feat(vpn-ingress): WireGuard remote access on udp/51820 (hostNetwork, declarative peers)

Lets the operator's Android / Linux / Windows / macOS devices dial in from
anywhere and behave like LAN machines: full reach to 192.168.2.0/24 plus
internet egress out the house WAN. Opposite direction to platform/vpn-egress,
which sends pods OUT through PIA; the two share nothing but the word "VPN".

WireGuard because it is the only option with a first-party client on all four
named platforms, and because its handshake MAC is keyed with the responder's
own public key: an unauthenticated packet gets NO reply, so udp/51820 is
indistinguishable from a closed port. That, not "it is encrypted", is what
makes an unfiltered WAN port defensible, and why there is no source allowlist.

hostNetwork: true is REQUIRED, not convenient. A pod-networked server must SNAT
clients to its own pod IP, so every remote client would carry that pod's Cilium
identity -- and a pod-sourced request to the shared Gateway VIP returns 403 from
Envoy for ALL 16 hostnames (measured 2026-10-04), because Cilium's Gateway
preserves the original source identity and enforces the destination's ingress
policy. The obvious build would have shipped a healthy-looking tunnel on which
every cluster web UI was 403 and *.home.keithjackson.dev did not even resolve.
In the host netns traffic is SNATed to the node and arrives as host/remote-node,
exactly like a LAN client. It also sidesteps the unsafe ip_forward sysctl, the
L2-announcement lease lottery, and double encapsulation (hence MTU 1420).
Permitted by restrict-host-namespaces' own carve-out for platform namespaces.
The cost is stated in networkpolicy.yaml rather than papered over: no
NetworkPolicy constrains a hostNetwork pod.

A DaemonSet so the hand-made WAN forward cannot be invalidated by a reschedule;
all three nodes answer the same keys, so failover is a one-line router change.

Peer PUBLIC keys are plaintext in peers.yaml, which makes "who can get into my
house" a reviewable PR diff. The only secret -- the server's private key -- is
an out-of-band Secret: an agent must not mint a long-lived private key, and the
two halves are joined only at pod start into a tmpfs that dies with the pod.

Ships INERT-BUT-HEALTHY with zero peers. THREE off-repo manual steps remain
(kernel module, server key, WAN forward) -- runbooks/vpn-remote-access.md.

Touches clusters/** , so ci/approval-policy.sh will block pending the
operator's /approve-override. Deliberately not posted by me (CLAUDE.md §1).

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

decisions/2026-10-05-vpn-remote-access-wireguard.md

@@ -0,0 +1,208 @@
+---
+date: 2026-10-05
+branch: feat/vpn-remote-access-wireguard
+title: Remote-access VPN — WireGuard on udp/51820, hostNetwork because a pod identity would 403 every Gateway hostname
+---
+
+## What changed
+
+New platform component `platform/vpn-ingress/`: a **WireGuard** remote-access VPN so the operator's
+Android / Linux / Windows / macOS devices can dial in from anywhere on the internet and behave like
+machines on the LAN — full reach to `192.168.2.0/24` plus internet egress out the house WAN.
+
+This is the **opposite direction** to the existing `platform/vpn-egress` (pods *out* through PIA,
+ADR-0015). They share nothing but the word "VPN"; both READMEs now say so, and `README.md`'s layout
+block labels the two.
+
+**Transport: WireGuard, and the security argument is the handshake's failure mode, not "it is
+encrypted".** WireGuard's first handshake message carries a MAC keyed with the responder's own
+public key, so a sender that does not already know it gets **no reply at all** — no error, no reset,
+no banner. From the internet, udp/51820 is indistinguishable from a closed port: nothing to
+brute-force, no version string, no amplification. That is what makes an unfiltered WAN port
+defensible here, and it is why there is deliberately no `loadBalancerSourceRanges`-style allowlist
+(which would also break roaming clients). It also has first-party clients on all four named
+platforms, which OpenVPN (needs a CA + per-device certs + a CRL) and IKEv2 do not.
+
+**`hostNetwork: true`, and this is THE decision — forced by a measured property of this cluster.**
+A pod-networked WireGuard server must SNAT client traffic to its own pod IP (Cilium drops a packet
+whose source is not the endpoint's address), so every remote client would have arrived wearing *that
+pod's* security identity. `decisions/2026-10-04-plex-advertise-plexdirect.md` measured what that
+costs: a request to the shared Gateway VIP **from inside a pod returns `403 Access denied` from
+Envoy for all 16 Gateway hostnames**, because Cilium's Gateway preserves the original source
+identity and enforces the *destination's* ingress policy, and every app admits `reserved:ingress`
+plus named peers — never an arbitrary pod. So the obvious build would have produced a tunnel that
+came up healthy, showed connected peers, routed packets, and 403'd every cluster web UI — and
+`*.home.keithjackson.dev` would not even have resolved, because `apps/wave-0/pihole-dns.yaml`'s
+ingress policy deliberately omits the `cluster` entity. In the host netns there is no pod identity
+to carry: forwarded traffic is SNATed to the node address and arrives as `host`/`remote-node`,
+byte-for-byte what a LAN client looks like. Three further problems vanish with it: `ip_forward` is
+already 1 on these nodes (so no `--allowed-unsafe-sysctls` kubelet change — it is *not* a safe
+sysctl); no LoadBalancer VIP, so no L2-announcement lease lottery and no `externalTrafficPolicy`
+trade-off; and no double encapsulation, which is what makes `MTU = 1420` simply correct.
+
+`hostNetwork` is permitted by `restrict-host-namespaces`' own stated carve-out (it matches
+`app-namespace=true` only, and names Cilium/node-exporter as the precedent); `namespace.yaml` is
+deliberately unlabelled. **The cost is stated, not buried:** a hostNetwork pod has no Cilium
+endpoint, so **no NetworkPolicy constrains this workload**. `networkpolicy.yaml` says that at
+length rather than shipping an `allow world → 51820` rule that would read as the control and
+enforce nothing; the real boundary is WireGuard's peer authentication.
+
+**A DaemonSet, not a Deployment.** The WAN forward names one node address by hand, off-repo (same
+shape as the plex tcp/32400 forward). A floating single replica would silently invalidate it on
+every reschedule; an identical listener on all three nodes makes **failover a one-line router
+change** with no cluster work and no re-issued client profiles. A pinned LoadBalancer VIP was the
+considered alternative and was rejected: it reintroduces the L2 lease, SNAT and an extra node hop
+into the one path whose failure mode is "I am away from home and cannot get in".
+
+**Authorisation is split so that it stays reviewable.** Peer **public** keys live in
+`platform/vpn-ingress/peers.yaml` in **plaintext** — a public key grants nothing by itself, and this
+makes "who can get into my house" a PR diff with `git log` as its audit trail. The only real secret,
+the server's private key, is the `wg-server-key` Secret, **created out of band by the operator**: an
+agent must not mint a long-lived private key (CLAUDE.md §6), and a key that passed through a session
+transcript would have to be treated as compromised. The two halves are joined only at pod start, by
+an init container, into a `medium: Memory` emptyDir — so the assembled config holding the key never
+touches a node's disk and dies with the pod.
+
+**There are no peers yet, and that is the correct initial state**, for the same reason. The VPN ships
+INERT-BUT-HEALTHY: a zero-peer interface listens and refuses every handshake.
+
+Files:
+
+- `platform/vpn-ingress/` (new): `namespace.yaml`, `peers.yaml` (the plaintext peer register),
+  `daemonset.yaml` (hostNetwork listener + config assembly), `networkpolicy.yaml` (namespace
+  baseline, with the honest caveat), `kustomization.yaml`, `README.md` (the design record).
+- `clusters/base/vpn-ingress.yaml` (new): its own **non-gating post-platform** Flux Kustomization
+  (`dependsOn platform-config`, `wait:false`). Non-gating is load-bearing rather than conventional
+  here: the DaemonSet *cannot* start until the operator creates the server key, so in the gating
+  `platform` tier an unfinished manual step would have stalled every apps wave on merge.
+- `clusters/base/kustomization.yaml`: the new tier added.
+- `clusters/base/cluster-vars.yaml`: new `WG_CLIENT_CIDR` (`10.90.0.0/24`), declared next to
+  `LAN_CIDR` because it is the one range that must be collision-checked against every other; the
+  comment enumerates the five it avoids. **No prod override, deliberately** — unlike every VIP, this
+  range is private to the tunnel, so the same value is correct in both environments and a prod patch
+  would imply otherwise. Substitution inventory updated.
+- `infra/ansible/roles/node_baseline/defaults/main.yml`: `wireguard` added to
+  `node_baseline_kernel_modules`. The pod has `NET_ADMIN` but deliberately **not** `SYS_MODULE`, so
+  it cannot autoload the module — it CrashLoops with a clear error rather than quietly degrading to
+  userspace wireguard-go (which would need `/dev/net/tun`, a device a hostPath mount cannot actually
+  grant, as the `/dev/dri` attempt proved).
+- `infra/vpn-ingress/new-peer.sh` (new): enrols a device. Generates the keypair on the operator's
+  machine, writes a 0600 profile **outside** the checkout (it refuses to write into the repo),
+  prints a QR code for phones, and prints only the public `[Peer]` stanza. It also refuses a
+  duplicate address, because two devices on one address does not error anywhere — the server routes
+  to whichever handshook last, so both appear to work intermittently.
+- `runbooks/vpn-remote-access.md` (new) + its `kustomization.yaml` generator entry + `README.md`
+  index line: the three manual steps, the four off-LAN verification checks, revocation, and why no
+  connection alert exists.
+- `README.md`: `vpn-ingress` added to the layout, with the egress/ingress distinction spelled out.
+
+**THREE MANUAL STEPS REMAIN AND THE VPN DOES NOT WORK UNTIL ALL THREE ARE DONE** (all off-repo by
+necessity; `runbooks/vpn-remote-access.md`): run `node_baseline` to load the kernel module, create
+the `wg-server-key` Secret, and forward WAN udp/51820 to one node address on the SOHO router.
+
+**SENSITIVE PATHS — this PR touches `clusters/**` (three files), so `ci/approval-policy.sh` will
+BLOCK it.** It needs the operator's `/approve-override <reason>` posted as a PR **review** of type
+"Comment". I have deliberately not posted it: CLAUDE.md §1 forbids an agent clearing this on its own
+PR, and the agent account holds `owner`, so the prohibition is a rule, not a limit.
+
+## What I verified
+
+Live prod, read-only, 2026-10-05, plus the offline gate.
+
+- **Toolbox gate** (`./infra/devcontainer/dev.sh run bash -c './ci/gate.sh'`): **rc 3**, with
+  `spec-immutability`, `decisions-log`, `lint`, `l0`, `render-golden`, `l1` and `approval-policy` all
+  **pass**. The rc 3 is two environmental skips — `gitea-settings` (no local `SETTINGS_API_TOKEN`)
+  and `conformance` L2/L3 (`CLUSTER_AVAILABLE` unset). **Not green. Reported as rc 3, not as pass.**
+- **`flux-postbuild-substitution` (L0) actually exercised the new wiring, and caught a real defect
+  in it.** On the first run it FAILED, naming `platform/vpn-ingress/daemonset.yaml:118` and
+  attributing it to "Flux Kustomization 'vpn-ingress' (clusters/base/vpn-ingress.yaml, path
+  ./platform/vpn-ingress)". Two things are proven by that message: the new tier's
+  `postBuild.substituteFrom` declaration is correctly detected (so `${WG_CLIENT_CIDR}` will be
+  substituted, not shipped literally), and the check reads comments as well as values — the hazard
+  was a comment that spelled out the forbidden braced form literally while claiming not to use it.
+  Fixed; the check now passes 444/444 with 0 hazards.
+- **The `wireguard` kernel module is available on these nodes by construction**: all three run
+  Debian 13 (trixie) on kernel `7.1.8+deb13-amd64` (measured), and WireGuard has been in-tree since
+  5.6, so it is present in the distro kernel and only needs loading.
+- **`net.ipv4.ip_forward = 1` is already written by `node_baseline`**
+  (`roles/node_baseline/tasks/main.yml`, `/etc/sysctl.d/99-k3s-cilium.conf`), and **no kubelet
+  carries `--allowed-unsafe-sysctls`** (grepped across `roles/k3s_server`, `roles/node_baseline` and
+  `group_vars`: zero hits). That pair is what makes the host netns the only option that does not
+  require a node-restart change.
+- **Cilium's datapath, measured from `cilium-config` rather than from the values file**:
+  `enable-ipv4-masquerade=true`, `enable-bpf-masquerade=true`, `routing-mode=tunnel`,
+  `tunnel-protocol=vxlan`, `ipv4-native-routing-cidr` EMPTY, Cilium `v1.20.1`. The vxlan underlay is
+  where `MTU = 1420` comes from, and the empty native-routing CIDR is why pod→LAN is masqueraded
+  today.
+- **`WG_CLIENT_CIDR` collides with nothing.** Pod CIDR `10.0.0.0/16` (`CLUSTER_POD_CIDR`), service
+  CIDR `10.43.0.0/16` (measured: `kubernetes` Service clusterIP is `10.43.0.1`), the PIA tunnel's
+  `10.72.192.0/18` (`platform/vpn-egress/README.md`), and both LANs `192.168.1.0/24` /
+  `192.168.2.0/24`. `10.90.0.0/24` is outside all five.
+- **The egress-class label matters and is set to `internet`.** Read live:
+  `CiliumEgressGatewayPolicy vpn-egress-steering` selects `podSelector:
+  homelab.keithjackson.dev/egress-class: vpn` with **no namespace scope**, so `vpn` here would have
+  steered every remote client's internet traffic out PIA.
+- **All three nodes are untainted** (`spec.taints: None` on each), so the DaemonSet covers the
+  cluster with no tolerations.
+- **`new-peer.sh` was run end to end** against a throwaway server key in the scratchpad (deleted
+  immediately after; it never existed in the repo). It rendered a correct profile — `Address
+  10.90.0.7/32`, `DNS 192.168.2.23`, `Endpoint wan.home.keithjackson.dev:51820`, `MTU 1420`,
+  `PersistentKeepalive 25`, `AllowedIPs 0.0.0.0/0` — at mode 0600, printed the matching public-key
+  stanza, and both argument-validation paths (missing name, out-of-range octet) refuse correctly.
+  The private key was redacted from every line I displayed.
+- **The endpoint name is resolver-independent, which is the specific trap this avoids.**
+  `wan.${BASE_DOMAIN}` is an unproxied public Cloudflare A record kept current by
+  `platform/externaldns/ddns.yaml` (checked every 5 min), so it resolves from a cellular connection
+  — unlike any name PiHole answers, which a remote client cannot resolve until it is already
+  connected. (This is the `plex.direct` lesson applied.)
+- **Velero does cover this namespace.** `platform/velero/helmrelease.yaml`'s `daily` schedule
+  excludes only `monitoring` and `unifi`, so `vpn-ingress` and the `wg-server-key` Secret are
+  captured off-cluster to R2. Read from the manifest, not from a backup listing.
+
+## What I did NOT verify
+
+- **THE ACTUAL FIX. Nothing in this branch has been proven to carry a single packet.** The
+  DaemonSet has never been reconciled, no `wg0` has ever existed, and no handshake has ever been
+  attempted. Three blockers are off-repo and manual (kernel module, server key, WAN forward), and
+  this branch removes none of them — it only makes them the *only* remaining work.
+- **Outside-in reachability, at all.** This repo has **no off-LAN vantage point**, which is exactly
+  the gap the plex remote-access work hit. Step 6 of the runbook (a phone on cellular) is the only
+  honest test and it has not been run.
+- **The in-pod `iptables` → host-netfilter interaction, which is my biggest single doubt.** Debian 13
+  uses nf_tables; the container writes MASQUERADE/FORWARD rules into the **host's** tables via the
+  image's own `iptables`. If that binary is the legacy backend while the host is nft, the rules can
+  apply to a table the kernel does not consult — and the symptom would be the nastiest available:
+  handshakes succeed, `wg show` looks perfect, and every forwarded connection hangs. **Check this
+  first if the tunnel comes up but nothing is reachable:** `iptables-save -t nat | grep MASQUERADE`
+  and `nft list table ip nat` on the node, from the host, not from the pod.
+- **Whether `allowPrivilegeEscalation: false` is compatible with the image's s6 init.** It is the
+  correct posture and I set it, but this repo has already been bitten by `no-new-privileges`
+  misbehaving (`platform/externaldns/ddns.yaml`'s README note). If the pod fails before
+  `wg-quick` runs, that flag is the first thing to try flipping.
+- **Whether `NET_ADMIN` alone is sufficient.** Reasoned from what `wg-quick` does (create the link,
+  set a sysctl, write two netfilter rules), not measured. If `iptables` complains, `NET_RAW` is the
+  likely addition — deliberately not granted pre-emptively.
+- **The image's custom-config path.** `lscr.io/linuxserver/wireguard:1.0.20260223-r0-ls124` (tag
+  confirmed to exist and to be the current one, published 2026-10-01) is expected to bring up
+  whatever is in `/config/wg_confs/` when `PEERS` is unset. That is its documented behaviour; it has
+  not been run here, and the init container's assembly of that file has never executed.
+- **Whether the probe is right.** `wg show wg0` is asserted to exit non-zero when the interface is
+  absent. Not executed.
+- **Cilium's reaction to a new `wg0` in the host netns.** `platform/cilium/values.yaml` does not pin
+  `devices`, so Cilium auto-detects; whether it attaches to `wg0` — and whether that matters — is
+  unknown. `wg` interfaces are already filtered out by `node_health_collect.py`, so something in
+  the estate anticipates them, but that is not evidence about Cilium.
+- **The CI approval-policy outcome.** The local stage reported green, but that is an offline N/A,
+  not a verdict: this PR touches `clusters/**`, so CI will block pending an override.
+- **Zero peers means the end-to-end authorisation path is untested**, including revocation. The
+  first enrolment is also the first test of `peers.yaml`'s format being what `wg-quick` accepts.
+- **No peer-level observability exists.** An exporter publishing
+  `wireguard_latest_handshake_seconds` is the top follow-up; until then "who is connected" is an
+  on-demand `wg show` and nothing alerts on an unexpected session. Pod-down is covered only by
+  kube-prometheus-stack's generic `KubePodNotReady` / `KubeDeploymentReplicasMismatch`, which I did
+  not confirm fire for a DaemonSet in this namespace.
+- **The security consequence I am most keen for a human to review rather than take from me:** an
+  enrolled device reaches the three k3s nodes themselves — apiserver 6443, kubelet 10250, SSH 22 —
+  because "reach the entire local network" includes them. That is stated in the README and the
+  runbook with the narrowing recipe, but it is a posture decision, not a verified fact, and it is
+  the right thing to argue about on this PR.