Merge pull request 'feat(cilium): export Plex's pre-SNAT client address via Hubble, scoped to tcp/32400' (#50) from feat/hubble-flow-export-plex into main
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---
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date: 2026-10-04
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branch: feat/hubble-flow-export-plex
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title: Record the pre-SNAT client address for Plex via Hubble static flow export, instead of breaking externalTrafficPolicy to get it
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---
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## What changed
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Operator requirement, narrowed explicitly: **this is 100% about log visibility** — knowing which
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address connected to Plex. Not bandwidth metering, which does not matter here.
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**The problem, measured.** Plex's own log cannot show it. Every LoadBalancer Service in this cluster
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is `externalTrafficPolicy: Cluster`, so the node holding the L2 lease for the VIP SNATs the client
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before forwarding to the backend pod:
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| Measured 2026-10-04 | Value |
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|---|---|
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| Node announcing `192.168.2.24` | `k3s-prod-3` (also holds `.20` Gateway, `.23` pihole-dns) |
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| Node running the Plex pod | `k3s-prod-1` (`10.0.0.135`) |
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| Sources in Plex's log | **3,214 × `10.0.1.x`**, 105 × `10.0.2.x`, 120 × loopback |
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| `192.168.x` sources in Plex's log, ever | **0** |
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| `X-Forwarded-For` in Plex's log | **0** (it serves raw tcp/32400, not HTTP via the Gateway) |
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| `10.0.1.78` identity (`cilium-dbg bpf ipcache`) | `identity=1` → `reserved:host` = prod-3 itself |
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**Nothing on the router is involved** — the operator correctly pointed out there is no hairpin NAT
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here. The rewrite is entirely in-cluster, done by Cilium's BPF load-balancer on the lease holder,
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because the backend pod is on a different node.
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**The address is not lost, only unrecorded.** Cilium observes the flow at ingress, *before* its own
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translation, so Hubble already holds the true source:
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192.168.2.133 -> 10.0.0.135 (real LAN client -> the Plex pod)
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10.0.1.78 -> 10.0.0.135 (the same traffic post-SNAT — what Plex sees)
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What was missing is **retention**: the ring buffer was **4095/4095 flows at ~303 flows/s — about
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thirteen seconds of history** — with hubble metrics disabled and no exporter configured.
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So: enable the static flow exporter, scoped to Plex's port, writing to the agent's stdout.
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- **`platform/cilium/helmrelease.yaml`** (authoritative): `hubble.export.static.enabled: true`,
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`filePath: stdout`, `allowList` of `{"destination_port":["32400"]}` and
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`{"source_port":["32400"]}`.
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- **`platform/cilium/values.yaml`** (reference mirror) and
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**`infra/ansible/roles/cilium/templates/cilium-values.yaml.j2`** (the `[parity]` source of truth):
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the same block, so a bootstrap render does not differ from what Flux reconciles — a mismatch would
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be a permanent Helm diff and an avoidable agent rollout.
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**`filePath: stdout`, not a file,** because Grafana Alloy already runs as a DaemonSet tailing every
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pod's logs into Loki (`platform/monitoring/alloy.yaml`). stdout therefore reaches Loki with **no new
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hostPath mount, no file-rotation handling, and no Alloy change at all**. Upstream documents the
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value: *"To get Hubble flows directly exported to the logs instead of written to a rotated file,
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`stdout` can be defined as `hubble-export-file-path`."* Query:
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{namespace="kube-system", app="cilium"} |= "32400"
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**SCOPED BY PORT, NOT BY NAMESPACE — a measured decision, not a preference.** A
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`--to-namespace plex` query returned **only the post-SNAT flows**; the flow carrying the real client
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address did not match it, because at the point of observation the destination identity is not yet
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resolved to the plex pod. A namespace filter would have dropped exactly the record this change
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exists to capture.
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**WHY NOT FIX THE SNAT INSTEAD — both alternatives rejected on evidence.**
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- `externalTrafficPolicy: Local` would put the real address in Plex's own log, but cilium 1.20's L2
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announcer is **explicitly incompatible** with it. Upstream docs for this exact version:
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*"incompatible with the `externalTrafficPolicy: Local` on services as it may cause service IPs to
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be announced on nodes without pods causing traffic drops"* and *"L2 announcements isn't currently
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aware of this setting"*. Live proof it is not theoretical: the VIP is announced by prod-3 while the
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pod runs on prod-1, so the flip would black-hole tcp/32400 **immediately**. Making it safe means
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pinning both the pod and the announcement to one node and surrendering Plex's ability to
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reschedule — a real availability loss to buy a log field. Same trap
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`platform/crafty/service-l4.yaml` documents from an 8-day Minecraft outage.
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- **DSR** also preserves the client address, but `routing-mode` here is **vxlan**, not
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native/geneve, and DSR returns bypass the ingress node, which breaks the SOHO router's stateful
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NAT on the remote path. Cluster-wide blast radius across all eight LB Services for one service's
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logging.
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**A correction to the repo's own record.** `decisions/2026-10-03-plex-remote-access-l4.md` states the
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SNAT puts the client inside `192.168.0.0/16` (the ingress node's LAN address), and I repeated that in
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the previous entry. **It is wrong**: measured, the SNAT source is `10.0.1.x` — the node's
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`cilium_host` inside the pod CIDR. This matters, because it means `LanNetworksBandwidth` can never
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discriminate local from remote while eTP is `Cluster`: `10.0.0.0/8` must be in the LAN set for the
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in-cluster consumers (Seerr) to count as local, and every external client arrives in that same range.
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PR #48's LAN definition therefore fixes the Remote badge by making *everything* local — acceptable
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only because metering is explicitly not a goal here.
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## What I verified
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Live prod, 2026-10-04, read-only.
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- **Every measurement in the table above**, including the VIP-lease-to-node map
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(`cilium-dbg shell -- db/show l2-announce` on all three agents) and the pod's node.
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- **Hubble already carries the pre-SNAT source** — the single finding this whole approach rests on:
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`hubble observe --port 32400` on the lease holder returned `192.168.2.133 -> 10.0.0.135` **and**
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its return flow, alongside the post-SNAT `10.0.1.78 -> 10.0.0.135`.
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- **The retention gap is real:** `cilium-dbg status` reported `Hubble: Ok Current/Max Flows:
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4095/4095 (100.00%), Flows/s: 303.62 Metrics: Disabled`, and the `cilium-config` ConfigMap
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contains no `hubble-export-*` key at all.
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- **The namespace-filter trap**, directly: `--to-namespace plex` returned only `10.0.1.78` and
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`10.0.1.71`; the `192.168.2.133` flow was absent. This is why the allowList is port-scoped.
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- **All eight LoadBalancer Services are `eTP=Cluster`** (crafty ×2, gateway, pihole-dns ×2, plex,
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unifi ×2) — so this is a cluster-wide pattern, not a Plex-specific choice.
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- **The eTP:Local incompatibility is upstream-documented for v1.20 specifically**, quoted above from
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the docs for the running version — not inferred from the crafty incident.
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- **`routing-mode: tunnel`** and **`bpf-lb-mode-annotation: false`** in the live `cilium-config`,
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which is what rules DSR out.
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- **The chart's value paths and defaults**, read from cilium v1.20.1's own `values.yaml`:
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`hubble.export.static.{enabled,filePath,fieldMask,fieldAggregate,aggregationInterval,allowList,denyList,fileMaxSizeMb,fileMaxBackups,fileCompress}`,
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with `filePath` defaulting to `/var/run/cilium/hubble/events.log`. The keys used here exist.
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- **Alloy's pipeline shape**, read from `platform/monitoring/alloy.yaml`: a DaemonSet with
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`loki.source.kubernetes "pods"` → `loki.process` → `loki.write` at
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`http://loki.monitoring.svc.cluster.local:3100`. It already tails kube-system pods, which is why
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stdout needs no Alloy change.
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- **All three value files agree** (one `destination_port` occurrence each) and both YAML files parse,
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with `export.static` resolving to the intended object.
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- **Toolbox gate**: **rc 3**, with `spec-immutability`, `decisions-log`, `lint`, `l0`,
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`render-golden`, `l1` and `approval-policy` all **pass**; rc 3 is the two known environmental skips
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(`gitea-settings` — no local `SETTINGS_API_TOKEN`; `conformance` L2/L3 — `CLUSTER_AVAILABLE`
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unset). **Not green. Reported as rc 3.**
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- **No sensitive paths touched** — `platform/cilium/**` and `infra/ansible/**` are not in
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`infra/gitea/approval-policy.json`, so this needs no approval override, unlike PR #48.
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## What I did NOT verify
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- **THE OUTCOME. Nothing has been reconciled and no flow has ever been exported.** `cilium-config`
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still has no `hubble-export-*` key. Every claim is about inputs.
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- **Whether `filePath: stdout` is accepted as written.** This is the single largest risk. The value
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comes from a verbatim upstream doc sentence (*"`stdout` can be defined as
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`hubble-export-file-path`"*), but I did not confirm the exact notation in cilium 1.20.1's source,
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and the chart default is a real filesystem path. If the literal string is not special-cased, the
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agent may create a FILE named `stdout` in its working directory and nothing reaches Loki — a
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silent no-op, not a crash. **Fallback if so:** leave `filePath` at the chart default and add a
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`local.file_match` + `loki.source.file` target to Alloy with a hostPath mount for
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`/var/run/cilium/hubble`.
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- **Whether the FlowFilter JSON is accepted.** `{"destination_port":["32400"]}` follows the proto
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(`destination_port` is a repeated string) and the documented shape (`'{"verdict":["DROPPED"]}'`),
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but upstream gives **no port example** and I did not validate it against the running agent. A
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malformed filter could be rejected — or, worse, be silently treated as "no match" and export
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nothing.
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- **THIS CHANGE ROLLS CILIUM.** Editing the HelmRelease restarts the agent DaemonSet across all
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three nodes. BPF maps are preserved so established traffic should survive, but prod-3 currently
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announces the Gateway VIP, **PiHole's DNS VIP** and Plex's VIP, so a lease change during the
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rollout could briefly interrupt LAN DNS for the whole house. Not measured, and worth doing at a
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quiet moment.
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- **Log volume in practice.** Estimated "a few hundred to a few thousand lines a day" from the
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observed request counts; never measured as flows. Both directions are exported and no `fieldMask`
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is set, so each record is a full flow object. If it is noisy, narrow with `fieldMask` rather than
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by dropping a filter.
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- **Loki's retention for this data**, and whether the `{namespace="kube-system", app="cilium"}` label
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set actually matches (it depends on the cilium pods carrying
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`app.kubernetes.io/name`, which Alloy maps to `app` — I did not confirm that label exists on the
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cilium DaemonSet pods). The query in the comment may need adjusting to `pod=~"cilium-.*"`.
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- **That the exported flow actually contains the pre-SNAT address.** Hubble's *live* stream does
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(measured). I am assuming the exporter sees the same flow objects; I did not confirm the exporter
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is not fed a post-translation view.
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- **The parity convention has no automated check.** I kept all three files in sync by hand because
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the comments demand it; nothing in `ci/` or `conformance/` verifies cilium Helm↔Ansible parity, so
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a future edit can still drift them silently.
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@@ -45,6 +45,20 @@ hubble:
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enabled: true
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ui:
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enabled: true
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# Static flow export -> cilium-agent stdout. Kept EQUAL to the Flux values
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# (platform/cilium/helmrelease.yaml), which carry the full rationale: it records the PRE-SNAT
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# client address for Plex's raw tcp/32400, which Plex itself cannot log because every
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# LoadBalancer Service here is externalTrafficPolicy: Cluster and the VIP lease holder SNATs the
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# client. Present here so a BOOTSTRAP render does not differ from what Flux reconciles -- a
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# mismatch would show up as a permanent Helm diff and an avoidable agent rollout. Scoped by PORT,
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# not namespace: the flow carrying the real client address does not match a namespace filter.
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export:
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static:
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enabled: true
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filePath: stdout
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allowList:
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- '{"destination_port":["32400"]}'
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- '{"source_port":["32400"]}'
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# Ingress VIP announcement on the NAT LAN. IP pool / CiliumL2AnnouncementPolicy
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# (from the reserved 10.73.0.240-.250 range) is authored by WS-NET in Phase 2.
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@@ -101,6 +101,60 @@ spec:
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enabled: true
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ui:
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enabled: true # exposure gated behind oauth2-proxy forward-auth later (ADR-0014)
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# --- STATIC FLOW EXPORT: persist the PRE-SNAT client address for Plex (2026-10-04) ---
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# [parity] MUST equal Ansible: hubble.export.static.{enabled,filePath,allowList}
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#
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# WHY THIS EXISTS. Plex's own log cannot show who connected. Every LoadBalancer Service in
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# this cluster is `externalTrafficPolicy: Cluster`, so the node holding the L2 lease for the
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# VIP SNATs the client before forwarding to the backend pod. Measured 2026-10-04: Plex had
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# logged 3,214 requests from `10.0.1.x` (the lease holder k3s-prod-3's own address, Cilium
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# identity 1 = reserved:host) and ZERO from any 192.168.x address, ever. No X-Forwarded-For
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# either -- it serves raw tcp/32400, not HTTP through the Gateway.
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#
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# THE ADDRESS IS NOT LOST, ONLY UNRECORDED. Cilium observes the flow at ingress, BEFORE its
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# own translation, so Hubble already has the true source. Measured on the lease holder:
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# 192.168.2.133 -> 10.0.0.135 (real LAN client -> the Plex pod)
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# 10.0.1.78 -> 10.0.0.135 (the same traffic, post-SNAT -- what Plex sees)
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# What was missing is RETENTION: the ring buffer was 4095/4095 flows at ~303 flows/s, i.e.
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# about THIRTEEN SECONDS of history, with hubble metrics disabled and no exporter configured.
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#
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# WHY NOT FIX THE SNAT INSTEAD. `externalTrafficPolicy: Local` would preserve the address in
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# Plex's own log, but cilium 1.20's L2 announcer is explicitly incompatible with it -- upstream
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# docs for this exact version: "incompatible with the externalTrafficPolicy: Local on services
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# as it may cause service IPs to be announced on nodes without pods causing traffic drops",
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# and "L2 announcements isn't currently aware of this setting". Live proof that this is not
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# theoretical: the VIP is announced by k3s-prod-3 while the pod runs on k3s-prod-1, so the
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# flip would black-hole tcp/32400 immediately. Making it safe would mean pinning BOTH the pod
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# and the announcement to one node and giving up Plex's ability to reschedule -- a real
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# availability loss to buy a log field. (It is the same trap platform/crafty/service-l4.yaml
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# documents from an 8-day Minecraft outage.) DSR was also rejected: routing-mode here is
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# vxlan, not native/geneve, and DSR returns bypass the ingress node, which breaks the SOHO
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# router's stateful NAT on the remote path.
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#
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# `filePath: stdout` RATHER THAN A FILE, deliberately. Grafana Alloy already runs as a
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# DaemonSet tailing every pod's logs into Loki (platform/monitoring/alloy.yaml), so stdout
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# reaches Loki with NO new hostPath mount, no file-rotation handling and no Alloy change.
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# Upstream documents it: "To get Hubble flows directly exported to the logs instead of written
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# to a rotated file, `stdout` can be defined as `hubble-export-file-path`." fileMaxSizeMb /
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# fileMaxBackups are therefore left at chart defaults and do not apply.
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# Query: {namespace="kube-system", app="cilium"} |= "32400"
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#
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# SCOPED BY PORT, NOT BY NAMESPACE -- and that is a measured decision, not a preference. A
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# `--to-namespace plex` query returned ONLY the post-SNAT flows; the flow carrying the real
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# client address did NOT match it, because at the point of observation the destination
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# identity is not yet resolved to the plex pod. Filtering by namespace would therefore drop
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# exactly the record this change exists to capture. Port it is.
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#
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# Both directions are listed so the return path is captured too. Volume is small (a few
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# hundred to a few thousand lines a day); if it ever becomes noisy, narrow it with
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# `fieldMask` rather than by removing a filter.
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export:
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static:
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enabled: true
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filePath: stdout
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allowList:
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- '{"destination_port":["32400"]}'
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- '{"source_port":["32400"]}'
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# --- L2 announcement for the ingress VIP on the flat LAN (docs/09, OQ-1 resolved) ---
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# [parity] MUST equal Ansible: l2announcements.enabled: true. IP pool +
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# CiliumL2AnnouncementPolicy (reserved 10.73.0.240-.250) authored by WS-NET in Phase 2.
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@@ -38,6 +38,18 @@ hubble:
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enabled: true
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ui:
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enabled: true
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# [parity] static flow export -> cilium-agent stdout -> Alloy -> Loki. Records the PRE-SNAT
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# client address for Plex's raw tcp/32400, which Plex's own log cannot show (every LB Service here
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# is externalTrafficPolicy: Cluster, so the VIP lease holder SNATs the client). Scoped BY PORT,
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# not namespace: the flow carrying the real client IP does not match a namespace filter. Full
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# rationale, measurements and the rejected alternatives are in helmrelease.yaml.
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export:
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static:
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enabled: true
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filePath: stdout
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allowList:
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- '{"destination_port":["32400"]}'
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- '{"source_port":["32400"]}'
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# [parity] ingress VIP announcement on the flat LAN (docs/09, OQ-1)
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l2announcements:
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enabled: true
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Reference in new issue
Block a user