clan-lib: Always set a static private key for nixos-anywhere, to make --phases work properly

pkgs/clan-cli/clan_cli/machines/install.py

@@ -58,6 +58,9 @@ def install_command(args: argparse.Namespace) -> None:
         else:
             target_host = machine.target_host().override(host_key_check=host_key_check)
 
+        if args.identity_file:
+            target_host = target_host.override(private_key=args.identity_file)
+
         if machine._class_ == "darwin":
             msg = "Installing macOS machines is not yet supported"
             raise ClanError(msg)

pkgs/clan-cli/clan_lib/dirs/__init__.py

@@ -120,6 +120,12 @@ def user_cache_dir() -> Path:
     return Path("~/.cache").expanduser()
 
 
+def user_nixos_anywhere_dir() -> Path:
+    p = user_config_dir() / "clan" / "nixos-anywhere"
+    p.mkdir(parents=True, exist_ok=True)
+    return p
+
+
 def user_gcroot_dir() -> Path:
     p = user_config_dir() / "clan" / "gcroots"
     p.mkdir(parents=True, exist_ok=True)

pkgs/clan-cli/clan_lib/machines/install.py

@@ -13,6 +13,7 @@ from clan_lib.api import API
 from clan_lib.cmd import Log, RunOpts, run
 from clan_lib.machines.machines import Machine
 from clan_lib.nix import nix_shell
+from clan_lib.ssh.create import create_nixos_anywhere_ssh_key
 from clan_lib.ssh.remote import Remote
 
 log = logging.getLogger(__name__)
@@ -25,6 +26,7 @@ BuildOn = Literal["auto", "local", "remote"]
 class InstallOptions:
     machine: Machine
     kexec: str | None = None
+    anywhere_priv_key: Path | None = None
     debug: bool = False
     no_reboot: bool = False
     phases: str | None = None
@@ -115,8 +117,18 @@ def run_machine_install(opts: InstallOptions, target_host: Remote) -> None:
                 "IdentitiesOnly=yes",
             ]
 
+        # Always set a nixos-anywhere private key to prevent failures when running
+        # 'clan install --phases kexec' followed by 'clan install --phases disko,install,reboot'.
+        # The kexec phase requires an authorized key, and if not specified,
+        # nixos-anywhere defaults to a key in a temporary directory.
+        if opts.anywhere_priv_key is None:
+            key_pair = create_nixos_anywhere_ssh_key()
+            opts.anywhere_priv_key = key_pair.private
+        cmd += ["-i", str(opts.anywhere_priv_key)]
+
+        # If we need a different private key for being able to kexec, we can specify it here.
         if target_host.private_key:
-            cmd += ["-i", str(target_host.private_key)]
+            cmd += ["--ssh-option", f"IdentityFile={target_host.private_key}"]
 
         if opts.build_on:
             cmd += ["--build-on", opts.build_on]

pkgs/clan-cli/clan_lib/ssh/create.py

@@ -0,0 +1,61 @@
+import logging
+from dataclasses import dataclass
+from pathlib import Path
+
+from clan_lib.api import API
+from clan_lib.cmd import Log, RunOpts, run
+from clan_lib.dirs import user_nixos_anywhere_dir
+
+log = logging.getLogger(__name__)
+
+
+@dataclass(frozen=True)
+class SSHKeyPair:
+    private: Path
+    public: Path
+
+
+@API.register
+def create_nixos_anywhere_ssh_key() -> SSHKeyPair:
+    """
+    Create a new SSH key pair for NixOS Anywhere.
+    The keys are stored in ~/.config/clan/nixos-anywhere/keys/id_ed25519 and id_ed25519.pub.
+    """
+    private_key_dir = user_nixos_anywhere_dir()
+
+    key_pair = generate_ssh_key(private_key_dir)
+
+    return key_pair
+
+
+def generate_ssh_key(root_dir: Path) -> SSHKeyPair:
+    """
+    Generate a new SSH key pair at root_dir/keys/id_ed25519 and id_ed25519.pub.
+    If the key already exists, it will not be regenerated.
+    """
+    key_dir = root_dir / "keys"
+    key_dir.mkdir(parents=True, exist_ok=True)
+    key_dir.chmod(0o700)
+    priv_key = key_dir / "id_ed25519"
+
+    keypair = SSHKeyPair(
+        private=priv_key,
+        public=key_dir / "id_ed25519.pub",
+    )
+
+    if priv_key.exists():
+        return keypair
+
+    log.info(f"Generating nixos-anywhere SSH key pair at {priv_key}")
+    cmd = [
+        "ssh-keygen",
+        "-N",
+        "",
+        "-t",
+        "ed25519",
+        "-f",
+        str(priv_key),
+    ]
+    run(cmd, RunOpts(log=Log.BOTH))
+
+    return keypair

pkgs/clan-cli/clan_lib/ssh/create_test.py

@@ -0,0 +1,28 @@
+from pathlib import Path
+
+from clan_lib.ssh.create import create_nixos_anywhere_ssh_key
+
+
+def test_clan_generate_sshkeys(temporary_home: Path) -> None:
+    keypair = create_nixos_anywhere_ssh_key()
+
+    assert keypair.private.exists()
+    assert keypair.public.exists()
+    assert keypair.private.is_file()
+    assert keypair.public.is_file()
+    assert (
+        keypair.private.parent
+        == Path("~/.config/clan/nixos-anywhere/keys").expanduser()
+    )
+    assert (
+        keypair.public.parent == Path("~/.config/clan/nixos-anywhere/keys").expanduser()
+    )
+    assert keypair.private.name == "id_ed25519"
+    assert keypair.public.name == "id_ed25519.pub"
+    assert "PRIVATE KEY" in keypair.private.read_text()
+    assert "ssh-ed25519" in keypair.public.read_text()
+
+    new_keypair = create_nixos_anywhere_ssh_key()
+
+    assert new_keypair.private == keypair.private
+    assert new_keypair.public == keypair.public