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76b614be39
It is surprising that software which was installed by the user at AMI generation time isn't available to a script run over user data by default. When authoring user data to execute at startup, users will now have more predictable access to baked-in software instead of an extremely bare-minimum set currently there.
94 lines
2.8 KiB
Nix
94 lines
2.8 KiB
Nix
{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.virtualisation.amazon-init;
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script = ''
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#!${pkgs.runtimeShell} -eu
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echo "attempting to fetch configuration from EC2 user data..."
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export HOME=/root
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export PATH=${pkgs.lib.makeBinPath [ config.nix.package config.systemd.package pkgs.gnugrep pkgs.git pkgs.gnutar pkgs.gzip pkgs.gnused pkgs.xz config.system.build.nixos-rebuild]}:$PATH
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export NIX_PATH=nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixos:nixos-config=/etc/nixos/configuration.nix:/nix/var/nix/profiles/per-user/root/channels
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userData=/etc/ec2-metadata/user-data
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# Check if user-data looks like a shell script and execute it with the
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# runtime shell if it does. Otherwise treat it as a nixos configuration
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# expression
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if IFS= LC_ALL=C read -rN2 shebang < $userData && [ "$shebang" = '#!' ]; then
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# NB: we cannot chmod the $userData file, this is why we execute it via
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# `pkgs.runtimeShell`. This means we have only limited support for shell
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# scripts compatible with the `pkgs.runtimeShell`.
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exec ${pkgs.runtimeShell} $userData
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fi
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if [ -s "$userData" ]; then
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# If the user-data looks like it could be a nix expression,
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# copy it over. Also, look for a magic three-hash comment and set
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# that as the channel.
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if sed '/^\(#\|SSH_HOST_.*\)/d' < "$userData" | grep -q '\S'; then
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channels="$(grep '^###' "$userData" | sed 's|###\s*||')"
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while IFS= read -r channel; do
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echo "writing channel: $channel"
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done < <(printf "%s\n" "$channels")
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if [[ -n "$channels" ]]; then
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printf "%s" "$channels" > /root/.nix-channels
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nix-channel --update
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fi
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echo "setting configuration from EC2 user data"
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cp "$userData" /etc/nixos/configuration.nix
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else
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echo "user data does not appear to be a Nix expression; ignoring"
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exit
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fi
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else
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echo "no user data is available"
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exit
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fi
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nixos-rebuild switch
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'';
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in {
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options.virtualisation.amazon-init = {
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enable = mkOption {
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default = true;
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type = types.bool;
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description = ''
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Enable or disable the amazon-init service.
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'';
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};
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};
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config = mkIf cfg.enable {
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systemd.services.amazon-init = {
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inherit script;
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description = "Reconfigure the system from EC2 userdata on startup";
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wantedBy = [ "multi-user.target" ];
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after = [ "multi-user.target" ];
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requires = [ "network-online.target" ];
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path = [
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"/run/wrappers"
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"/run/current-system/sw"
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];
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restartIfChanged = false;
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unitConfig.X-StopOnRemoval = false;
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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};
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};
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};
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meta.maintainers = with maintainers; [ arianvp ];
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}
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