Split the console from the resolver: fancy-dns-console writes the cluster

fancy-dns-console is a second binary holding the web UI, authentication and
every edit. It writes ClientGroup, BlockList and DNSZone objects through the new
kubeedit package and forwards all other /api routes to a running resolver
with its own key, dropping the browser's credentials, so it can run in the
cluster or on a workstation with a kubeconfig and nothing about the resolver's
placement matters. The resolver never imports kubeedit and the console is not on
the DNS path.

kubeedit validates every spec with the runtime's own converters
(kubesource.CheckGroup/CheckList/CheckZone) before writing, so the console
cannot store an object the resolver would reject. Zone edits keep the
file-based writer's behaviour: duplicate and below-a-delegation records are
refused, a delegation in a new zone also gives the zone its servers, and a
zone with no apex NS is never stored. Each object records the editing user in
an annotation; updates retry on conflict.

The resolver reports groups from ClientGroup objects as source "kubernetes" and
counter-only rows (the "(default)" bucket, or a group removed since) as
"history", and lists DNSZone zones as the editable ones. The console uses that
to leave the YAML's groups alone and to drop history rows, which the UI would
otherwise send back on save. Its GET /api/clients overlays the cluster's
current objects on the resolver's list, because the resolver only sees an edit
after its watch fires and a save made just after another would delete the
first.

An end-to-end test runs both halves against one fake apiserver: a group saved
through the console refuses queries, a zone built record by record answers
authoritatively, and a request with the resolver's own key is rejected by the
console.

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

cmd/fancy-dns-console/main.go

@@ -0,0 +1,138 @@
+// Command fancy-dns-console is the editing half of fancy-dns: the web UI and
+// the API behind it, writing ClientGroup, BlockList and DNSZone objects to
+// Kubernetes and forwarding everything else to a running resolver.
+//
+// It can run in the cluster or on a workstation (with a kubeconfig); the
+// resolver it manages need not be in the same place.
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"log/slog"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+	"time"
+
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/app"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/config"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/console"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/kubeedit"
+	"git.k8s-git-k6n.net/mats/fancy-dns/internal/kubesource"
+)
+
+func main() {
+	var (
+		configPath  = flag.String("config", envOr("FANCYDNS_CONSOLE_CONFIG", "/etc/fancy-dns/console.yaml"), "console configuration (api: listen, auth, ui)")
+		runtimeURL  = flag.String("runtime-url", os.Getenv("FANCYDNS_RUNTIME_URL"), "admin API of the resolver, e.g. http://fancy-dns.dns:9053")
+		kubeconfig  = flag.String("kubeconfig", os.Getenv("FANCYDNS_KUBECONFIG"), "kubeconfig (default: in-cluster service account, then $KUBECONFIG, then ~/.kube/config)")
+		kubeContext = flag.String("kube-context", os.Getenv("FANCYDNS_KUBE_CONTEXT"), "kubeconfig context")
+		kubeNS      = flag.String("kube-namespace", os.Getenv("FANCYDNS_KUBE_NAMESPACE"), "namespace the objects live in (default: the pod's own)")
+		showVersion = flag.Bool("version", false, "print the version and exit")
+		checkOnly   = flag.Bool("check", false, "validate the configuration and exit")
+	)
+	flag.Parse()
+	if *showVersion {
+		fmt.Println("fancy-dns-console", app.Version)
+		return
+	}
+	if err := run(*configPath, *runtimeURL, *kubeconfig, *kubeContext, *kubeNS, *checkOnly); err != nil {
+		fmt.Fprintln(os.Stderr, "fancy-dns-console:", err)
+		os.Exit(1)
+	}
+}
+
+func run(configPath, runtimeURL, kubeconfig, kubeContext, ns string, checkOnly bool) error {
+	cfg, err := config.Load(configPath)
+	if err != nil {
+		if strings.Contains(err.Error(), "blocklist is enabled") {
+			err = fmt.Errorf("%w (the console has no blocklists of its own: put \"blocklist: {enabled: false}\" in its config)", err)
+		}
+		return err
+	}
+	if runtimeURL == "" {
+		return errors.New("-runtime-url (or FANCYDNS_RUNTIME_URL) is required")
+	}
+	rt, err := console.NewRuntime(runtimeURL, os.Getenv("FANCYDNS_RUNTIME_KEY"))
+	if err != nil {
+		return err
+	}
+	if ns == "" {
+		ns = kubesource.Namespace()
+	}
+	if ns == "" {
+		return errors.New("-kube-namespace is required when not running in a pod")
+	}
+	client, from, err := kubesource.NewClient(kubesource.ClientOptions{Kubeconfig: kubeconfig, Context: kubeContext})
+	if err != nil {
+		return err
+	}
+
+	level := slog.LevelInfo
+	if cfg.Log.Level == "debug" {
+		level = slog.LevelDebug
+	}
+	log := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: level})).With("service", "fancy-dns-console", "version", app.Version)
+
+	c, err := console.New(console.Options{
+		Config:  config.NewStore(cfg, configPath),
+		Runtime: rt,
+		Editor:  kubeedit.New(client, ns),
+		Logger:  log,
+		Version: app.Version,
+	})
+	if err != nil {
+		return err
+	}
+	handler, err := c.Handler()
+	if err != nil {
+		return err
+	}
+	if checkOnly {
+		fmt.Println("configuration is valid:", configPath)
+		return nil
+	}
+	if len(cfg.API.TLSListen) > 0 {
+		log.Warn("api.tls_listen is ignored by the console; terminate TLS at an ingress or proxy")
+	}
+	if len(cfg.API.Listen) == 0 {
+		return errors.New("api.listen is empty: nowhere to serve the console")
+	}
+
+	srv := &http.Server{Handler: handler, ReadHeaderTimeout: 15 * time.Second, IdleTimeout: 120 * time.Second}
+	errc := make(chan error, len(cfg.API.Listen))
+	for _, addr := range cfg.API.Listen {
+		ln, err := net.Listen("tcp", addr)
+		if err != nil {
+			return fmt.Errorf("bind %s: %w", addr, err)
+		}
+		log.Info("console listening", "addr", ln.Addr().String(), "namespace", ns, "kubernetes", from, "resolver", runtimeURL)
+		go func() { errc <- srv.Serve(ln) }()
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+	select {
+	case <-ctx.Done():
+	case err := <-errc:
+		if !errors.Is(err, http.ErrServerClosed) {
+			return err
+		}
+	}
+	sctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	return srv.Shutdown(sctx)
+}
+
+func envOr(key, def string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return def
+}