---
date: 2026-10-04
branch: feat/hubble-flow-export-plex
title: Record the pre-SNAT client address for Plex via Hubble static flow export, instead of breaking externalTrafficPolicy to get it
---

## What changed

Operator requirement, narrowed explicitly: **this is 100% about log visibility** — knowing which
address connected to Plex. Not bandwidth metering, which does not matter here.

**The problem, measured.** Plex's own log cannot show it. Every LoadBalancer Service in this cluster
is `externalTrafficPolicy: Cluster`, so the node holding the L2 lease for the VIP SNATs the client
before forwarding to the backend pod:

| Measured 2026-10-04 | Value |
|---|---|
| Node announcing `192.168.2.24` | `k3s-prod-3` (also holds `.20` Gateway, `.23` pihole-dns) |
| Node running the Plex pod | `k3s-prod-1` (`10.0.0.135`) |
| Sources in Plex's log | **3,214 × `10.0.1.x`**, 105 × `10.0.2.x`, 120 × loopback |
| `192.168.x` sources in Plex's log, ever | **0** |
| `X-Forwarded-For` in Plex's log | **0** (it serves raw tcp/32400, not HTTP via the Gateway) |
| `10.0.1.78` identity (`cilium-dbg bpf ipcache`) | `identity=1` → `reserved:host` = prod-3 itself |

**Nothing on the router is involved** — the operator correctly pointed out there is no hairpin NAT
here. The rewrite is entirely in-cluster, done by Cilium's BPF load-balancer on the lease holder,
because the backend pod is on a different node.

**The address is not lost, only unrecorded.** Cilium observes the flow at ingress, *before* its own
translation, so Hubble already holds the true source:

    192.168.2.133 -> 10.0.0.135    (real LAN client -> the Plex pod)
    10.0.1.78     -> 10.0.0.135    (the same traffic post-SNAT — what Plex sees)

What was missing is **retention**: the ring buffer was **4095/4095 flows at ~303 flows/s — about
thirteen seconds of history** — with hubble metrics disabled and no exporter configured.

So: enable the static flow exporter, scoped to Plex's port, writing to the agent's stdout.

- **`platform/cilium/helmrelease.yaml`** (authoritative): `hubble.export.static.enabled: true`,
  `filePath: stdout`, `allowList` of `{"destination_port":["32400"]}` and
  `{"source_port":["32400"]}`.
- **`platform/cilium/values.yaml`** (reference mirror) and
  **`infra/ansible/roles/cilium/templates/cilium-values.yaml.j2`** (the `[parity]` source of truth):
  the same block, so a bootstrap render does not differ from what Flux reconciles — a mismatch would
  be a permanent Helm diff and an avoidable agent rollout.

**`filePath: stdout`, not a file,** because Grafana Alloy already runs as a DaemonSet tailing every
pod's logs into Loki (`platform/monitoring/alloy.yaml`). stdout therefore reaches Loki with **no new
hostPath mount, no file-rotation handling, and no Alloy change at all**. Upstream documents the
value: *"To get Hubble flows directly exported to the logs instead of written to a rotated file,
`stdout` can be defined as `hubble-export-file-path`."* Query:

    {namespace="kube-system", app="cilium"} |= "32400"

**SCOPED BY PORT, NOT BY NAMESPACE — a measured decision, not a preference.** A
`--to-namespace plex` query returned **only the post-SNAT flows**; the flow carrying the real client
address did not match it, because at the point of observation the destination identity is not yet
resolved to the plex pod. A namespace filter would have dropped exactly the record this change
exists to capture.

**WHY NOT FIX THE SNAT INSTEAD — both alternatives rejected on evidence.**
- `externalTrafficPolicy: Local` would put the real address in Plex's own log, but cilium 1.20's L2
  announcer is **explicitly incompatible** with it. Upstream docs for this exact version:
  *"incompatible with the `externalTrafficPolicy: Local` on services as it may cause service IPs to
  be announced on nodes without pods causing traffic drops"* and *"L2 announcements isn't currently
  aware of this setting"*. Live proof it is not theoretical: the VIP is announced by prod-3 while the
  pod runs on prod-1, so the flip would black-hole tcp/32400 **immediately**. Making it safe means
  pinning both the pod and the announcement to one node and surrendering Plex's ability to
  reschedule — a real availability loss to buy a log field. Same trap
  `platform/crafty/service-l4.yaml` documents from an 8-day Minecraft outage.
- **DSR** also preserves the client address, but `routing-mode` here is **vxlan**, not
  native/geneve, and DSR returns bypass the ingress node, which breaks the SOHO router's stateful
  NAT on the remote path. Cluster-wide blast radius across all eight LB Services for one service's
  logging.

**A correction to the repo's own record.** `decisions/2026-10-03-plex-remote-access-l4.md` states the
SNAT puts the client inside `192.168.0.0/16` (the ingress node's LAN address), and I repeated that in
the previous entry. **It is wrong**: measured, the SNAT source is `10.0.1.x` — the node's
`cilium_host` inside the pod CIDR. This matters, because it means `LanNetworksBandwidth` can never
discriminate local from remote while eTP is `Cluster`: `10.0.0.0/8` must be in the LAN set for the
in-cluster consumers (Seerr) to count as local, and every external client arrives in that same range.
PR #48's LAN definition therefore fixes the Remote badge by making *everything* local — acceptable
only because metering is explicitly not a goal here.

## What I verified

Live prod, 2026-10-04, read-only.

- **Every measurement in the table above**, including the VIP-lease-to-node map
  (`cilium-dbg shell -- db/show l2-announce` on all three agents) and the pod's node.
- **Hubble already carries the pre-SNAT source** — the single finding this whole approach rests on:
  `hubble observe --port 32400` on the lease holder returned `192.168.2.133 -> 10.0.0.135` **and**
  its return flow, alongside the post-SNAT `10.0.1.78 -> 10.0.0.135`.
- **The retention gap is real:** `cilium-dbg status` reported `Hubble: Ok  Current/Max Flows:
  4095/4095 (100.00%), Flows/s: 303.62  Metrics: Disabled`, and the `cilium-config` ConfigMap
  contains no `hubble-export-*` key at all.
- **The namespace-filter trap**, directly: `--to-namespace plex` returned only `10.0.1.78` and
  `10.0.1.71`; the `192.168.2.133` flow was absent. This is why the allowList is port-scoped.
- **All eight LoadBalancer Services are `eTP=Cluster`** (crafty ×2, gateway, pihole-dns ×2, plex,
  unifi ×2) — so this is a cluster-wide pattern, not a Plex-specific choice.
- **The eTP:Local incompatibility is upstream-documented for v1.20 specifically**, quoted above from
  the docs for the running version — not inferred from the crafty incident.
- **`routing-mode: tunnel`** and **`bpf-lb-mode-annotation: false`** in the live `cilium-config`,
  which is what rules DSR out.
- **The chart's value paths and defaults**, read from cilium v1.20.1's own `values.yaml`:
  `hubble.export.static.{enabled,filePath,fieldMask,fieldAggregate,aggregationInterval,allowList,denyList,fileMaxSizeMb,fileMaxBackups,fileCompress}`,
  with `filePath` defaulting to `/var/run/cilium/hubble/events.log`. The keys used here exist.
- **Alloy's pipeline shape**, read from `platform/monitoring/alloy.yaml`: a DaemonSet with
  `loki.source.kubernetes "pods"` → `loki.process` → `loki.write` at
  `http://loki.monitoring.svc.cluster.local:3100`. It already tails kube-system pods, which is why
  stdout needs no Alloy change.
- **All three value files agree** (one `destination_port` occurrence each) and both YAML files parse,
  with `export.static` resolving to the intended object.
- **Toolbox gate**: **rc 3**, with `spec-immutability`, `decisions-log`, `lint`, `l0`,
  `render-golden`, `l1` and `approval-policy` all **pass**; rc 3 is the two known environmental skips
  (`gitea-settings` — no local `SETTINGS_API_TOKEN`; `conformance` L2/L3 — `CLUSTER_AVAILABLE`
  unset). **Not green. Reported as rc 3.**
- **No sensitive paths touched** — `platform/cilium/**` and `infra/ansible/**` are not in
  `infra/gitea/approval-policy.json`, so this needs no approval override, unlike PR #48.

## What I did NOT verify

- **THE OUTCOME. Nothing has been reconciled and no flow has ever been exported.** `cilium-config`
  still has no `hubble-export-*` key. Every claim is about inputs.
- **Whether `filePath: stdout` is accepted as written.** This is the single largest risk. The value
  comes from a verbatim upstream doc sentence (*"`stdout` can be defined as
  `hubble-export-file-path`"*), but I did not confirm the exact notation in cilium 1.20.1's source,
  and the chart default is a real filesystem path. If the literal string is not special-cased, the
  agent may create a FILE named `stdout` in its working directory and nothing reaches Loki — a
  silent no-op, not a crash. **Fallback if so:** leave `filePath` at the chart default and add a
  `local.file_match` + `loki.source.file` target to Alloy with a hostPath mount for
  `/var/run/cilium/hubble`.
- **Whether the FlowFilter JSON is accepted.** `{"destination_port":["32400"]}` follows the proto
  (`destination_port` is a repeated string) and the documented shape (`'{"verdict":["DROPPED"]}'`),
  but upstream gives **no port example** and I did not validate it against the running agent. A
  malformed filter could be rejected — or, worse, be silently treated as "no match" and export
  nothing.
- **THIS CHANGE ROLLS CILIUM.** Editing the HelmRelease restarts the agent DaemonSet across all
  three nodes. BPF maps are preserved so established traffic should survive, but prod-3 currently
  announces the Gateway VIP, **PiHole's DNS VIP** and Plex's VIP, so a lease change during the
  rollout could briefly interrupt LAN DNS for the whole house. Not measured, and worth doing at a
  quiet moment.
- **Log volume in practice.** Estimated "a few hundred to a few thousand lines a day" from the
  observed request counts; never measured as flows. Both directions are exported and no `fieldMask`
  is set, so each record is a full flow object. If it is noisy, narrow with `fieldMask` rather than
  by dropping a filter.
- **Loki's retention for this data**, and whether the `{namespace="kube-system", app="cilium"}` label
  set actually matches (it depends on the cilium pods carrying
  `app.kubernetes.io/name`, which Alloy maps to `app` — I did not confirm that label exists on the
  cilium DaemonSet pods). The query in the comment may need adjusting to `pod=~"cilium-.*"`.
- **That the exported flow actually contains the pre-SNAT address.** Hubble's *live* stream does
  (measured). I am assuming the exporter sees the same flow objects; I did not confirm the exporter
  is not fed a post-translation view.
- **The parity convention has no automated check.** I kept all three files in sync by hand because
  the comments demand it; nothing in `ci/` or `conformance/` verifies cilium Helm↔Ansible parity, so
  a future edit can still drift them silently.