feat!: NetworkPolicy in the NodePort and game-server charts, on by default

garage, minecraft-router, minecraft-server, samba, teamspeak-server,
satisfactory. One major each. These are the charts the plan said to leave for
last, and they earned it - three of them changed the convention rather than
just consuming it.

GARAGE is the clearest illustration after keycloak. Its four ports split three
ways: s3 and web are RESTRICTED by source (no probe touches them), admin is the
probe path and stays open inside the cluster - which is uncomfortable, because
admin is also the admin API, and that is said out loud instead of glossed - and
rpc gets the narrowest rule the object can express, a podSelector with no
namespaceSelector. All four numbers come from garage.settings.

MINECRAFT-SERVER is the tightest policy in the repository, and the reason is
worth knowing: all three of its probes are EXEC probes, which put no packet on
the network, so no port has to stay open for the kubelet and no probeSources
value is needed at all. RCON and metrics are restricted outright. The game port
has two branches rendered from the same value the Service reads -
server.service.type NodePort means players arrive from the internet and the
rule must be open; anything else means the only path is in-cluster, so the rule
is restricted and the router's namespace has to be in allowedNamespaces.

MINECRAFT-ROUTER derives its egress from the routing table instead of guessing:
server.backendPort plus the "port" override of every mapping that sets one. Add
a backend on a non-standard port and the policy follows. What it cannot express
is the destination - mappings name hosts, and this object matches no hostname -
so the rule is wider than the routing table, and that is written down.

SATISFACTORY gets policyTypes: [Ingress] and no egress section, and the second
half of the reason is the deciding one. Steam's content delivery is not a
pinnable port set (SteamCMD over TCP 80/443/27015-27050, master servers over
UDP 27000-27100 and 4380, changed by Valve, re-downloaded on every update) -
and this is the ONE chart with no install-test at all, because the image is
multiple GB and the first start pulls over 10GB. An egress cap here would be
the only one in the sweep with no empirical check behind it, on the chart whose
correct port set is least knowable.

SAMBA and TEAMSPEAK-SERVER carry the NodePort lesson explicitly: the rules name
445/139 and the pod's voice and file-transfer ports, never the NodePorts, and
teamspeak's file is explicit that its pod port and NodePort happening to share a
number is a coincidence of its values rather than a pattern to copy. Teamspeak's
voice rule is UDP, and the file says why that matters: a TCP rule on the same
number is accepted, looks complete, and drops every voice packet.

THREE THINGS THE CHECKS CAUGHT WHILE THIS BATCH WAS WRITTEN, all of them real:

  - minecraft-server's RCON rule named a port the pod does not declare. The
    containerPort is gated on server.rcon.enabled and the rule was not, so
    assertion 2 rejected it. The rule now carries the same gate.
  - samba and satisfactory would have shipped allowedNamespaces and
    probeSources values that reach NO rule - every one of their inbound rules
    is open to any source. A value that silently does nothing is worse than one
    that is absent, because it reads as a control, so both are gone from those
    two charts and from their schemas, with the reason in values.yaml.
    teamspeak-server loses probeSources for the same reason and keeps
    allowedNamespaces, which its web-query rule uses.
  - the policy templates no longer declare template variables they do not use.
    samba keeps one, satisfactory none.

Part of #5

minecraft-server/templates/minecraft-server.networkpolicy.yaml

@@ -0,0 +1,210 @@
+{{- /*
+NetworkPolicy for minecraft-server (Gitea #5).
+
+THIS IS THE CHART WHERE THE POLICY GETS GENUINELY TIGHT, and the reason is its
+probes: all three are exec probes. An exec probe runs inside the container
+through the kubelet's runtime and puts NO packet on the network, so there is no
+kubelet traffic to accommodate on any port - which means every port here can be
+restricted by source, with no probeSources needed at all. valkey is tight for
+the same reason.
+
+The one rule that cannot be fixed is the game port, and it depends on a value:
+
+  server.service.type == NodePort  players arrive from the internet, already
+                                   masqueraded, so the rule must be OPEN.
+  anything else (the default)      the only reachable path is in-cluster, i.e.
+                                   minecraft-router, so the rule is RESTRICTED
+                                   to this namespace plus allowedNamespaces -
+                                   and the router's namespace has to be in that
+                                   list.
+
+Both branches are rendered from the same value the Service reads, so they cannot
+disagree. The RCON and metrics ports are restricted in either case.
+
+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 }}
+{{- $allowedNs := $np.allowedNamespaces | default list }}
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
+  labels:
+    app: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
+spec:
+  {{- /*
+  Selects the StatefulSet's pods. ci/run-networkpolicy-test.sh fails if
+  this matches no pod spec of the same render - which is the mistake that
+  would otherwise leave a policy in the namespace filtering nothing, and
+  its usual cause is a label renamed in the workload template.
+  */}}
+  podSelector:
+    matchLabels:
+      app: {{ .Release.Name }}-{{ .Chart.Name }}-sfs
+  policyTypes:
+    - Ingress
+    {{- /*
+    Egress is listed because there is something real to restrict: a Minecraft
+    server needs DNS and HTTPS and nothing else in the normal case. Mod packs that
+    call out on other ports are the exception, and extraPorts is for them.
+    */}}
+    - Egress
+  ingress:
+    {{- if eq .Values.server.service.type "NodePort" }}
+    {{- /*
+    THE GAME PORT, NODEPORT BRANCH (server.service.type is NodePort). Open with no
+    "from": the senders are Minecraft clients on the internet and, after NodePort
+    masquerading, the source address is a cluster node anyway.
+
+    THE NUMBER IS THE POD PORT (server.port), not server.service.outwardPort. A
+    NetworkPolicy is evaluated after kube-proxy has translated the NodePort, so the
+    NodePort number would match nothing here while looking strict - and being the
+    only rule for the port, it would block every player instead.
+    */}}
+    - ports:
+        - protocol: TCP
+          port: {{ .Values.server.port | int64 }}
+    {{- end }}
+    {{- if not (eq .Values.server.service.type "NodePort") }}
+    {{- /*
+    THE GAME PORT, CLUSTER-INTERNAL BRANCH (the default): the Service is not a
+    NodePort, so nothing outside the cluster can reach this port through this
+    chart, and the rule is restricted to this namespace plus allowedNamespaces.
+
+    PUT THE ROUTER'S NAMESPACE IN allowedNamespaces. In this cluster players reach
+    the server through minecraft-router, which runs in its own namespace - so
+    without that entry the server is unreachable and the symptom is a connection
+    timeout in a game client, with a healthy pod behind it.
+    */}}
+    - ports:
+        - protocol: TCP
+          port: {{ .Values.server.port | int64 }}
+      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 }}
+        {{- range $allowedNs }}
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: {{ . | quote }}
+        {{- end }}
+    {{- end }}
+    {{- if .Values.server.rcon.enabled }}
+    {{- /*
+    RCON - remote console, i.e. full administrative control of the server. No
+    Service and no probe, so it is restricted to this namespace plus
+    allowedNamespaces: the rule with the most security value in this chart, and it
+    costs nothing.
+
+    GATED ON server.rcon.enabled, AND THAT GATE IS NOT COSMETIC. The containerPort
+    itself is rendered only when RCON is on (see the StatefulSet), so without the
+    same condition here the policy would name a port the pod does not declare -
+    which is not merely untidy: ci/run-networkpolicy-test.sh rejects it, and it
+    rejected exactly this while the chart was being written. A rule for a port
+    nothing listens on is a rule nobody can verify.
+    */}}
+    - ports:
+        - protocol: TCP
+          port: {{ .Values.server.rcon.port | int64 }}
+      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 }}
+        {{- range $allowedNs }}
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: {{ . | quote }}
+        {{- end }}
+    {{- end }}
+    {{- /*
+    The metrics port. No Service, no probe, so restricted like RCON. A Prometheus
+    that scrapes this release from another namespace needs that namespace in
+    allowedNamespaces - and the failure is a target that silently stops reporting,
+    which is worth knowing before it happens.
+    */}}
+    - ports:
+        - protocol: TCP
+          port: 19565
+      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 }}
+        {{- range $allowedNs }}
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: {{ . | quote }}
+        {{- 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
+    {{- /*
+    Outbound HTTPS. Needed for Mojang's session server when online-mode is on - a
+    server that cannot reach it rejects every login - and for resource-pack and mod
+    downloads. To any destination, because those are hostnames.
+    */}}
+    - 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 }}