Sergei Poljanski
0b331bc5f1
The first run failed with "home directory /homeless-shelter exists": job containers are unprivileged, Nix cannot sandbox builds in them, and unsandboxed builds trip over each other's leftovers. Evaluate the system in the job instead, which still catches broken options before main, and let nixos-rebuild build on the target host, where the Nix daemon has a proper sandbox. Assisted-by: Claude:fable-5-2
85 lines
3.1 KiB
Markdown
85 lines
3.1 KiB
Markdown
# NixOS
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The whole system of a server, as one flake. `asxpio-services` runs
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NixOS; `asxpio-ops` is still Debian and managed by `../ansible`.
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```
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flake.nix inputs (nixpkgs 26.05, disko, sops-nix), hosts
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modules/base.nix users, SSH, fail2ban, journal cap
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modules/hetzner.nix disk layout and boot for a Hetzner Cloud VM
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hosts/asxpio-services/ network, WireGuard, firewall, containers, CI runner
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hosts/rehearsal.nix overrides for a throwaway test server
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secrets/*.yaml sops-encrypted secrets
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migration/ one-off scripts for the move from Debian
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```
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Containers run under Podman, one systemd unit each:
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`systemctl status podman-minecraft`, `journalctl -u podman-sillytavern`.
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`docker` is an alias for `podman`, and `/run/docker.sock` is Podman's
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Docker-compatible socket, which the CI runner uses to start jobs.
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## Changing something
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Edit, push a branch (CI evaluates the system), merge to `main` (CI
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builds it on the server and switches to it). By hand, over WireGuard:
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```sh
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nixos-rebuild switch --flake .#asxpio-services --target-host root@10.20.0.20
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```
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A deploy restarts only the units whose definition changed. Changing a
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Minecraft container restarts that server; it gets 120 s to save first.
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A bad deploy is undone with `nixos-rebuild switch --rollback` on the
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host, or by picking the previous generation in the boot menu.
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To update all packages: `nix flake update`, commit `flake.lock`.
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## Secrets
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`secrets/asxpio-services.yaml` is encrypted with
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[sops](https://github.com/getsops/sops) for two keys listed in
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`.sops.yaml`: the admin's age key and the server's SSH host key. The
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server decrypts at boot into `/run/secrets`.
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```sh
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sops secrets/asxpio-services.yaml # edit; needs ~/.config/sops/age/keys.txt
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```
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The server's SSH host key is therefore part of its identity. Keep a copy
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outside the server (the `system` archive of a backup contains
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`/etc/ssh`), and hand it to a reinstall with `--extra-files`.
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## Installing or reinstalling a server
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Never delete and recreate a production server: it is billed at an old
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price that a new server would not get. Reinstall in place.
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1. Put the host key where the installer will copy it from:
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```sh
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mkdir -p extra/etc/ssh # then place ssh_host_ed25519_key{,.pub}, mode 600
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```
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2. Install. The running system is replaced; **the disk is wiped**.
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```sh
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nix run github:nix-community/nixos-anywhere -- \
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--flake .#asxpio-services --extra-files extra \
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--ssh-option ProxyJump=root@10.20.0.10 root@10.10.0.20
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```
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The installer has no WireGuard, so it is reached over the private
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network through asxpio-ops.
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3. Restore data with `migration/restore-services.sh`. Containers that
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own data do not start until `/opt/.restored` exists, so nothing
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generates a fresh world where the restore is about to land.
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If a server is ever lost entirely, `terraform apply` creates a bare one
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and the steps above install onto it.
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## Rehearsal
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`.#rehearsal` is the same system for a throwaway server: plain DHCP, SSH
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from anywhere, no WireGuard, dummy secrets. Use it to try an install or
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a risky change before production.
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