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---
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date: 2026-10-17
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branch: fix/vpn-ingress-l2-lease-collision
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title: "WITHDRAWN: a node CAN reach a VIP it announces. My L2-lease diagnosis was wrong"
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---
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## What changed
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**This branch previously proposed a fix. That fix has been reverted in full. The diagnosis behind it
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was wrong.** What is left is documentation of what was actually measured, so the wrong conclusion is
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not re-derived — it is very easy to re-derive from `ip neigh` alone.
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### The claim, and how it died
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The earlier version of this entry claimed: *a node cannot reach a LoadBalancer VIP whose Cilium L2
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announcement lease it holds itself* — the announcer does not answer its own ARP request, the
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neighbour entry settles at `FAILED`, and packets to that VIP die before leaving the node. Because
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`platform/vpn-ingress` runs WireGuard on `hostNetwork` and MASQUERADEs remote clients to the node's
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own address, a VPN client was said to inherit that. The fix labelled the forwarded node and excluded
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that label from announcing, with two alerts and four promtool tests behind it.
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The claim makes a sharp prediction. After today's UPS power-cycle **all eight** `cilium-l2announce-*`
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leases are held by `k3s-prod-1` (gateway, pihole tcp+udp, crafty tcp+udp, unifi tcp+udp, plex) —
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the extreme case. The prediction was therefore that `k3s-prod-1` should reach **none** of the five
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VIPs and the other two nodes should reach **all**.
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**The prediction failed.** Measured from the host netns of the `wireguard` pod on each node:
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| | `k3s-prod-1` (holds all 8) | `k3s-prod-2` / `-3` (hold none) |
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|---|---|---|
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| `ip neigh show 192.168.2.20` | `FAILED`, no lladdr | `lladdr bc:e9:2f:7e:c4:a6 REACHABLE` |
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| `curl -k https://192.168.2.20/` | **`200` in 18 ms** | `200` in 13–40 ms |
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| `nc -z 192.168.2.20 443` | **OK** | OK |
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| `192.168.2.22:25565`, `.23:53`, `.24:32400` | **all OK / `200`** | all OK / `200` |
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| `192.168.2.21:8443` | FAIL | **FAIL** (both) |
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The asserted **cause is still present** today — `FAILED` on the holder, for all five VIPs — while the
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asserted **effect is absent**. That is sufficient to falsify the causal claim without having to
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explain anything else. The ARP asymmetry is real and reproducible; it is also **inert**.
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### Why it is inert
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No traffic path resolves a LoadBalancer VIP by ARP:
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* `cilium-dbg status --verbose` reports `KubeProxyReplacement: True [eno1 …, wg0 10.90.0.1]` and
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`Masquerading: BPF [eno1, wg0]` (Cilium v1.20.1, TCX attach, tunnel/vxlan). Cilium's LB datapath
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is attached to **`wg0` as well as `eno1`**, so a remote client's packet arriving on `wg0` for a VIP
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is DNAT'd **in BPF, before any route or neighbour lookup for the VIP**.
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* `cilium-dbg service list` programs `192.168.2.20:443 => 127.0.0.1:13606` — the shared Gateway's
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backend is a **node-local** Envoy socket, so every node serves that VIP without a LAN packet.
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* Host-originated traffic is socket-LB'd (`Socket LB: Enabled`, `bpf-lb-sock-hostns-only: true`),
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which is why `curl` succeeds on the holder. Discriminator: a real service port connects while a
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bogus one (`nc -z 192.168.2.20 9999`) fails, identically on all three nodes — service-aware DNAT,
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not wire traffic.
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### The two probes that misled me
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Both were cited as evidence in the previous version of this entry.
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* **`ip neigh` on its own.** `FAILED` on the holder is permanent and harmless, and is also a probing
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artefact: VIPs answer no ICMP, so a `ping` leaves a failed entry whether or not anything is wrong.
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* **`curl --interface wg0`.** The previous entry used this as the control that ruled out a
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host-netns artefact. It is not a control: it fails (`rc=28`) from **all three** nodes, including
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the two whose ARP for the VIP resolves perfectly. It is uncorrelated with lease holding, so it
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discriminates nothing.
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**The deeper error:** a MASQUERADEd client's packets are **forwarded** (netfilter `FORWARD`, then
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routing); everything runnable from the pod is **socket-originated**. Different hooks. A host-netns
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probe cannot measure the forwarded path in either direction — it reports success where the forwarded
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path might fail, and `--interface wg0` reports failure where it does not. Sharing a netns is not
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sharing a hook, and that is the assumption the original diagnosis rested on.
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### Files
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Reverted to `origin/main`: `platform-config/cilium/l2-announcement-policy.yaml`,
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`infra/ansible/roles/node_baseline/{defaults,tasks}/main.yml`,
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`infra/ansible/inventory/group_vars/k3s_prod/vars.yml`, `platform/monitoring/alerts.yaml`,
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`platform/monitoring/kube-prometheus-stack.yaml`, `runbooks/kustomization.yaml`. Deleted:
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`platform/monitoring/tests/vpn-ingress-l2.test.yaml`, `runbooks/vpn-ingress-l2-collision.md`.
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Kept, rewritten from scratch:
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* **`platform/vpn-ingress/README.md`** — two measured sections: the L2 table above with why it is
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inert and which probes lie, and the internet-egress facts below.
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* **`runbooks/vpn-remote-access.md`** — a triage section for the reported symptom ("LAN and cluster
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work, internet does not") that works outwards from the client profile, and a short section saying
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the L2 lease is a dead end, with the unifi `.21` note.
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**Nothing in `platform/vpn-ingress` or `infra/vpn-ingress` changed behaviourally. No code fix is
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proposed by this branch any more.**
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### The internet-routing report: no server-side fix was needed, and none was made
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The brief's prior was that `new-peer.sh` renders a split tunnel and that the operator wants a full
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one, to be added as a documented option. **That prior does not match the tree.** `new-peer.sh` has
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emitted `AllowedIPs = 0.0.0.0/0` **by default since the component's first commit** (`f92707f`,
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2026-10-05, confirmed with `git log -S`); `--split` is the opt-in, and
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`runbooks/vpn-remote-access.md:252-253` already documents both forms. So there is no full-tunnel
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feature to add, and adding a `WG_FULL_TUNNEL` knob would be a second switch for a default that
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already exists. **I deliberately shipped no code change here** — writing one would have meant
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inventing a fix for a symptom I could not reproduce (see below).
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The server side was measured end to end and is capable and correct, so the cause is in the client
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profile or the client. The triage section names the two candidates that fit the symptom exactly —
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a `--split` profile, and the IPv4-only `AllowedIPs` letting a dual-stack client prefer AAAA and
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leak public traffic outside the tunnel — each with a one-line test that settles it.
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## What I verified
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Measured live against prod, `kubectl --context k3s-prod --request-timeout=15s`, read-only, on
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2026-10-17:
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* **The lease distribution.** All eight `cilium-l2announce-*` leases held by `k3s-prod-1`
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(`.spec.holderIdentity`). The brief's observation reproduced; it had not moved again.
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* **The falsification, in full**, as tabulated above: 3 nodes x 5 VIPs, `ip neigh` + `nc -z` + a
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real `curl` for each. The holder reaches four of five VIPs; `.21` fails from everywhere.
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* **The socket-LB discriminator.** Real service port OK, bogus port FAIL, identically on all three
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nodes — so the successes are service-aware DNAT, not wire delivery.
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* **`curl --interface wg0` fails on all three nodes**, including non-announcing ones with
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`REACHABLE` neighbour entries. This is the measurement that destroys the original control.
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* **The datapath facts** quoted above from `cilium-dbg status --verbose` and
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`cilium-dbg service list` on `cilium-55jv8` (`k3s-prod-1`), plus `cilium-config`:
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`kube-proxy-replacement=true`, `enable-l2-announcements=true`, `enable-bpf-masquerade=true`,
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`routing-mode=tunnel`, `devices=` (empty, auto-detected). Cilium `v1.20.1` on all three.
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* **The VIP is not a local address and routes on-link.** `ip route get 192.168.2.20` →
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`dev eno1 src 192.168.2.10` on the holder; nothing in `table local`; `ip -4 addr` shows no VIP.
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So the 200 is not loopback delivery by the host stack — it is BPF.
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* **The internet path, server side, on all three nodes:** `/proc/sys/net/ipv4/ip_forward` = `1`
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(read, never written); `iptables -t nat -S POSTROUTING` carries
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`-s 10.90.0.0/24 ! -o wg0 -j MASQUERADE`; the preceding `CILIUM_POST_nat` chain is **empty with 0
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packets**, so it cannot short-circuit that rule; `FORWARD -i wg0` and `-o wg0` ACCEPT both
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present; `default via 192.168.2.1 dev eno1 onlink` intact; `ip route get 1.1.1.1` resolves via it;
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`curl http://1.1.1.1/` returns `301` from each node.
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* **The PIA / egress-gateway answer.** `platform/vpn-egress/egress-steering.yaml` selects by
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`podSelector` on `egress-class: vpn`; `platform/vpn-ingress/daemonset.yaml:130` labels this pod
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`egress-class: internet`; `tun0` exists on **`k3s-prod-3` only** (`10.150.192.3/18`), absent on
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`-1` and `-2`. So a full tunnel egresses the **house WAN**, and a client's apparent address is the
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home WAN IP, not PIA's.
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* **PiHole resolves public names** — `nslookup google.com 192.168.2.23` from the pod returned
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`142.250.113.138`.
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* **No client is connected, and none has been since the power-cycle.** `wg show wg0` lists the one
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enrolled peer (`10.90.0.2/32`) with **no endpoint and no handshake** on all three nodes, and both
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`FORWARD -i wg0` and the `MASQUERADE` rule read **0 packets / 0 bytes** on all three. The
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`wireguard` pods restarted 153 min ago (2 restarts, 11d old), which reset the counters.
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* **The full-tunnel default's age**, from `git log -S` on `new-peer.sh`: introduced in `f92707f`
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(2026-10-05) and never changed.
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* **The branch rebased cleanly** onto `origin/main` (`1a0b208`, PR #70 merged) with no conflicts.
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## What I did NOT verify
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|
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* **THE FORWARDED PATH IS STILL UNMEASURED, in both directions.** No client is connected, so I could
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not test what a real remote client does, and — as established above — **no probe runnable from the
|
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pod can substitute for it**. Specifically I did **not** prove that a forwarded client packet to a
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VIP is DNAT'd by Cilium's `wg0` program. That inference rests on `cilium-dbg` listing `wg0` as a
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LB device plus the node-local Gateway backend, not on an observed client packet. **It is the one
|
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remaining way the withdrawn diagnosis could be partly right** — if `wg0` BPF were somehow not in
|
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the forwarded path, forwarded traffic would need ARP and would die on the holder. I judge this
|
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unlikely but it is unproven. *To close it: connect a client, then from the node whose `wg show`
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shows the peer endpoint, watch `FORWARD -i wg0` and the `MASQUERADE` counters move while the
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client loads a cluster app — and repeat it on a node that holds leases and one that does not.*
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* **WHICH NODE THE ROUTER FORWARDS `udp/51820` TO IS UNDETERMINABLE RIGHT NOW**, for the same
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reason. **I need a client connected** to learn it; the router is unreadable from the cluster.
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* **I cannot reproduce or explain the 2026-10-08 measurements.** That entry recorded `nc -z` TCP
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failures correlated with lease holding across 15 node x VIP pairs. Today the same test passes.
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My leading hypothesis is **stale or incorrectly-programmed BPF LB state on `k3s-prod-1`**,
|
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rebuilt by today's full power-cycle — which would make the lease correlation coincidental. A
|
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competing hypothesis is that Cilium had not auto-detected `wg0` then (`devices` is empty, and
|
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`wg0` is created by this DaemonSet after Cilium starts). **Both are unproven, and neither is
|
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needed for the falsification** — the asserted cause is present today without its effect. I did not
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retro-measure anything, and I did not read Cilium's source or issue tracker.
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* **The operator's report cannot be a description of "right now."** No client has connected since
|
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the power-cycle (0 forwarded packets, no handshake on any node), so "clients can reach cluster
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services and the LAN but not the internet" must describe a session before the power-cycle or one
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that has since dropped. **I did not establish when it was observed, or with which profile.**
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* **THE INTERNET ROOT CAUSE IS NOT DIAGNOSED.** I proved the server side is *capable*; I did **not**
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find the fault, and I shipped no fix for it. The two candidates in the triage section (a
|
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`--split` profile; IPv6 preference leaking outside an IPv4-only `AllowedIPs`) are **reasoned, not
|
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measured**. *What I need:* the `AllowedIPs` line from the client's own profile — that one line
|
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decides split vs full and halves the search — and a connected client for step 2.
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* **Whether `--split` was in fact used for the enrolled peer.** The profile holds a private key and
|
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lives only on the operator's machine and the device; it is not in the repo, and I did not look for
|
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it. Server-side `AllowedIPs` is a `/32` source filter and says nothing about the client's routing.
|
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* **Whether `MTU = 1420` holds on a full-tunnel WAN path.** Not measured, and not measurable without
|
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a client. It is the standard 1500 − 60; a client behind PPPoE or CGNAT with a smaller path MTU
|
||||
would see large transfers hang while small requests succeed. The runbook's existing MTU note
|
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(drop to 1280) already covers the remedy.
|
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* **Adding `::/0` to `AllowedIPs` is untested advice.** The triage section offers it to blackhole
|
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IPv6 rather than leak it, and states that the tunnel has no IPv6 egress. I did not try it on a
|
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client, and I do not know how each WireGuard client behaves when handed an IPv6 route on an
|
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interface with no IPv6 address.
|
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* **`192.168.2.21:8443` (unifi) fails from all three nodes**, as it did on 2026-10-08 — a separate,
|
||||
pre-existing fault. Not investigated, not addressed, and now recorded in the runbook as such.
|
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* **No runtime conformance.** `vars.CLUSTER_AVAILABLE` is still unset, so the gate proves the L0/L1
|
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offline subset only. Nothing above is covered by a test that runs in CI.
|
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* **Nothing was applied, and nothing needs to be.** The branch is now documentation-only, so there
|
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is no Flux reconcile, Ansible run or `kubectl` step to perform after merge. I ran no mutating
|
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`kubectl`, `flux` or Ansible, and did not run `new-peer.sh` (it mints key material).
|
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* I did not re-measure branch protection, runner state, or any other platform claim (CLAUDE.md §2b).
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@@ -0,0 +1,108 @@
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---
|
||||
date: 2026-10-18
|
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branch: fix/coredns-ha
|
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title: "coredns ran at one replica, so any node drain was a cluster-wide DNS outage"
|
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---
|
||||
|
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## What changed
|
||||
|
||||
**MEASURED on prod 2026-10-18: `kube-system/coredns` had `replicas: 1`.** In-cluster DNS was a
|
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single pod on a single node, so draining or rebooting that node was a **cluster-wide in-cluster DNS
|
||||
outage** until the pod rescheduled and became ready — every Service lookup, every CNPG replica
|
||||
finding its primary, every operator addressing the API by name. It was invisible because `1/1
|
||||
Ready` looks perfectly healthy.
|
||||
|
||||
It also became urgent rather than latent: the scheduled reboot automation on
|
||||
`feat/automated-upgrades` drains and reboots one node at a time, unattended, overnight — turning a
|
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single point of failure into a recurring one.
|
||||
|
||||
New `platform/coredns/hpa.yaml`: a `HorizontalPodAutoscaler` on the coredns Deployment with
|
||||
`minReplicas: 2`, `maxReplicas: 3`, registered in the existing `platform/coredns/kustomization.yaml`
|
||||
alongside the split-horizon ConfigMap already there.
|
||||
|
||||
**Why an HPA and not `replicas: 2` — this is the whole decision.** k3s owns the coredns Deployment
|
||||
and we cannot durably edit it: it is applied by k3s's own deploy controller from a bundled manifest
|
||||
(`AddOn/coredns`, source `/data/k3s/server/manifests/coredns.yaml`, `managedFields` managers
|
||||
`deploy@k3s-prod-1` and `k3s`, plus an `objectset.rio.cattle.io/hash` label). k3s re-stages its
|
||||
bundled manifests on startup, so a `replicas: 2` written there — or a `kubectl scale` — is reverted
|
||||
on the next k3s restart or upgrade. Two alternatives were weighed and rejected:
|
||||
|
||||
* **`coredns.yaml.skip` + our own templated copy** (the pattern `roles/kube_vip` already uses for a
|
||||
file in `server/manifests`). Deterministic and never flaps, but it takes ownership of coredns away
|
||||
from k3s permanently — k3s upgrades would stop updating it and the version would need refreshing
|
||||
by hand forever. Too high a price for a replica count.
|
||||
* **A Flux-managed patch of the Deployment.** Rejected outright: Flux and k3s's deploy controller
|
||||
would both own one object and fight continuously — the exact shape of the `default-deny`
|
||||
NetworkPolicy drift loop this cluster already suffered (~2500 events/10min).
|
||||
|
||||
An HPA avoids both: a separate object k3s does not own, driving the `/scale` subresource rather than
|
||||
the Deployment spec, so there is no shared-ownership fight. If k3s re-stages `replicas: 1`, the HPA
|
||||
sees it below `minReplicas` and scales back within one reconcile.
|
||||
|
||||
It is a **floor-holder, not an autoscaler**: the CPU metric exists only because an `autoscaling/v2`
|
||||
HPA needs one to be valid. `scaleDown.stabilizationWindowSeconds: 600` because DNS is the worst
|
||||
thing in the cluster to flap; `scaleUp` is immediate, since that is the path that restores redundancy
|
||||
after a k3s restart.
|
||||
|
||||
**Immediate action taken outside this PR:** `kubectl -n kube-system scale deploy coredns
|
||||
--replicas=2` was run at the operator's explicit request, so the cluster has two replicas **now**
|
||||
rather than after merge. That hand scale is what this PR makes durable.
|
||||
|
||||
## What I verified
|
||||
|
||||
* **The defect:** `kubectl -n kube-system get deploy coredns` → `replicas=1 available=1`.
|
||||
* **k3s ownership:** the `AddOn/coredns` object exists with source
|
||||
`/data/k3s/server/manifests/coredns.yaml`; the Deployment has no `ownerReferences` but carries
|
||||
`objectset.rio.cattle.io/hash` and `managedFields` managers `deploy@k3s-prod-1` / `k3s`. So it is
|
||||
k3s-managed, not Flux-managed — independently corroborated by another agent, which confirmed
|
||||
`platform/coredns/` contains **only** the `coredns-custom` ConfigMap and does not touch the
|
||||
Deployment or its replica count.
|
||||
* **The hand scale works and holds:** coredns went to `2/2 Running` on two different nodes, and
|
||||
in-cluster DNS kept answering throughout (`nslookup kubernetes.default.svc.cluster.local
|
||||
10.43.0.10` → `10.43.0.1`). Still `spec.replicas=2 ready=2` after ~2 minutes, with the AddOn
|
||||
checksum **unchanged** — so k3s's deploy controller does not revert on a drift timer; it
|
||||
re-applies on manifest change and on restart.
|
||||
* **The HPA's preconditions hold:** coredns ships `requests: {cpu: 100m, memory: 70Mi}` (so a
|
||||
Resource/Utilization metric is meaningful), and metrics-server is installed as a k3s addon and
|
||||
verified serving — `kubectl top pod -l k8s-app=kube-dns` returns **5m and 4m** against that 100m
|
||||
request, i.e. ~5% utilisation, confirming the 80% target will never be approached and the HPA will
|
||||
sit at `minReplicas`.
|
||||
* **The kustomization edit is additive:** `git diff --stat` is `1 file changed, 4 insertions(+)`,
|
||||
and `- coredns` was already registered in `platform/kustomization.yaml`, so no change was needed
|
||||
there.
|
||||
* All three touched/added YAML files parse.
|
||||
|
||||
## What I did NOT verify
|
||||
|
||||
* **The HPA has never been applied.** I did not reconcile it, so I have **not** observed it create,
|
||||
reach `ScalingActive=True`, resolve its metric against real coredns data, or hold `minReplicas`.
|
||||
Applying is an operator action (CLAUDE.md §5). The failure mode to watch for is
|
||||
`ScalingActive=False` with `FailedGetResourceMetric` — the HPA would then be present and inert,
|
||||
which looks identical to working because the hand scale already left 2 replicas in place. **Check
|
||||
`kubectl -n kube-system describe hpa coredns` after merge**, not just the replica count.
|
||||
* **The central claim that k3s reverts `replicas` on restart is REASONED, NOT OBSERVED.** It rests
|
||||
on k3s re-staging bundled manifests at startup plus the measured ownership evidence above. I did
|
||||
**not** restart k3s to watch the revert happen — doing so is a rolling control-plane restart, an
|
||||
operator action. If k3s in fact preserves a modified replica count, this HPA is unnecessary
|
||||
(though harmless).
|
||||
* **I did not confirm the HPA wins the race against k3s's deploy controller after a restart.** Both
|
||||
write the scale; the expectation is the HPA re-asserts within a reconcile, leaving a brief window
|
||||
at 1 replica. Neither the window's length nor the outcome has been measured.
|
||||
* **I nearly shipped a destructive change.** My first write of
|
||||
`platform/coredns/kustomization.yaml` replaced the file wholesale, listing only `hpa.yaml` — which
|
||||
would have pruned the existing `coredns-custom` ConfigMap and **broken in-cluster split-horizon
|
||||
DNS (R-DNS-01/03)**. It was caught by a guard assertion before commit and restored from `HEAD`, and
|
||||
the diff is now additive. Recorded because the near-miss is the useful part: `platform/coredns/`
|
||||
already existed and I assumed it did not. **No conformance check would obviously have caught the
|
||||
removal** — it is valid YAML and a legitimate-looking prune.
|
||||
* **Whether 2 is enough.** Three nodes, and coredns' anti-affinity only *prefers* spreading, so both
|
||||
replicas could in principle land on one node and a single drain would still take DNS down. I did
|
||||
not add a `topologySpreadConstraint` or a PodDisruptionBudget — both arguably belong here and
|
||||
neither is in this change.
|
||||
* **No alert fires if coredns drops to 1 replica**, so a future silent regression (k3s upgrade
|
||||
changing the manifest, the HPA going inert) would not be reported. That gap is not closed here.
|
||||
* **No conformance test asserts this**, so a future edit could remove the HPA with no gate stage
|
||||
noticing.
|
||||
* **No runtime conformance.** `vars.CLUSTER_AVAILABLE` is unset, so CI proves the L0/L1 offline
|
||||
subset only.
|
||||
* I did not re-measure branch protection or runner state (CLAUDE.md §2b).
|
||||
@@ -0,0 +1,112 @@
|
||||
---
|
||||
# =================================================================================================
|
||||
# coredns HA floor — hold in-cluster DNS at >= 2 replicas, which k3s does not.
|
||||
# =================================================================================================
|
||||
# MEASURED on prod 2026-10-18: `kube-system/coredns` ran with **replicas: 1**. In-cluster DNS is a
|
||||
# single pod on a single node, so **draining or rebooting that one node is a cluster-wide
|
||||
# in-cluster DNS outage** for as long as the pod takes to reschedule and become ready — every pod
|
||||
# that looks up a Service, every CNPG replica finding its primary, every operator talking to the
|
||||
# API by name. It is the single cheapest availability defect in the cluster, and it was invisible
|
||||
# because `1/1 Ready` looks perfectly healthy.
|
||||
#
|
||||
# This matters more now than it did: the reboot automation (kured + unattended-upgrades) drains and
|
||||
# reboots one node at a time on a schedule, which turns a latent single point of failure into a
|
||||
# recurring one, unattended, in the middle of the night.
|
||||
#
|
||||
# -------------------------------------------------------------------------------------------------
|
||||
# WHY AN HPA, AND NOT JUST `replicas: 2` — this is the whole decision
|
||||
# -------------------------------------------------------------------------------------------------
|
||||
# **k3s owns the coredns Deployment and we cannot durably edit it.** It is applied by k3s's own
|
||||
# deploy controller from a bundled manifest, not by Flux:
|
||||
#
|
||||
# $ kubectl -n kube-system get addon coredns
|
||||
# NAME SOURCE CHECKSUM
|
||||
# coredns /data/k3s/server/manifests/coredns.yaml 8cd91595...
|
||||
# $ kubectl -n kube-system get deploy coredns -o jsonpath='{.metadata.managedFields[*].manager}'
|
||||
# deploy@k3s-prod-1 k3s
|
||||
#
|
||||
# and the Deployment carries an `objectset.rio.cattle.io/hash` label — a wrangler objectset. k3s
|
||||
# RE-STAGES its bundled manifests on startup, so a `replicas: 2` written into that file (or a
|
||||
# `kubectl scale`) is reverted the next time k3s restarts or is upgraded. MEASURED the same day: a
|
||||
# hand `kubectl scale` to 2 was NOT actively reverted (it held, and the AddOn checksum did not
|
||||
# change) — the deploy controller re-applies on manifest change and on restart, not on a drift
|
||||
# timer. So the hand fix survives until exactly the event we are protecting against: a reboot.
|
||||
#
|
||||
# The two durable alternatives were weighed and rejected:
|
||||
# * **`coredns.yaml.skip` + our own templated copy** (the pattern roles/kube_vip already uses for
|
||||
# a manifest in server/manifests). Fully deterministic and never flaps — but it takes OWNERSHIP
|
||||
# of coredns away from k3s permanently, so k3s upgrades would stop updating it and the version
|
||||
# would have to be refreshed by hand forever. Too high a price for a replica count.
|
||||
# * **A Flux-managed patch of the Deployment itself.** Rejected outright: Flux and k3s's deploy
|
||||
# controller would both own one object and fight continuously. That is the shape of the
|
||||
# `default-deny` NetworkPolicy drift loop this cluster already suffered (Kyverno generate + Flux
|
||||
# both owning one resource, ~2500 events per 10 minutes).
|
||||
#
|
||||
# An HPA avoids both. It is a SEPARATE object that k3s does not own and will never reconcile away,
|
||||
# and it drives the Deployment's `/scale` subresource rather than its spec — so there is no
|
||||
# shared-ownership fight. If k3s re-stages `replicas: 1`, the HPA observes it under `minReplicas`
|
||||
# and scales back to 2 within one reconcile (~15s by default).
|
||||
#
|
||||
# THE COST, STATED PLAINLY: there is a brief window — seconds, after a k3s restart — where coredns
|
||||
# is back at 1 replica until the HPA notices. That is strictly better than the status quo, where it
|
||||
# is at 1 replica permanently, but it is not zero. Accepting that window is the trade being made
|
||||
# here; the `.skip` option above is what to reach for if it ever proves unacceptable.
|
||||
#
|
||||
# -------------------------------------------------------------------------------------------------
|
||||
# THIS IS A FLOOR-HOLDER, NOT A REAL AUTOSCALER
|
||||
# -------------------------------------------------------------------------------------------------
|
||||
# `minReplicas: 2` is the entire point. The CPU metric exists because an autoscaling/v2 HPA needs a
|
||||
# metric to be a valid object, not because coredns is expected to scale on load: measured via
|
||||
# metrics-server, the two pods use **5m and 4m** against a **100m** request — ~5% utilisation, so
|
||||
# the 80% target will never be approached and the HPA will sit at `minReplicas` indefinitely.
|
||||
#
|
||||
# The CPU request is what makes this legal: coredns ships `requests: {cpu: 100m, memory: 70Mi}`
|
||||
# (measured), and a Resource/Utilization metric is meaningless without a request. metrics-server is
|
||||
# installed as a k3s addon and verified serving (`kubectl top pod -l k8s-app=kube-dns` returns
|
||||
# figures), so the metric resolves rather than leaving the HPA with `ScalingActive=False`.
|
||||
#
|
||||
# `maxReplicas: 3` = the node count. coredns' pod anti-affinity prefers one pod per node, so a
|
||||
# fourth replica would add no failure-domain coverage; the ceiling exists so a metrics glitch can
|
||||
# never balloon DNS pods across the cluster.
|
||||
apiVersion: autoscaling/v2
|
||||
kind: HorizontalPodAutoscaler
|
||||
metadata:
|
||||
name: coredns
|
||||
# kube-system, because that is where k3s puts coredns. This is the only object this component
|
||||
# places outside a namespace it owns, and it is additive: it creates nothing in kube-system and
|
||||
# mutates only the coredns Deployment's scale subresource.
|
||||
namespace: kube-system
|
||||
labels:
|
||||
app.kubernetes.io/name: coredns
|
||||
spec:
|
||||
scaleTargetRef:
|
||||
apiVersion: apps/v1
|
||||
kind: Deployment
|
||||
name: coredns
|
||||
minReplicas: 2
|
||||
maxReplicas: 3
|
||||
metrics:
|
||||
- type: Resource
|
||||
resource:
|
||||
name: cpu
|
||||
target:
|
||||
type: Utilization
|
||||
# Deliberately high. See "floor-holder" above: this must not scale on normal DNS load.
|
||||
averageUtilization: 80
|
||||
behavior:
|
||||
scaleDown:
|
||||
# 10 minutes. DNS is the worst thing in the cluster to flap: a scale-down races in-flight
|
||||
# queries and every client's negative cache. The HPA should be reluctant in this direction.
|
||||
stabilizationWindowSeconds: 600
|
||||
policies:
|
||||
- type: Pods
|
||||
value: 1
|
||||
periodSeconds: 600
|
||||
scaleUp:
|
||||
# Prompt in the direction that restores redundancy — this is the path taken after a k3s
|
||||
# restart has re-staged `replicas: 1`.
|
||||
stabilizationWindowSeconds: 0
|
||||
policies:
|
||||
- type: Pods
|
||||
value: 2
|
||||
periodSeconds: 60
|
||||
@@ -7,3 +7,7 @@ apiVersion: kustomize.config.k8s.io/v1beta1
|
||||
kind: Kustomization
|
||||
resources:
|
||||
- coredns-custom.yaml
|
||||
# HA floor for the coredns Deployment itself — a separate concern from the split-horizon server
|
||||
# block above, and deliberately an HPA rather than a replica edit: k3s owns that Deployment via
|
||||
# its own deploy controller and re-stages `replicas: 1` on restart. hpa.yaml has the reasoning.
|
||||
- hpa.yaml
|
||||
@@ -186,86 +186,6 @@ right way; one was a defect in my own manifest.
|
||||
| Is the image's **iptables** backend compatible with the host's? | **Yes — both nft.** The image ships `iptables v1.8.13 (nf_tables)` via `xtables-nft-multi`, and Debian 13 is nf_tables. This was the documented worst fear (rules silently landing in a table the kernel does not consult); it is closed. |
|
||||
| Can the pod set **`net.ipv4.ip_forward`**? | **No, and it must not try.** `/proc/sys` is mounted **read-only** under `hostNetwork` (`proc /proc/sys proc ro,…`), because those are the host's globals; `sysctl -w` fails with EPERM whatever the capabilities. A failed `PostUp` is fatal to `wg-quick`, so this one line took the whole tunnel down. The node already has it set to `1`; the init container now **verifies** rather than writes. |
|
||||
|
||||
## Measured on prod, 2026-10-17 — L2 announcement does NOT affect what a client can reach
|
||||
|
||||
A change was proposed (PR #69) on the belief that **a node cannot reach a LoadBalancer VIP whose
|
||||
Cilium L2 announcement lease it holds**, and that the VPN node therefore had to be excluded from
|
||||
announcing. **That belief is wrong, and the change was withdrawn.** The half of it that is true is
|
||||
real but inert, and the distinction matters enough to record, because the wrong version is very
|
||||
easy to re-derive from `ip neigh` alone.
|
||||
|
||||
Measured with all **eight** `cilium-l2announce-*` leases held by `k3s-prod-1` — the extreme case,
|
||||
after the UPS power-cycle — from the host netns of the `wireguard` pod on each node:
|
||||
|
||||
| | `k3s-prod-1` (holds all 8) | `k3s-prod-2` / `-3` (hold none) |
|
||||
|---|---|---|
|
||||
| `ip neigh show 192.168.2.20` | `FAILED` (no lladdr) | `lladdr bc:e9:2f:7e:c4:a6 REACHABLE` |
|
||||
| `curl -k https://192.168.2.20/` | **`200`, 18 ms** | `200`, 13–40 ms |
|
||||
| `nc -z 192.168.2.20 443` | **OK** | OK |
|
||||
| plex `192.168.2.24:32400` | **`200`** | `200` |
|
||||
|
||||
So the announcer really does **not** answer its own ARP request — that part of the observation is
|
||||
reproducible. It changes nothing, because **no traffic path resolves a LoadBalancer VIP by ARP**:
|
||||
|
||||
* `cilium-dbg status --verbose` reports `KubeProxyReplacement: True [eno1 …, wg0 10.90.0.1]` and
|
||||
`Masquerading: BPF [eno1, wg0]`. Cilium's LB datapath is attached to **`wg0` as well as `eno1`**,
|
||||
so a remote client's packet arriving on `wg0` for a VIP is DNAT'd to a backend **in BPF, before
|
||||
any route or neighbour lookup for the VIP happens**.
|
||||
* `cilium-dbg service list` on `k3s-prod-1` programs `192.168.2.20:443 => 127.0.0.1:13606` — the
|
||||
shared Gateway's backend is a **node-local** Envoy socket. Every node can serve that VIP without
|
||||
a packet crossing the LAN at all.
|
||||
* Host-originated traffic is socket-LB'd (`Socket LB: Enabled`, `bpf-lb-sock-hostns-only: true`),
|
||||
which is why `curl` succeeds on the lease holder despite `FAILED`. The discriminator: a **real**
|
||||
service port connects, a **bogus** one (`nc -z 192.168.2.20 9999`) fails, on all three nodes —
|
||||
that is service-aware DNAT, not wire traffic.
|
||||
|
||||
**Two tests that look like proof and are not.** Both were used to support the withdrawn diagnosis:
|
||||
|
||||
* **`ip neigh` on its own.** `FAILED` on the holder is permanent and harmless. It is also an
|
||||
artefact of probing: VIPs answer no ICMP, so a `ping` leaves a failed entry behind whether or not
|
||||
anything is wrong.
|
||||
* **`curl --interface wg0`.** This fails (`rc=28`, timeout) from **all three** nodes, including the
|
||||
two whose ARP for the VIP resolves perfectly. It is not correlated with lease holding, so it
|
||||
discriminates nothing — and it is not the client path either (see below).
|
||||
|
||||
**Why neither probe can see the client path.** A MASQUERADEd remote client's packets are
|
||||
**forwarded** — netfilter `FORWARD`, then routing — whereas everything runnable from the pod is
|
||||
**socket-originated**. The two traverse different hooks, so a host-netns probe cannot measure the
|
||||
forwarded path in either direction: it reports success where the forwarded path might fail, and
|
||||
`--interface wg0` reports failure where it does not. **The forwarded path can only be measured with
|
||||
a client actually connected**, by watching the `FORWARD -i wg0` and `POSTROUTING … MASQUERADE`
|
||||
counters move.
|
||||
|
||||
## Measured on prod, 2026-10-17 — where a full tunnel's internet traffic actually egresses
|
||||
|
||||
`new-peer.sh` has emitted a **full tunnel** (`AllowedIPs = 0.0.0.0/0`) **by default since the
|
||||
component's first commit**; `--split` is the opt-in for LAN-only. There is no full-tunnel feature
|
||||
to add. The server side was checked end to end and is **capable and correct** — if a full-tunnel
|
||||
client cannot reach the internet, nothing in the list below is the reason:
|
||||
|
||||
| checked | result on all three nodes |
|
||||
|---|---|
|
||||
| `net.ipv4.ip_forward` (read from `/proc/sys`, never written) | `1` |
|
||||
| `iptables -t nat -S POSTROUTING` | carries `-s 10.90.0.0/24 ! -o wg0 -j MASQUERADE` — NATs to **any** outbound interface, so internet NAT needs no change |
|
||||
| `CILIUM_POST_nat`, which precedes it in the chain | **empty, 0 packets** — it cannot short-circuit the MASQUERADE |
|
||||
| `iptables -L FORWARD` | `-i wg0` and `-o wg0` ACCEPT both present |
|
||||
| default route | `default via 192.168.2.1 dev eno1 onlink`, intact |
|
||||
| node's own internet reachability | `http://1.1.1.1/` returns `301` |
|
||||
|
||||
**A full tunnel egresses the HOUSE WAN, not PIA.** This was the trap worth checking, and it is
|
||||
closed: `platform/vpn-egress/egress-steering.yaml`'s `CiliumEgressGatewayPolicy` selects by
|
||||
`podSelector` on `egress-class: vpn`, and this DaemonSet is deliberately labelled
|
||||
`egress-class: internet`, so it is not selected. Forwarded `wg0` traffic is not pod-identity
|
||||
traffic at all, and `tun0` exists on **`k3s-prod-3` only** (`10.150.192.3/18`) — the egress-gateway
|
||||
node. A remote client's apparent public address is therefore the **home WAN IP**, which is the
|
||||
intended behaviour and the thing to state when enrolling a device.
|
||||
|
||||
**Not measurable without a connected client.** At the time of writing `wg show wg0` listed the one
|
||||
enrolled peer with **no endpoint and no handshake** on every node, and both the `FORWARD -i wg0` and
|
||||
the `MASQUERADE` counters read **0 packets** — so no client traffic had been forwarded since the
|
||||
power-cycle, and which node the router forwards `udp/51820` to was **undeterminable**. Only the
|
||||
forwarded node shows a peer with an `endpoint` and a recent `latest handshake`.
|
||||
|
||||
## Prerequisites outside this directory
|
||||
|
||||
1. **The `wireguard` kernel module on every node.** Added to `node_baseline_kernel_modules`
|
||||
|
||||
@@ -273,84 +273,6 @@ bytes of WireGuard encapsulation); drop the client to `1280` and re-test.
|
||||
by design. Work inwards: `wg show` on the node holding the forward will show *zero* received bytes
|
||||
if the router is not delivering the packets, and a `handshake` with no completed session if it is.
|
||||
|
||||
## Triage — "the client reaches the LAN and cluster apps, but not the internet"
|
||||
|
||||
Reported 2026-10-17. Work **outwards from the client profile**, because that is where this symptom
|
||||
almost always lives, and because the server side has been measured and is not the cause.
|
||||
|
||||
**1. Read `AllowedIPs` in the client's own `[Peer]` stanza. This one line settles it.**
|
||||
|
||||
| the profile says | meaning |
|
||||
|---|---|
|
||||
| `0.0.0.0/0` | **full tunnel** — the default. Internet *should* be carried. Go to step 2. |
|
||||
| `192.168.2.0/24, 10.90.0.0/24` | **split tunnel** — `--split` was passed, or the profile predates the script. Internet never enters the tunnel **by design**; it uses the device's own uplink, and if that is broken the VPN cannot fix it. Re-render without `--split` to change it. |
|
||||
|
||||
`new-peer.sh` emits a full tunnel **by default** and has since the component's first commit —
|
||||
`--split` is the opt-in. There is no server-side switch for this: **it is a property of the client
|
||||
profile only**, so an already-issued profile keeps whatever it was rendered with until it is
|
||||
re-rendered and re-imported on the device. The two forms differ by one flag:
|
||||
|
||||
```bash
|
||||
./infra/devcontainer/dev.sh run bash -c './infra/vpn-ingress/new-peer.sh <name> <octet>' # full tunnel
|
||||
./infra/devcontainer/dev.sh run bash -c './infra/vpn-ingress/new-peer.sh <name> <octet> --split' # LAN only
|
||||
```
|
||||
|
||||
Re-rendering mints a **new keypair**, so it also needs the new `[Peer]` stanza PR'd into
|
||||
`peers.conf` and the old one deleted. Changing an existing device in place, without new keys, is
|
||||
editing `AllowedIPs` in the profile **on the device** — the server does not care.
|
||||
|
||||
**2. If it is a full tunnel, prove the client traffic is reaching the node at all.** Have the
|
||||
client connected, then watch the two counters that only forwarded traffic moves:
|
||||
|
||||
```bash
|
||||
./infra/devcontainer/dev.sh run bash -c \
|
||||
'kubectl --context k3s-prod -n vpn-ingress exec ds/wireguard -- sh -c "
|
||||
wg show wg0 endpoints; iptables -L FORWARD -n -v | head -5;
|
||||
iptables -t nat -L POSTROUTING -n -v | head -5"'
|
||||
```
|
||||
|
||||
* Only the **forwarded node** shows a peer with an `endpoint`; that is the only way to learn which
|
||||
node the router's `udp/51820` forward points at (the router is unreadable from the cluster).
|
||||
* `FORWARD -i wg0` at **0 packets** on every node means nothing is arriving — the problem is
|
||||
upstream of the cluster (router forward, client, or carrier), not here.
|
||||
* `FORWARD -i wg0` moving while `POSTROUTING … MASQUERADE` stays at **0** is the one server-side
|
||||
failure this symptom could have: un-SNATed `10.90.0.x` packets reach the router and die there,
|
||||
which breaks internet while node-local cluster VIPs still work. It has not been observed.
|
||||
|
||||
**3. Suspect DNS and address family before suspecting routing.** Both fit this symptom exactly:
|
||||
|
||||
* **IPv6.** `AllowedIPs = 0.0.0.0/0` carries **IPv4 only** (see Known limitations). A dual-stack
|
||||
client resolving a public name gets an AAAA, prefers IPv6, and sends it **outside** the tunnel —
|
||||
so LAN and cluster names (IPv4/RFC1918) work while public sites hang. Test by forcing IPv4:
|
||||
`curl -4 https://example.com` from the client. If `-4` works and plain `curl` hangs, this is it,
|
||||
and the fix is on the client (disable IPv6 on the tunnel, or add `::/0` to `AllowedIPs` so it is
|
||||
blackholed rather than leaked — note the tunnel has **no** IPv6 egress, so that blackholes it).
|
||||
* **PiHole.** The profile sets `DNS = 192.168.2.23`. It does resolve public names — verified
|
||||
2026-10-17, `google.com` answered from inside the cluster — but it is also an ad-blocker, so a
|
||||
blocked name is indistinguishable from "no internet" on one site. Test a name you know is not on
|
||||
a blocklist, and compare against `curl https://1.1.1.1/` by **IP**, which needs no DNS at all.
|
||||
|
||||
**4. What is NOT the cause.** Measured 2026-10-17, all three nodes: `ip_forward=1`; the
|
||||
`-s 10.90.0.0/24 ! -o wg0 -j MASQUERADE` rule present, with the preceding `CILIUM_POST_nat` chain
|
||||
**empty** so it cannot short-circuit it; `FORWARD -i/-o wg0` ACCEPT present; the default route
|
||||
`via 192.168.2.1 dev eno1` intact; and the nodes themselves reaching `1.1.1.1`. Also **not** the
|
||||
PIA egress gateway: it selects pods by `egress-class: vpn`, this DaemonSet is labelled
|
||||
`egress-class: internet`, and `tun0` exists on `k3s-prod-3` only — so a full tunnel egresses the
|
||||
**house WAN** and the client's apparent address is the **home WAN IP** (check 4 in step 6).
|
||||
|
||||
## Triage — which L2 announcement lease a node holds does NOT matter
|
||||
|
||||
Do not spend time here. It was investigated at length (PR #69, withdrawn) on the belief that a node
|
||||
could not reach a VIP it announced. Measured 2026-10-17 with **all eight** leases on `k3s-prod-1`:
|
||||
that node reached `192.168.2.20`, `.22`, `.23` and `.24` normally. The lease holder's `ip neigh`
|
||||
for its own VIP does sit at `FAILED` **permanently and harmlessly** — Cilium DNATs LoadBalancer
|
||||
VIPs in BPF on both `eno1` and `wg0` before any neighbour lookup, and the shared Gateway's backend
|
||||
is a node-local socket. Full measurements and the two misleading probes
|
||||
(`ip neigh`, `curl --interface wg0`) are in `platform/vpn-ingress/README.md`.
|
||||
|
||||
`192.168.2.21` (unifi) fails from **all three** nodes, including ones whose ARP resolves. That is a
|
||||
separate, pre-existing fault in that service and has nothing to do with the VPN.
|
||||
|
||||
## Revoking a device
|
||||
|
||||
Delete its `[Peer]` stanza from `peers.conf`, PR, merge. Nothing else — the key stops working on the
|
||||
|
||||
Reference in new issue
Block a user