The homelab hosts accept root SSH with long-lived file keys, run several
exposed services with almost no systemd sandboxing, and keep no audit trail of
privileged actions. Close those three gaps, weighing each measure against its
cost instead of adopting a policy wholesale.
SSH
- Turn off KbdInteractiveAuthentication: nixpkgs defaults it to true and PAM
then still accepts the Unix password despite PasswordAuthentication = false.
- authorizedKeysInHomedir = false: only keys declared in Nix take effect;
youko keeps Gitea's forced-command file through `Match User gitea`.
- Pin aquamarine's passphrase-free remote-builder keys to
`restrict,command="nix-daemon --stdio --store daemon"`, so builds run in the
system daemon instead of an audited root login session.
systemd sandboxing
- Add the mylib.systemdHardening preset and apply it to the exposed, weakly
sandboxed services: caddy 7.8 -> 1.5, vmalert 8.2 -> 1.4, rustfs 6.6 -> 1.4,
whisper-asr 7.7 -> 1.6. An eval test pins the key restrictions.
- Rejected: a global all-keys policy (<=0.2 score gains on services nixpkgs
already sandboxes) and per-service confinement (bind paths to maintain).
auditd on all four hosts, reusing nixpkgs' loader and unit
- Audit login sessions only: a first `-a never,task -F auid=unset` rule keeps
services out of the per-syscall audit path. A compromised service is
therefore unrecorded until it opens a session.
- Record root commands, credential and host-key access, writes to SSH, account,
PAM, Nix-trust and audit configuration, module loads and session denials.
- Rejected: global denial logging, service-UID watches and
--loginuid-immutable (the kernel already records loginuid changes).
Verified on all four hosts after deployment: zero failed units, k3s 6/6 Ready,
and the exposed services healthy.
Assisted-by: Claude Code (claude-opus-5-5)
Add worker-1 (4 vCPU / 16 GiB) on shoryu, and worker-2 (4 vCPU / 16 GiB) plus worker-3 (2 vCPU / 8 GiB) on shushou, as microVMs. They come with a genK3sAgentModule and the per-host/output/home-manager wiring, and are labelled node-role.kubernetes.io/worker=true. The masters keep their control-plane:NoSchedule taint, so workloads land on the workers.
The k3s-test workers never ran (they were stuck waiting for volume
binding) and will be re-added as microVMs, so remove their KubeVirt
configs and everything that only existed for KubeVirt guests:
- hosts/k8s/k3s-test-1-worker-{1,2,3} and their outputs
- lib/genKubeVirtGuestModule.nix and lib/genK3sAgentModule.nix (the
latter was only used by the workers)
- the KubeVirt image upload recipes (upload-vm, upload-idols,
upload-k3s-test) and the kubevirt image package in the idols outputs
- refresh the docs; keep only accurate historical mentions (e.g. the
restic backup path must stay as it is)
The physical hosts no longer need k3s or KubeVirt: aquamarine runs
natively, the k3s-test masters run as microVMs and kana/ruby under
libvirt. So drop the host cluster and split the shared parts out of the
KubeVirt host module:
- lib/genVmHostModule.nix: the host bits the VMs still need (br0 + the
physical NIC as a bridge port, KVM, sysctls, earlyoom, libvirt,
journald, stateVersion)
- the three hosts use it and drop genK3sServerModule; also drop the
longhorn workarounds (openiscsi + the /usr/local/bin tmpfile) and the
virtctl package
- remove lib/genKubeVirtHostModule.nix
lib/genMicrovmGuestModule.nix: qemu guest with a shared read-only store
(virtiofs), persistent /etc, /var and /home volumes, a tap on br0 (its
name derived from the guest IP, as IFNAMSIZ caps it at 15 chars), and a
deterministic MAC. Also keep lib/*.nix tracked.
Ryan Yin
ryan4yin | 二花