infra/docs/adr/0014-service-identity-and-east-west-observability.md

status	date
accepted	2026-06-24

Service identity is namespace + label; east-west observability via Calico Goldmane; no service mesh

As the Service count grows we want an audit-grade record of which Service talks to which — the "service mesh evaluation" docs/plans/2026-04-20-infra-audit-design.md flagged as never done ("worth a design doc even if the answer is no, too much complexity for the gain"). We evaluated the full design space against two constraints: the trust model is a single-tenant cluster needing attribution-grade forensics (reconstruct events in a cluster we trust), not cryptographic non-repudiation against a hostile pod; and we are acutely etcd-constrained (we removed VPA/Goldilocks for exactly this, and carry open beads code-oflt/code-at4f on etcd starvation). Decision: service identity = the workload's namespace (primary; Goldmane stamps it natively and "one Service ≈ one namespace" holds for ~87 of our namespaces), refined by an explicit service-identity label only in the few genuinely multi-Service namespaces (monitoring, kube-system, dbaas). East-west observability = Calico 3.30 Goldmane + Whisker (already in our Calico v3.30.7, currently enabled = false in stacks/calico/main.tf), with Goldmane's emitter shipping flows to Loki for a durable trail. Enforcement reuses the existing Wave 1 observe-then-enforce egress track, now selecting on namespace/label and fed by Goldmane's allow/deny + policy-trace flows. We explicitly reject a service mesh, mTLS, SPIFFE/SPIRE, and dedicated per-Service ServiceAccounts for now.

Considered options

• Dedicated per-Service ServiceAccount as the identity primitive — initially chosen, then reversed. 56% of pods (257/458) run as default, so it is a ~116-stack rollout; and Goldmane (the chosen flow source) carries pod/namespace/workload labels but no ServiceAccount field, so SAs would not even reach the audit trail without a custom pod→SA mapping. The cheaper, etcd-inert path (namespace is free; a handful of static labels) delivers the same attribution. Deferred until identity-aware NetworkPolicy needs a principal finer than namespace/label, or mTLS is adopted.
• Service mesh (Istio / Linkerd / Cilium-mesh) + mTLS + SPIFFE/SPIRE — the only thing that makes the trail cryptographically non-repudiable against a hostile pod. The trust model does not justify it, east-west stays single-tenant plaintext, and it is precisely the "too much complexity for the gain" the audit doc predicted. Rejected.
• Microsoft Retina (CNI-agnostic eBPF) — more capable (DNS, drops, Hubble UI) and GA, runs on Calico without a CNI change. But identity-rich mode writes one RetinaEndpoint CRD per pod to etcd (continuous, pod-proportional churn — the exact axis we guard), and it is metrics-first, not log-first (no per-flow Loki records without custom glue). Rejected for this use case; noted as the fallback if DNS/drop-level detail is ever needed.
• Cilium Hubble — reads Cilium's eBPF datapath maps; unusable on Calico without migrating the CNI. A CNI migration is not justified. Rejected.
• Kiali — builds its graph entirely from an Istio mesh's Prometheus telemetry; no mesh, no graph. Rejected.
• Custom Grafana Alloy enrichment exporter over raw iptables-LOG flow lines — Alloy has no IP→identity dictionary-lookup primitive (loki.process lacks a lookup stage; k8sattributes can't do per-line/dual-IP association), so this is a multi-day custom build that also has to beat pod-IP churn. Goldmane delivers identity-stamped flows natively and obviates it. Rejected.
• Kyverno generate+mutate to provision/assign identity — rejected on etcd grounds: background scans + PolicyReports + UpdateRequests are continuous writes, the VPA-class cost we shed. Identity stays static.

Consequences

• No etcd cost from the flow plane. Goldmane streams flows from Felix (the existing calico-node DaemonSet) over gRPC into a ~60-minute in-memory ring buffer — nothing written to etcd or the K8s API. Steady-state cost is two Deployments (goldmane, whisker) + RAM/CPU on the goldmane pod.
• The ring buffer is not a trail. Durable, queryable history depends on the emitter→Loki path (reuse the 90-day security-stream retention); on a Goldmane restart the in-memory window is lost.
• Goldmane is tech-preview in OSS Calico 3.30 — the main risk. Enabling it is a reversible toggle in stacks/calico/main.tf, but the toggle interacts with the operator-managed Installation CR (only namespaces are TF-adopted today; verify how Goldmane/Whisker are enabled before applying).
• Attribution is namespace-grained for free across ~87 single-Service namespaces. Multi-Service namespaces (monitoring, kube-system, dbaas) need a service-identity label to disambiguate; most are platform/infra and already on the Wave 1 enforcement exclude list.
• The trail is attribution-grade, not cryptographic. It reliably reconstructs events in a trusted cluster but cannot prove identity against a pod that spoofs its source — an accepted limit of the trust model. This ADR does not change the east-west encryption posture (still plaintext, no mTLS).
• Enforcement gains a better data source. Goldmane's allow/deny + policy-trace flows build the Wave 1 empirical egress allowlist faster than the current iptables-LOG→journald→Loki path, and policies select on namespace/label with no SA dependency.
• New ubiquitous language recorded in CONTEXT.md: Service identity and Goldmane / Whisker.
• Revisit triggers: adopt dedicated per-Service SAs if identity-aware NetworkPolicy needs a principal finer than namespace/label, or if mTLS is ever required; reconsider Retina if DNS/drop-level flow detail becomes necessary.