machines update: support local build

Now the user can pass `--build-host local`, to select the local machine as a build host, in which case no ssh is used.

This means the admin machine does not necessarily have ssh set up to itself, which was confusing for many users.

Also this makes it easier to re-use a well configured nix remote build setup which is only available on the local machine. Eg if `--build-host local` nix' defaults for remote builds on that machine will be utilized.

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

@@ -13,7 +13,9 @@ from clan_lib.machines.machines import Machine
 from clan_lib.machines.suggestions import validate_machine_names
 from clan_lib.machines.update import run_machine_update
 from clan_lib.nix import nix_config
+from clan_lib.ssh.host import Host
 from clan_lib.ssh.host_key import HostKeyCheck
+from clan_lib.ssh.localhost import LocalHost
 from clan_lib.ssh.remote import Remote
 
 from clan_cli.completions import (
@@ -128,6 +130,19 @@ def update_command(args: argparse.Namespace) -> None:
         host_key_check = args.host_key_check
         with AsyncRuntime() as runtime:
             for machine in machines_to_update:
+                # figure out on which machine to build on
+                build_host: Host | None = None
+                if args.build_host:
+                    if args.build_host == "local":
+                        build_host = LocalHost()
+                    else:
+                        build_host = Remote.from_ssh_uri(
+                            machine_name=machine.name,
+                            address=args.build_host,
+                        ).override(host_key_check=host_key_check)
+                else:
+                    build_host = machine.build_host()
+                # Figure out the target host
                 if args.target_host:
                     target_host = Remote.from_ssh_uri(
                         machine_name=machine.name,
@@ -137,6 +152,7 @@ def update_command(args: argparse.Namespace) -> None:
                     target_host = machine.target_host().override(
                         host_key_check=host_key_check
                     )
+                # run the update
                 runtime.async_run(
                     AsyncOpts(
                         tid=machine.name,
@@ -145,7 +161,7 @@ def update_command(args: argparse.Namespace) -> None:
                     run_machine_update,
                     machine=machine,
                     target_host=target_host,
-                    build_host=machine.build_host(),
+                    build_host=build_host,
                     force_fetch_local=args.fetch_local,
                 )
             runtime.join_all()
@@ -189,7 +205,10 @@ def register_update_parser(parser: argparse.ArgumentParser) -> None:
     parser.add_argument(
         "--build-host",
         type=str,
-        help="Address of the machine to build the flake, in the format of user@host:1234.",
+        help=(
+            "The machine on which to build the machine configuration.\n"
+            "Pass 'local' to build on the local machine, or an ssh address like user@host:1234\n"
+        ),
     )
     parser.add_argument(
         "--fetch-local",

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

@@ -18,7 +18,6 @@ from clan_lib.errors import ClanError
 from clan_lib.machines.machines import Machine
 from clan_lib.nix import nix_command, nix_metadata
 from clan_lib.ssh.host import Host
-from clan_lib.ssh.remote import Remote
 
 log = logging.getLogger(__name__)
 
@@ -133,7 +132,7 @@ def run_machine_update(
         if build_host is None:
             build_host = target_host
         else:
-            stack.enter_context(build_host.host_connection())
+            build_host = stack.enter_context(build_host.host_connection())
 
         # Some operations require root privileges on the target host.
         target_host_root = stack.enter_context(target_host.become_root())