Deploy & rollback¶

Every change starts in the repository. Machines are never fixed by editing config directly on a host.

Validate before opening a PR¶

GitHub Actions CI is the authoritative build check. Local validation is still useful before opening a PR:

nix flake check --no-build
nix flake show --all-systems

Deploy¶

The normal deployment path is GitHub Actions:

1. Open a PR.
2. Wait for CI to build every host.
3. Merge once the checks are green.
4. Let CD switch yggdrasil, midgard, and alfheim.

See CI/CD pipeline for the workflow details.

Explicit manual path¶

just test and just switch are break-glass/bootstrap commands. Run them only when an operator explicitly asks for a local activation. Building and activation still happen remotely on the target host.

just test <host>     # activate without making it the boot default
just switch <host>   # activate and set as boot default

Hosts: yggdrasil, midgard, alfheim.

Internally this runs:

nixos-rebuild <test|switch>
  --no-reexec
  --flake .#<host>
  --build-host <host>
  --target-host <host>
  --sudo

Rollback¶

Roll back to the previous generation on the host:

sudo nixos-rebuild switch --rollback

If the system no longer boots, pick the previous generation from the systemd-boot menu.

Caveats¶

• Never edit flake.lock by hand; use nix flake update.
• system.stateVersion records initial-install defaults; do not bump it unless release notes explicitly say to.
• Deploys touch live hosts: use CI/CD for normal changes, and run local just test / just switch only on explicit request.