Merge pull request 'feat(cilium): roll the agents when cilium-config changes (merged config was silently inert)' (#53) from feat/cilium-roll-out-on-config-change into main

Reviewed-on: #53

decisions/2026-10-05-cilium-roll-out-on-config-change.md

@@ -0,0 +1,88 @@
+---
+date: 2026-10-05
+branch: feat/cilium-roll-out-on-config-change
+title: Cilium config changes were silently inert — roll the agents when cilium-config changes, which also finally activates the Hubble exporter
+---
+
+## What changed
+
+**A merged Cilium config change did nothing, and everything reported success.** The Hubble flow
+exporter (PR #50, merged 2026-10-04) wrote its settings into `cilium-config` and never took effect.
+
+| Measured 2026-10-05, over a day after the merge | |
+|---|---|
+| HelmRelease `cilium` | `Ready=True`, `UpgradeSucceeded`, *"Helm upgrade succeeded for release kube-system/cilium.v6"* |
+| `cilium-config` keys | `hubble-export-file-path: stdout`, `hubble-export-allowlist: {"destination_port":["32400"]} {"source_port":["32400"]}` — **all present** |
+| cilium agent pods | **all three still the PRE-MERGE pods**, `startTime 2026-10-04T07:11Z` |
+| exported flow lines in agent stdout | **0, 0, 0** |
+| Flux Kustomizations | all `Ready=True` |
+
+Cause: the chart's `rollOutCiliumPods` defaults to **`false`** (cilium 1.20.1 `values.yaml`: *"Roll
+out cilium agent pods automatically when configmap is updated"*), so Helm rewrites the ConfigMap and
+leaves the DaemonSet's pod template untouched — and **cilium-agent reads that ConfigMap only at
+startup**. The feature was merged, believed delivered, green everywhere, and doing nothing at all.
+
+That is the same class of failure this repo already guards against elsewhere: a green signal sitting
+over something that never ran.
+
+- **`platform/cilium/helmrelease.yaml`** (authoritative): `rollOutCiliumPods: true`.
+- **`platform/cilium/values.yaml`** (reference mirror) and
+  **`infra/ansible/roles/cilium/templates/cilium-values.yaml.j2`** (the `[parity]` source of truth):
+  the same, so a bootstrap render does not differ from what Flux reconciles.
+
+**The cost is real and is the point.** Every future Cilium config change now triggers a cluster-wide
+agent rollout instead of waiting for someone to remember a manual restart. That is strictly more
+honest — the change applies when merged, or it fails visibly — but it makes config edits disruptive
+by default, so they want a quiet moment. Mitigation already in place:
+`updateStrategy.rollingUpdate.maxUnavailable: 1` means the DaemonSet will not proceed past an unready
+agent, so a bad render costs one node rather than the cluster.
+
+**Merging this is itself one rollout**, because adding the ConfigMap checksum annotation changes the
+pod template — and that rollout is what finally activates the Hubble exporter.
+
+## What I verified
+
+- **Every row of the table above**, read from the live HelmRelease status, the live `cilium-config`
+  ConfigMap, the agent pods' `startTime`, and a grep for `"flow"` in each agent's stdout.
+- **The chart value name, default and semantics**, quoted from cilium **v1.20.1**'s own
+  `values.yaml` — the version actually running here (`quay.io/cilium/cilium:v1.20.1`), not a guess
+  from another release: `rollOutCiliumPods: false` with the comment *"Roll out cilium agent pods
+  automatically when configmap is updated."*
+- **All three value files carry the key** and both YAML files still parse, with
+  `spec.values.rollOutCiliumPods` resolving to `true`.
+- **The blast-radius mitigation is genuinely present**, not assumed:
+  `updateStrategy.rollingUpdate.maxUnavailable: 1` is already set in the HelmRelease, with a long
+  existing comment explaining that a CNI rollout has no healthy-peer fallback.
+- **THE MECHANISM IS CONFIRMED BY CONTRAST, not just reasoned.** The cgroup fix (PR #42,
+  2026-10-03) DID take effect: both the DaemonSet and the running pod mount
+  `cilium-cgroup hostPath=/sys/fs/cgroup`, matching what the HelmRelease declares. The difference is
+  exactly the one claimed above — #42 changed the POD TEMPLATE (a volume hostPath), which rolls the
+  DaemonSet on its own, while #50 changed ONLY the ConfigMap, which does not. It also explains the
+  agents' `startTime 2026-10-04T07:11Z`: that was #42's rollout, and nothing has rolled them since.
+  So the inertness is specific to ConfigMap-only changes, which is precisely what this flag fixes.
+- **Flux is healthy before this change** — every Kustomization `Ready=True`, so this lands on a clean
+  graph rather than into an existing cascade.
+- **Toolbox gate**: recorded in the PR.
+
+## What I did NOT verify
+
+- **THE OUTCOME, ENTIRELY. Unreconciled.** No agent has rolled, no flow has been exported. This
+  change is an argument that the rollout will happen, not evidence that it did.
+- **Whether `filePath: stdout` actually works** — still the open question from #50, and it cannot be
+  answered until the agents restart. If the literal is not special-cased, the agent may create a
+  FILE named `stdout` and nothing reaches Loki: a silent no-op, not a crash. Fallback documented in
+  #50: keep the chart's default path and add a `loki.source.file` target to Alloy with a hostPath
+  mount. **Check for flow lines in the agent logs immediately after the rollout.**
+- **THE ROLLOUT'S IMPACT ON LAN DNS IS UNMEASURED AND IS THE MAIN RISK.** The node holding the L2
+  lease for the Gateway VIP, **PiHole's DNS VIP** and Plex's VIP loses them briefly as it cycles.
+  `maxUnavailable: 1` bounds it to one node at a time, and BPF maps persist across an agent restart,
+  but I have not measured how long a VIP is unreachable during a lease move, nor whether the two
+  PiHole replicas cover the gap. Merge it at a quiet moment.
+- **Whether enabling this is the operator's preferred trade.** The alternative — leaving it `false`
+  and restarting by hand — keeps config edits non-disruptive at the cost of them being silently
+  inert. I judged silent inertness the worse failure, but it is a judgement, not a measurement.
+- **Whether anything ELSE in `cilium-config` is currently inert.** I checked the one other recent
+  Cilium change and it is fine (see below), but I did not audit every key against the running
+  agents' actual state.
+- **`hubble.relay.rollOutPods` / `hubble.ui.rollOutPods`** are left at their `false` defaults. Both
+  have the same silently-inert property for their own ConfigMaps; not addressed here.

infra/ansible/roles/cilium/templates/cilium-values.yaml.j2

@@ -39,6 +39,12 @@ bpf:
   masquerade: true
 
 # Flow observability / isolation audit (ADR-0002).
+# Roll the agents when cilium-config changes. Kept EQUAL to the Flux values
+# (platform/cilium/helmrelease.yaml), which carry the full rationale: the chart default of false
+# leaves the pod template untouched on a config change, and cilium-agent reads that ConfigMap only
+# at startup, so the change is silently inert until someone restarts the DaemonSet by hand.
+rollOutCiliumPods: true
+
 hubble:
   enabled: true
   relay:

platform/cilium/helmrelease.yaml

@@ -188,6 +188,37 @@ spec:
         enabled: false
       hostRoot: /sys/fs/cgroup
     # --- Agent rollout: ONE node at a time (blast-radius bound) — 2026-09-01 incident ---
+    # --- Roll the agents when their ConfigMap changes (2026-10-05) ---
+    # [parity] MUST equal Ansible: rollOutCiliumPods: true
+    #
+    # WHY: a merged Cilium config change DID NOTHING. The chart default is `false`
+    # (cilium 1.20.1 values.yaml: "Roll out cilium agent pods automatically when configmap is
+    # updated. rollOutCiliumPods: false"), so Helm rewrites `cilium-config` and leaves the
+    # DaemonSet's pod template untouched — and cilium-agent reads that ConfigMap only at STARTUP.
+    # The result is a silently inert change: Flux green, HelmRelease `UpgradeSucceeded`, the new
+    # keys visibly present in the ConfigMap, and the running agents still on the old settings
+    # until a human remembers to restart them.
+    #
+    # MEASURED, and it is why this exists: the Hubble flow exporter merged 2026-10-04 wrote
+    # `hubble-export-file-path: stdout` and its allowlist into `cilium-config`, the HelmRelease
+    # reported `Helm upgrade succeeded ... cilium.v6`, and over a DAY later all three agents were
+    # still the pre-merge pods (startTime 2026-10-04T07:11Z) with ZERO exported flow lines. The
+    # feature was merged, believed delivered, and doing nothing at all. That is the same class of
+    # failure this repo already documents elsewhere — a green signal over something that never ran.
+    #
+    # THE COST IS REAL AND IS THE POINT: every future Cilium config change now triggers a
+    # cluster-wide agent rollout instead of waiting for a manual restart. That is strictly more
+    # honest — the change applies when it is merged, or it fails visibly — but it means config
+    # edits are disruptive by default, so they want a quiet moment. One node at a time:
+    # `updateStrategy.rollingUpdate.maxUnavailable: 1` below means the DaemonSet will not proceed
+    # past an unready agent, so a bad render costs one node rather than the cluster. Note that the
+    # node holding the L2 lease for the Gateway, PiHole-DNS and Plex VIPs loses them briefly as it
+    # cycles, so a rollout can blip LAN DNS.
+    #
+    # ENABLING THIS IS ITSELF ONE ROLLOUT: adding the ConfigMap checksum annotation changes the pod
+    # template, so merging this rolls the agents once — which is what finally activates the Hubble
+    # exporter that has been inert since 2026-10-04.
+    rollOutCiliumPods: true
     # [parity] MUST equal Ansible: updateStrategy.rollingUpdate.maxUnavailable: 1.
     # The chart's own default is 2 (cilium 1.20.1 values.yaml: updateStrategy.rollingUpdate.
     # maxUnavailable: 2) — NOT a local choice, and on a 3-node cluster that lets a single bad

platform/cilium/values.yaml

@@ -32,6 +32,15 @@ enableIPv4Masquerade: true
 bpf:
   masquerade: true
 # [parity] flow observability / isolation audit
+# [parity] roll the agents when cilium-config changes. The chart default (false) rewrites the
+# ConfigMap but leaves the pod template alone, and cilium-agent only reads it at STARTUP — so a
+# merged config change is SILENTLY INERT. Measured 2026-10-04..05: the Hubble exporter keys were
+# live in cilium-config and the HelmRelease said UpgradeSucceeded, while all three agents were
+# still pre-merge pods exporting nothing for over a day. Cost: config edits now roll the agents
+# (one node at a time via maxUnavailable: 1), which can briefly blip the VIPs on the lease-holding
+# node. Full rationale in helmrelease.yaml.
+rollOutCiliumPods: true
+
 hubble:
   enabled: true
   relay: