# 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, ... }: with lib; let cfg = config.ec2; metadataFetcher = import ./ec2-metadata-fetcher.nix { inherit (pkgs) curl; targetRoot = "$targetRoot/"; wgetExtraOptions = "-q"; }; 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 = [ { assertion = cfg.hvm; message = "Paravirtualized EC2 instances are no longer supported."; } { assertion = cfg.efi -> cfg.hvm; message = "EC2 instances using EFI must be HVM instances."; } ]; boot.growPartition = cfg.hvm; 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" "xen-netfront" ]; boot.initrd.availableKernelModules = [ "ixgbevf" "ena" "nvme" ]; boot.kernelParams = mkIf cfg.hvm [ "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" ]; # Generate a GRUB menu. Amazon's pv-grub uses this to boot our kernel/initrd. boot.loader.grub.version = if cfg.hvm then 2 else 1; boot.loader.grub.device = if (cfg.hvm && !cfg.efi) then "/dev/xvda" else "nodev"; boot.loader.grub.extraPerEntryConfig = mkIf (!cfg.hvm) "root (hd0)"; 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 ''; boot.initrd.network.enable = true; # Mount all formatted ephemeral disks and activate all swap devices. # We cannot do this with the ‘fileSystems’ and ‘swapDevices’ options # because the set of devices is dependent on the instance type # (e.g. "m1.small" has one ephemeral filesystem and one swap device, # while "m1.large" has two ephemeral filesystems and no swap # devices). Also, put /tmp and /var on /disk0, since it has a lot # more space than the root device. Similarly, "move" /nix to /disk0 # by layering a unionfs-fuse mount on top of it so we have a lot more space for # Nix operations. boot.initrd.postMountCommands = '' ${metadataFetcher} diskNr=0 diskForUnionfs= for device in /dev/xvd[abcde]*; do if [ "$device" = /dev/xvda -o "$device" = /dev/xvda1 ]; then continue; fi fsType=$(blkid -o value -s TYPE "$device" || true) if [ "$fsType" = swap ]; then echo "activating swap device $device..." swapon "$device" || true elif [ "$fsType" = ext3 ]; then mp="/disk$diskNr" diskNr=$((diskNr + 1)) if mountFS "$device" "$mp" "" ext3; then if [ -z "$diskForUnionfs" ]; then diskForUnionfs="$mp"; fi fi else echo "skipping unknown device type $device" fi done if [ -n "$diskForUnionfs" ]; then mkdir -m 755 -p $targetRoot/$diskForUnionfs/root mkdir -m 1777 -p $targetRoot/$diskForUnionfs/root/tmp $targetRoot/tmp mount --bind $targetRoot/$diskForUnionfs/root/tmp $targetRoot/tmp if [ "$(cat "$metaDir/ami-manifest-path")" != "(unknown)" ]; then mkdir -m 755 -p $targetRoot/$diskForUnionfs/root/var $targetRoot/var mount --bind $targetRoot/$diskForUnionfs/root/var $targetRoot/var mkdir -p /unionfs-chroot/ro-nix mount --rbind $targetRoot/nix /unionfs-chroot/ro-nix mkdir -m 755 -p $targetRoot/$diskForUnionfs/root/nix mkdir -p /unionfs-chroot/rw-nix mount --rbind $targetRoot/$diskForUnionfs/root/nix /unionfs-chroot/rw-nix unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-nix=RW:/ro-nix=RO $targetRoot/nix fi fi ''; boot.initrd.extraUtilsCommands = '' # We need swapon in the initrd. copy_bin_and_libs ${pkgs.util-linux}/sbin/swapon ''; # Allow root logins only using the SSH key that the user specified # at instance creation time. services.openssh.enable = true; services.openssh.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.ec2-utils ]; # Force getting the hostname from EC2. networking.hostName = mkDefault ""; # Always include cryptsetup so that Charon can use it. environment.systemPackages = [ pkgs.cryptsetup ]; boot.initrd.supportedFilesystems = [ "unionfs-fuse" ]; # 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; }; }