feat(poimen): restrict the memory database to its own namespace (#103)

Co-authored-by: rock <[email protected]>

k8s/infra/poimen/kustomization.yaml

@@ -6,6 +6,8 @@ kind: Kustomization
 # deployments (wave 0) are applied.
 resources:
   - memory-db.yaml
+  # ClusterIP alone is not isolation: every pod in the cluster can reach it.
+  - memory-db-netpol.yaml
   - poimen-sandbox-namespace.yaml
   - poimen-sandbox-quota.yaml
   - pi-session-netpol.yaml

k8s/infra/poimen/memory-db-netpol.yaml

@@ -0,0 +1,42 @@
+---
+# Keep the memory database reachable only from inside its own namespace.
+#
+# What this does NOT change: the database was already unreachable from the
+# internet. `memory-db-rw`, `memory-db-ro` and `memory-db-r` are ClusterIP
+# services, no Ingress backs them, and no public DNS name resolves to them.
+#
+# What it fixes: a ClusterIP service is reachable by EVERY pod in the cluster,
+# because Kubernetes has no implicit isolation. Cilium enforces NetworkPolicy, so
+# stating the allowed sources is what turns "not on the internet" into "not
+# reachable from another tenant's namespace".
+#
+# Two sources, both required:
+#  - the poimen namespace, which holds every client: poimen-memory, poimen-graphql,
+#    poimen-worker, poimen-workflows and the migration Job.
+#  - cnpg-system, where the CloudNativePG operator lives. It connects to the
+#    instance for switchover and failover, so a narrower rule breaks recovery.
+#
+# No other port is opened. The operator's metrics endpoint stays closed because no
+# PodMonitor for this cluster exists, so nothing scrapes it.
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: memory-db-ingress
+  namespace: poimen
+spec:
+  podSelector:
+    matchLabels:
+      cnpg.io/cluster: memory-db
+  policyTypes:
+    - Ingress
+  ingress:
+    - from:
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: poimen
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: cnpg-system
+      ports:
+        - protocol: TCP
+          port: 5432