.initrd.kernelModules = [ "xen-blkfront" ];
    boot.initrd.availableKernelModules = [ "nvme" ];
    boot.kernelParams = [ "console=ttyS0,115200n8" "random.trust_cpu=on" ];

    # Prevent the nouveau kernel module from being loaded, as it
    # interferes with the nvidia/nvidia-uvm modules needed for CUDA.
    # Also blacklist xen_fbfront to prevent a 30 second delay during
    # boot.
    boot.blacklistedKernelModules = [ "nouveau" "xen_fbfront" ];

    boot.loader.grub.device = if cfg.efi then "nodev" else "/dev/xvda";
    boot.loader.grub.efiSupport = cfg.efi;
    boot.loader.grub.efiInstallAsRemovable = cfg.efi;
    boot.loader.timeout = 1;
    boot.loader.grub.extraConfig = ''
      serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
      terminal_output console serial
      terminal_input console serial
    '';

    systemd.services.fetch-ec2-metadata = {
      wantedBy = [ "multi-user.target" ];
      wants = [ "network-online.target" ];
      after = ["network-online.target"];
      path = [ pkgs.curl ];
      script = builtins.readFile ./ec2-metadata-fetcher.sh;
      serviceConfig.Type = "oneshot";
      serviceConfig.StandardOutput = "journal+console";
    };

    # Amazon-issued AMIs include the SSM Agent by default, so we do the same.
    # https://docs.aws.amazon.com/systems-manager/latest/userguide/ami-preinstalled-agent.html
    services.amazon-ssm-agent.enable = true;

    # Allow root logins only using the SSH key that the user specified
    # at instance creation time.
    services.openssh.enable = true;
    services.openssh.settings.PermitRootLogin = "prohibit-password";

    # Enable the serial console on ttyS0
    systemd.services."serial-getty@ttyS0".enable = true;

    # Creates symlinks for block device names.
    services.udev.packages = [ pkgs.amazon-ec2-utils ];

    # Force getting the hostname from EC2.
    networking.hostName = mkDefault "";

    # Always include cryptsetup so that Charon can use it.
    environment.systemPackages = [ pkgs.cryptsetup ];

    # EC2 has its own NTP server provided by the hypervisor
    networking.timeServers = [ "169.254.169.123" ];

    # udisks has become too bloated to have in a headless system
    # (e.g. it depends on GTK).
    services.udisks2.enable = false;
  };
  meta.maintainers = with lib.maintainers; [ arianvp ];
}