helm-charts/patchmon/templates/patchmon.networkpolicy.yaml

{{- /*
NetworkPolicy for patchmon (Gitea #5).

PatchMon has three outbound dependencies and all three arrive as connection
details inside 1Password items the chart never parses: Postgres, Redis and an
OIDC provider. So the egress rules name the STANDARD ports (5432, 6379, 443)
and nothing else, and a deployment whose dependency sits elsewhere is blocked
until networkPolicy.egress.extraPorts says so.

Note the pod label this policy selects: the bare release-and-chart name,
without the -deployment suffix most charts here use.

WHAT THIS OBJECT IS: a ceiling on reachability, not an authentication layer.
Only the ports declared below are reachable at all - whatever else the process
binds, now or after the next app update, is blocked without anyone having to
notice it exists.

WHAT IT IS NOT:
  - EGRESS IS COARSE. A NetworkPolicy matches CIDRs and selectors and NEVER
    hostnames, so "only to the database host" cannot be expressed at all. This
    cluster's CNI is Canal (Flannel plus Calico for policy) and has no FQDN
    rule; Calico's GlobalNetworkSet could express one but would bind this chart
    to Calico, the same argument that kept implementation-specific objects out
    of the Gateway-API sweep (#114). Each egress rule therefore permits its
    PORT to any destination.
  - NOT A BOUNDARY WHERE THE CNI DOES NOT ENFORCE ONE. An unenforced policy is
    accepted by the API server and filters nothing, so everything reads as
    configured while nothing is filtered.
  - THE REASONING IS IN TEMPLATE COMMENTS, not in "#" comments: those are part
    of the rendered object, travel into the cluster and appear in every release
    diff. ci/run-networkpolicy-test.sh fails on a rendered "#".

THE PORT NUMBERS BELOW ARE POD PORTS, NEVER NODEPORTS. A NetworkPolicy is
evaluated at the pod's network interface, after kube-proxy has already
translated a NodePort to the targetPort, so a NodePort number here would match
nothing while looking strict - and, being the only rule for that port, would
block every inbound connection instead. ci/run-networkpolicy-test.sh asserts
every port here against the containerPorts of the pod spec this policy
selects.
*/ -}}
{{- if .Values.networkPolicy.enabled }}
{{- $np := .Values.networkPolicy }}
{{- $ns := .Release.Namespace }}
{{- $probeSources := $np.probeSources | default list }}
{{- $allowedNs := $np.allowedNamespaces | default list }}
{{- $ic := $np.ingressController | default dict }}
{{- $routed := .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
  labels:
    app: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
spec:
  {{- /*
  Selects this chart's workload. Note the label: it is the bare
  release-and-chart name with NO -deployment suffix, unlike most charts
  here - copying a selector from a neighbouring chart would match nothing
  and leave this policy filtering nothing at all, which is why
  ci/run-networkpolicy-test.sh holds it against the render.
  */}}
  podSelector:
    matchLabels:
      app: {{ .Release.Name }}-{{ .Chart.Name }}
  policyTypes:
    - Ingress
    {{- /*
    Egress is listed because there IS something to restrict: this workload
    needs DNS and the ports named below, and nothing else. A chart whose
    workload opens no outbound connection of its own must NOT list Egress -
    valkey is the example - because a rule that constrains nothing makes the
    object look stricter than it is.
    */}}
    - Egress
  ingress:
    {{- /*
    3000 - the only port this pod declares, the one the Service forwards 80 to, and
    the port all three probes address. The probe path.
    */}}
    - ports:
        - protocol: TCP
          port: 3000
      {{- if $probeSources }}
      {{- /*
      RESTRICTED, because the operator supplied probeSources. The kubelet's probes
      come from the IP of the WORKER NODE running the pod, so that address has to be
      in the list or the pod never becomes Ready - and a pod that is never Ready
      reads as a broken application rather than as a policy.

      The ingress controller is added to the same rule, or the Ingress goes dark the
      moment this list is filled.
      */}}
      from:
        - namespaceSelector:
            matchLabels:
              {{- /*
              Set by Kubernetes itself on every namespace (>= 1.21), so this needs no
              labelling work on a namespace this chart does not own.
              */}}
              kubernetes.io/metadata.name: {{ $ns }}
        {{- if and $routed $ic.namespace }}
        {{- /*
        ONE from-entry with TWO selectors, which is an AND: pods carrying these labels
        IN that namespace. Written as two list entries it would be an OR, and would
        open the port to every pod in kube-system.
        */}}
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: {{ $ic.namespace | quote }}
          {{- with $ic.podLabels }}
          podSelector:
            matchLabels:
              {{- toYaml . | nindent 14 }}
          {{- end }}
        {{- end }}
        {{- range $allowedNs }}
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: {{ . | quote }}
        {{- end }}
        {{- range $probeSources }}
        - ipBlock:
            cidr: {{ . | quote }}
        {{- end }}
      {{- else }}
      {{- /*
      NO "from" SELECTOR, WHICH MEANS OPEN - deliberately, and only inside the
      cluster, because this port carries no NodePort. The alternative was to guess
      the worker node CIDRs, and a wrong guess blocks every kubelet probe: the pod
      stays un-Ready, the rollout times out, and the cause looks like the
      application. An empty "from: []" would be worse than either - it allows
      everything too, but while reading as a restriction. Narrow it with
      networkPolicy.probeSources.
      */}}
      {{- end }}
  egress:
    {{- /*
    DNS, unconditionally. There is no value to switch this off, and that is
    deliberate: a knob whose only other setting breaks every name lookup in
    the pod is a trap and not a feature.
    */}}
    - ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53
    {{- /*
    PostgreSQL on the STANDARD port. The connection details live in a 1Password
    item the chart never parses, so this is the conventional port and not the
    configured one; a Postgres anywhere else is blocked and belongs in
    networkPolicy.egress.extraPorts.
    */}}
    - ports:
        - protocol: TCP
          port: 5432
    {{- /*
    Redis/Valkey on the STANDARD port, same reasoning as Postgres above: the URL
    sits in a secret this chart does not read.
    */}}
    - ports:
        - protocol: TCP
          port: 6379
    {{- /*
    Outbound HTTPS, for the OIDC provider: the chart fetches the issuer's
    configuration and exchanges tokens over it, and the issuer URL lives inside a
    1Password item the chart never parses. 443 to any destination is as narrow as
    this object gets for that - a hostname cannot appear in a NetworkPolicy. An
    issuer on another port (a CI dex on 5556) needs
    networkPolicy.egress.extraPorts.
    */}}
    - ports:
        - protocol: TCP
          port: 443
    {{- with $np.egress }}
    {{- with .extraPorts }}
    {{- /*
    Ports only, to any destination - see the header. This is the operator's
    escape hatch from the egress cap, and the only alternative to switching
    the whole policy off.
    */}}
    - ports:
        {{- range . }}
        - protocol: TCP
          port: {{ int . }}
        {{- end }}
    {{- end }}
    {{- end }}
{{- end }}