Add a read-only Kubernetes source for zones, client groups and blocklists

The runtime can now take ClientGroup, BlockList and DNSZone objects
(fancydns.k6n.net/v1alpha1) from a cluster with -kube, from a pod's service
account or a kubeconfig alike. internal/kubesource watches them with dynamic
informers, converts and validates each object on its own, and publishes an
immutable snapshot. A bad object is skipped and keeps its last good version,
so one broken edit cannot remove a running policy; an invalid merged config is
dropped whole. The last snapshot is saved so a restart without apiserver access
still serves.

config.Store gains an overlay: Base() is what the YAML says, Get() is base plus
cluster objects. Everything that writes the config back (mutateConfig,
SetAdminAddr, the settings editor) now starts from Base(), otherwise cluster
objects would be copied into the file and shadow their own objects. YAML wins
every name collision. putACL and toggleBlocklist refuse to edit cluster-owned
objects. BlockList has no path field and refuses file:// URLs so a namespaced
object cannot pick files the runtime reads or writes. DNSZone is rendered
through the zone writer's own prove-by-reparse step, with the SOA serial taken
from metadata.generation so every replica renders identical bytes.

qlog: Flush reset the pending slice to [:0], so entries logged while it was
still storing the batch were appended over the same backing array. The race
detector found it through the new Kubernetes integration test. pending is now
set to nil, with a regression test that fails without the change.

CRD manifests, RBAC and examples are in deploy/k8s/crds; tests pin the schemas
to the Go spec structs so the two cannot drift.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

deploy/k8s/crds/crds.yaml

@@ -0,0 +1,124 @@
+# The fancy-dns custom resources. Cluster-scoped definitions, namespaced
+# objects. The runtime (`fancy-dns -kube`) watches them read-only.
+#
+# Field names are snake_case where they mirror config.yaml (allow_domains,
+# max_concurrent, ...), so a group copied out of the YAML pastes in unchanged.
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  name: dnszones.fancydns.k6n.net
+spec:
+  group: fancydns.k6n.net
+  scope: Namespaced
+  names: {kind: DNSZone, listKind: DNSZoneList, plural: dnszones, singular: dnszone, shortNames: [dnsz]}
+  versions:
+    - name: v1alpha1
+      served: true
+      storage: true
+      additionalPrinterColumns:
+        - {name: Zone, type: string, jsonPath: .spec.zone}
+        - {name: Age, type: date, jsonPath: .metadata.creationTimestamp}
+      schema:
+        openAPIV3Schema:
+          type: object
+          required: [spec]
+          properties:
+            spec:
+              type: object
+              required: [zone]
+              properties:
+                zone: {type: string, minLength: 3, maxLength: 253, description: "Zone apex, e.g. home.example.com"}
+                ttl: {type: integer, minimum: 1, maximum: 604800, description: "Zone $TTL and SOA minimum (seconds)"}
+                soa: {type: string, maxLength: 512, description: "SOA rdata; omit to synthesise one from the apex NS"}
+                records:
+                  type: array
+                  maxItems: 5000
+                  items:
+                    type: object
+                    required: [name, type, value]
+                    properties:
+                      name: {type: string, minLength: 1, maxLength: 253, description: "Owner; @ is the apex, a name without a trailing dot is relative to the zone"}
+                      type: {type: string, enum: [A, AAAA, CAA, CNAME, DHCID, HINFO, HTTPS, LOC, MX, NAPTR, NS, PTR, SRV, SPF, SSHFP, SVCB, TXT, URI]}
+                      ttl: {type: integer, minimum: 1, maximum: 604800}
+                      value: {type: string, minLength: 1, maxLength: 4096, description: "Presentation-format RDATA"}
+---
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  name: clientgroups.fancydns.k6n.net
+spec:
+  group: fancydns.k6n.net
+  scope: Namespaced
+  names: {kind: ClientGroup, listKind: ClientGroupList, plural: clientgroups, singular: clientgroup, shortNames: [cg]}
+  versions:
+    - name: v1alpha1
+      served: true
+      storage: true
+      additionalPrinterColumns:
+        - {name: Policy, type: string, jsonPath: .spec.policy}
+        - {name: Priority, type: integer, jsonPath: .spec.priority}
+        - {name: Age, type: date, jsonPath: .metadata.creationTimestamp}
+      schema:
+        openAPIV3Schema:
+          type: object
+          required: [spec]
+          properties:
+            spec:
+              type: object
+              required: [policy, match]
+              properties:
+                priority: {type: integer, default: 0, description: "Groups are first-match-wins; lower runs first, ties break on name. YAML groups always run before these."}
+                comment: {type: string, maxLength: 512}
+                policy: {type: string, enum: [allow, block_only, deny]}
+                match:
+                  type: object
+                  properties:
+                    cidrs: {type: array, items: {type: string}}
+                    ptr_suffixes: {type: array, items: {type: string}}
+                    tags: {type: array, items: {type: string}}
+                    any: {type: boolean}
+                allow_domains: {type: array, items: {type: string}}
+                deny_domains: {type: array, items: {type: string}}
+                skip_blocklist: {type: boolean}
+                skip_cache: {type: boolean}
+                rate_limit: {type: integer, minimum: 0}
+                max_concurrent: {type: integer, minimum: 0}
+                log_queries: {type: boolean}
+                upstreams: {type: array, items: {type: string}}
+---
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  name: blocklists.fancydns.k6n.net
+spec:
+  group: fancydns.k6n.net
+  scope: Namespaced
+  names: {kind: BlockList, listKind: BlockListList, plural: blocklists, singular: blocklist, shortNames: [bl]}
+  versions:
+    - name: v1alpha1
+      served: true
+      storage: true
+      additionalPrinterColumns:
+        - {name: URL, type: string, jsonPath: .spec.url}
+        - {name: Format, type: string, jsonPath: .spec.format}
+        - {name: Disabled, type: boolean, jsonPath: .spec.disabled}
+        - {name: Age, type: date, jsonPath: .metadata.creationTimestamp}
+      schema:
+        openAPIV3Schema:
+          type: object
+          required: [spec]
+          properties:
+            spec:
+              type: object
+              required: [url]
+              properties:
+                url: {type: string, pattern: '^https?://', description: "http(s) only; file paths are not accepted from the cluster"}
+                format: {type: string, enum: [auto, hosts, adblock, plain, rpz]}
+                mirror: {type: array, items: {type: string, pattern: '^https?://'}}
+                disabled: {type: boolean}
+                refresh: {type: string, description: "Go duration, e.g. 12h (default 24h)"}
+                timeout: {type: string, description: "Go duration, e.g. 30s"}
+                max_bytes: {type: integer, minimum: 1}
+                categories: {type: array, items: {type: string}}
+                comment: {type: string, maxLength: 512}
+                insecure_skip_tls_verify: {type: boolean}

deploy/k8s/crds/examples.yaml

@@ -0,0 +1,36 @@
+apiVersion: fancydns.k6n.net/v1alpha1
+kind: DNSZone
+metadata:
+  name: home
+  namespace: dns
+spec:
+  zone: home.example.com
+  ttl: 300
+  records:
+    - {name: "@", type: NS, value: ns1.home.example.com.}
+    - {name: ns1, type: A, value: 10.0.0.53}
+    - {name: nas, type: A, value: 10.0.0.20}
+    - {name: "*.apps", type: A, value: 10.0.0.30}
+---
+apiVersion: fancydns.k6n.net/v1alpha1
+kind: ClientGroup
+metadata:
+  name: kids
+  namespace: dns
+spec:
+  priority: 10
+  policy: block_only
+  match:
+    cidrs: [10.0.20.0/24]
+  deny_domains: ["**.tiktok.com"]
+---
+apiVersion: fancydns.k6n.net/v1alpha1
+kind: BlockList
+metadata:
+  name: stevenblack
+  namespace: dns
+spec:
+  url: https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts
+  format: hosts
+  refresh: 24h
+  categories: [ads, malware]

deploy/k8s/crds/kustomization.yaml

@@ -0,0 +1,8 @@
+# Apply the CRDs before anything that uses them:
+#   kubectl apply -f deploy/k8s/crds/crds.yaml
+#   kubectl apply -k deploy/k8s/crds        # RBAC for the runtime
+# examples.yaml is deliberately not included.
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - rbac.yaml

deploy/k8s/crds/rbac.yaml

@@ -0,0 +1,26 @@
+# Read-only access to the fancy-dns objects in one namespace, for the existing
+# `fancy-dns` service account. For a runtime outside the cluster, bind the same
+# Role (or a ClusterRole for -kube-namespace="") to the user in its kubeconfig.
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: fancy-dns-objects
+  namespace: dns
+rules:
+  - apiGroups: [fancydns.k6n.net]
+    resources: [dnszones, clientgroups, blocklists]
+    verbs: [get, list, watch]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: fancy-dns-objects
+  namespace: dns
+subjects:
+  - kind: ServiceAccount
+    name: fancy-dns
+    namespace: dns
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: Role
+  name: fancy-dns-objects