diff --git a/aspects/ephemeral.nix b/aspects/ephemeral.nix new file mode 100644 index 0000000..724f931 --- /dev/null +++ b/aspects/ephemeral.nix @@ -0,0 +1,136 @@ +# Ephemeral root aspect - provides automatic btrfs root subvolume rollover +# Exports both a base module with options and a factory function for easy configuration +{ inputs, ... }: +{ + # Base module with options (for external flakes or direct use) + flake.modules.nixos.ephemeral = { lib, config, ... }: + let + cfg = config.ephemeral; + in + { + options.ephemeral = { + enable = lib.mkEnableOption "ephemeral root with automatic rollback"; + + rootDevice = lib.mkOption { + type = lib.types.str; + example = "/dev/mapper/cryptroot"; + description = "Device path for the root btrfs filesystem"; + }; + + rootSubvolume = lib.mkOption { + type = lib.types.str; + default = "@root"; + description = "Name of the root btrfs subvolume"; + }; + + oldRootRetentionDays = lib.mkOption { + type = lib.types.int; + default = 30; + description = "Number of days to keep old root snapshots before deletion"; + }; + }; + + config = lib.mkIf cfg.enable { + boot.initrd.systemd.services.recreate-root = { + description = "Rolling over and creating new filesystem root"; + requires = [ "initrd-root-device.target" ]; + after = [ + "local-fs-pre.target" + "initrd-root-device.target" + ]; + requiredBy = [ "initrd-root-fs.target" ]; + before = [ "sysroot.mount" ]; + unitConfig = { + AssertPathExists = "/etc/initrd-release"; + DefaultDependencies = false; + }; + serviceConfig = { + Type = "oneshot"; + RemainAfterExit = true; + }; + script = '' + set -euo pipefail + + mkdir /btrfs_tmp + if ! mount ${cfg.rootDevice} /btrfs_tmp; then + echo "ERROR: Failed to mount ${cfg.rootDevice}" + exit 1 + fi + + if [[ -e /btrfs_tmp/${cfg.rootSubvolume} ]]; then + mkdir -p /btrfs_tmp/old_roots + timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/${cfg.rootSubvolume})" "+%Y-%m-%-d_%H:%M:%S") + mv /btrfs_tmp/${cfg.rootSubvolume} "/btrfs_tmp/old_roots/$timestamp" + fi + + delete_subvolume_recursively() { + IFS=$'\n' + for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do + delete_subvolume_recursively "/btrfs_tmp/$i" + done + btrfs subvolume delete "$1" + } + + for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +${toString cfg.oldRootRetentionDays}); do + delete_subvolume_recursively "$i" + done + + if ! btrfs subvolume create /btrfs_tmp/${cfg.rootSubvolume}; then + echo "ERROR: Failed to create subvolume ${cfg.rootSubvolume}" + umount /btrfs_tmp + exit 1 + fi + + umount /btrfs_tmp + ''; + }; + }; + }; + + # Factory function that generates configured modules + flake.factory.ephemeral = + { rootDevice + , rootSubvolume ? "@root" + , retentionDays ? 30 + , persistentStoragePath ? "/persistent" + , persistentFiles ? [ + "/etc/machine-id" + "/etc/ssh/ssh_host_ed25519_key" + "/etc/ssh/ssh_host_ed25519_key.pub" + "/etc/ssh/ssh_host_rsa_key" + "/etc/ssh/ssh_host_rsa_key.pub" + ] + , persistentDirectories ? [ + "/etc/NetworkManager/system-connections" + "/etc/nixos" + "/var/lib/bluetooth" + "/var/lib/flatpak" + "/var/lib/lxd" + "/var/lib/nixos" + "/var/lib/systemd/coredump" + "/var/lib/systemd/timers" + "/var/lib/tailscale" + "/var/log" + ] + }: + { ... }: { + imports = [ + inputs.impermanence.nixosModules.impermanence + inputs.self.modules.nixos.ephemeral + ]; + + ephemeral = { + enable = true; + inherit rootDevice rootSubvolume; + oldRootRetentionDays = retentionDays; + }; + + fileSystems."/persistent".neededForBoot = true; + + environment.persistence.main = { + inherit persistentStoragePath; + files = persistentFiles; + directories = persistentDirectories; + }; + }; +}