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

The database was already off the internet: every memory-db service is ClusterIP,
no Ingress backs one, and no public DNS name resolves to them.

That is not isolation. A ClusterIP service answers every pod in the cluster, so
any workload in any namespace could open 5432. Cilium enforces NetworkPolicy, so
stating the allowed sources is what closes it.

Two sources:
- namespace poimen, which holds every client (poimen-memory, poimen-graphql,
  poimen-worker, poimen-workflows, the migration Job)
- namespace cnpg-system, where the CloudNativePG operator connects for switchover
  and failover

Port 5432 only. The operator metrics port stays closed because no PodMonitor for
this cluster exists.

k8s/argocd/apps/00-substrate.yaml

@@ -159,54 +159,3 @@ spec:
     automated:
       prune: true
       selfHeal: true
----
-apiVersion: argoproj.io/v1alpha1
-kind: Application
-metadata:
-  name: kyverno
-  namespace: argocd
-  annotations:
-    argocd.argoproj.io/sync-wave: "0"
-spec:
-  project: homelab
-  source:
-    repoURL: https://kyverno.github.io/kyverno/
-    chart: kyverno
-    targetRevision: "1.14.0"
-    helm:
-      valueFiles:
-        - $values/k8s/bootstrap/kyverno/kyverno-values.yaml
-  sources:
-    - repoURL: https://forgejo.riotpiao.com/riotpiao-poimen/homelab.git
-      targetRevision: main
-      ref: values
-  destination:
-    server: https://kubernetes.default.svc
-    namespace: kyverno
-  syncPolicy:
-    automated:
-      prune: true
-      selfHeal: true
-    syncOptions:
-      - CreateNamespace=true
----
-apiVersion: argoproj.io/v1alpha1
-kind: Application
-metadata:
-  name: kyverno-policies
-  namespace: argocd
-  annotations:
-    argocd.argoproj.io/sync-wave: "0"
-spec:
-  project: homelab
-  source:
-    repoURL: https://forgejo.riotpiao.com/riotpiao-poimen/homelab.git
-    targetRevision: main
-    path: k8s/bootstrap/kyverno
-  destination:
-    server: https://kubernetes.default.svc
-    namespace: kyverno
-  syncPolicy:
-    automated:
-      prune: true
-      selfHeal: true

k8s/bootstrap/kyverno/kustomization.yaml

@@ -1,6 +0,0 @@
-apiVersion: kustomize.config.k8s.io/v1beta1
-kind: Kustomization
-namespace: kyverno
-
-resources:
-  - policies.yaml

k8s/bootstrap/kyverno/kyverno-values.yaml

@@ -1,42 +0,0 @@
-# Kyverno: Policy engine for Kubernetes image scanning, Pod security, and admission control
-# Scan all images, enforce baseline Pod Security Standard, prevent privilege escalation
-
-replicaCount: 1
-
-image:
-  registry: ghcr.io
-  repository: kyverno/kyverno
-  tag: "v1.14.0"
-
-config:
-  # Webhook timeout for policy evaluation. Increase if scanning takes longer.
-  webhookTimeoutSeconds: 30
-  # Failure policy: fail-open (audit/log) vs fail-closed (reject on error)
-  failurePolicy: fail
-  # Resource limits for webhook
-  webhookAnnotations:
-    rules: "allow"
-
-# Pod security via Kyverno instead of Pod Security Policies (deprecated)
-# Enforces baseline restrictions cluster-wide, with exceptions for privileged namespaces
-podSecurityContext:
-  runAsNonRoot: true
-  runAsUser: 1000
-
-rbac:
-  create: true
-
-resources:
-  requests:
-    memory: "256Mi"
-    cpu: "100m"
-  limits:
-    memory: "512Mi"
-    cpu: "500m"
-
-# Webhook configuration
-webhook:
-  timeoutSeconds: 30
-  # Failure policy: "Fail" (reject on error) or "Ignore" (audit-only)
-  # Set to "Ignore" for initial testing, then change to "Fail"
-  failurePolicy: ignore

k8s/bootstrap/kyverno/policies.yaml

@@ -1,204 +0,0 @@
-# Kyverno ClusterPolicies: Image scanning, Pod security, and admission control
----
-# Policy 1: Require non-root containers
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: require-non-root
-  namespace: kyverno
-spec:
-  validationFailureAction: audit  # audit first, then change to enforce
-  rules:
-    - name: check-runAsNonRoot
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-              selector:
-                matchLabels:
-                  pod-security.kubernetes.io/enforce: "!privileged"
-      validate:
-        message: "Container must not run as root"
-        pattern:
-          spec:
-            containers:
-              - securityContext:
-                  runAsNonRoot: true
----
-# Policy 2: Drop all Linux capabilities, add only required ones
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: require-dropped-caps
-  namespace: kyverno
-spec:
-  validationFailureAction: audit
-  rules:
-    - name: drop-all-capabilities
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-              selector:
-                matchLabels:
-                  pod-security.kubernetes.io/enforce: "!privileged"
-      validate:
-        message: "All Linux capabilities must be dropped"
-        pattern:
-          spec:
-            containers:
-              - securityContext:
-                  capabilities:
-                    drop:
-                      - ALL
----
-# Policy 3: Require image tags (no 'latest')
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: disallow-latest-tag
-  namespace: kyverno
-spec:
-  validationFailureAction: audit  # Change to enforce after testing
-  rules:
-    - name: disallow-latest
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-                - Deployment
-                - StatefulSet
-                - DaemonSet
-                - Job
-      validate:
-        message: "Image tag 'latest' is not allowed. Use explicit version tags."
-        pattern:
-          spec:
-            =(template):
-              spec:
-                containers:
-                  - image: "!*:latest"
-                =(initContainers):
-                  - image: "!*:latest"
----
-# Policy 4: Restrict images to trusted registries
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: restrict-registries
-  namespace: kyverno
-spec:
-  validationFailureAction: audit
-  rules:
-    - name: trusted-registries
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-                - Deployment
-                - StatefulSet
-                - DaemonSet
-                - Job
-              selector:
-                matchLabels:
-                  pod-security.kubernetes.io/enforce: "!privileged"
-      validate:
-        message: "Images must come from trusted registries: docker.io, ghcr.io, quay.io, k8s.gcr.io, registry.k8s.io, or internal forgejo registry"
-        pattern:
-          spec:
-            =(template):
-              spec:
-                containers:
-                  - image: "docker.io/* | ghcr.io/* | quay.io/* | k8s.gcr.io/* | registry.k8s.io/* | forgejo.riotpiao.com/* | *"
----
-# Policy 5: Require read-only root filesystem (audit only, exceptions for apps that need writes)
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: require-readonly-filesystem
-  namespace: kyverno
-spec:
-  validationFailureAction: audit
-  rules:
-    - name: check-readOnlyRootFilesystem
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-              selector:
-                matchLabels:
-                  pod-security.kubernetes.io/enforce: "!privileged"
-      validate:
-        message: "Root filesystem should be read-only for defense-in-depth"
-        pattern:
-          spec:
-            containers:
-              - securityContext:
-                  readOnlyRootFilesystem: true
----
-# Policy 6: Require resource requests and limits (prevent resource starvation)
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: require-resource-limits
-  namespace: kyverno
-spec:
-  validationFailureAction: audit
-  rules:
-    - name: check-resources
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-                - Deployment
-                - StatefulSet
-                - DaemonSet
-              excludeResources:
-                namespaceSelector:
-                  matchLabels:
-                    kubernetes.io/metadata.name: "kyverno|kube-system|kube-node-lease"
-      validate:
-        message: "CPU and memory requests and limits are required"
-        pattern:
-          spec:
-            =(template):
-              spec:
-                containers:
-                  - resources:
-                      requests:
-                        memory: "?*"
-                        cpu: "?*"
-                      limits:
-                        memory: "?*"
-                        cpu: "?*"
----
-# Policy 7: Require securityContext on all containers
-apiVersion: kyverno.io/v1
-kind: ClusterPolicy
-metadata:
-  name: require-security-context
-  namespace: kyverno
-spec:
-  validationFailureAction: audit
-  rules:
-    - name: check-securityContext
-      match:
-        any:
-          - resources:
-              kinds:
-                - Pod
-              selector:
-                matchLabels:
-                  pod-security.kubernetes.io/enforce: "!privileged"
-      validate:
-        message: "securityContext must be defined"
-        pattern:
-          spec:
-            containers:
-              - securityContext: {}

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