cmd/k8s-operator,k8s-operator/api-proxy: move k8s proxy code to library (#15857)

The defaultEnv and defaultBool functions are copied over temporarily
to minimise diff. This lays the ground work for having both the operator
and the new k8s-proxy binary implement the API proxy

Updates #13358

Change-Id: Ieacc79af64df2f13b27a18135517bb31c80a5a02
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>

k8s-operator/api-proxy/doc.go

@@ -0,0 +1,8 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !plan9
+
+// Package apiproxy contains the Kubernetes API Proxy implementation used by
+// k8s-operator and k8s-proxy.
+package apiproxy

k8s-operator/api-proxy/env.go

@@ -0,0 +1,29 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !plan9
+
+package apiproxy
+
+import (
+	"os"
+
+	"tailscale.com/types/opt"
+)
+
+func defaultBool(envName string, defVal bool) bool {
+	vs := os.Getenv(envName)
+	if vs == "" {
+		return defVal
+	}
+	v, _ := opt.Bool(vs).Get()
+	return v
+}
+
+func defaultEnv(envName, defVal string) string {
+	v := os.Getenv(envName)
+	if v == "" {
+		return defVal
+	}
+	return v
+}

k8s-operator/api-proxy/proxy.go

@@ -0,0 +1,421 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !plan9
+
+package apiproxy
+
+import (
+	"crypto/tls"
+	"fmt"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/netip"
+	"net/url"
+	"os"
+	"strings"
+
+	"github.com/pkg/errors"
+	"go.uber.org/zap"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/transport"
+	"tailscale.com/client/local"
+	"tailscale.com/client/tailscale/apitype"
+	ksr "tailscale.com/k8s-operator/sessionrecording"
+	"tailscale.com/kube/kubetypes"
+	"tailscale.com/tailcfg"
+	"tailscale.com/tsnet"
+	"tailscale.com/util/clientmetric"
+	"tailscale.com/util/ctxkey"
+	"tailscale.com/util/set"
+)
+
+var (
+	// counterNumRequestsproxies counts the number of API server requests proxied via this proxy.
+	counterNumRequestsProxied = clientmetric.NewCounter("k8s_auth_proxy_requests_proxied")
+	whoIsKey                  = ctxkey.New("", (*apitype.WhoIsResponse)(nil))
+)
+
+type APIServerProxyMode int
+
+func (a APIServerProxyMode) String() string {
+	switch a {
+	case APIServerProxyModeDisabled:
+		return "disabled"
+	case APIServerProxyModeEnabled:
+		return "auth"
+	case APIServerProxyModeNoAuth:
+		return "noauth"
+	default:
+		return "unknown"
+	}
+}
+
+const (
+	APIServerProxyModeDisabled APIServerProxyMode = iota
+	APIServerProxyModeEnabled
+	APIServerProxyModeNoAuth
+)
+
+func ParseAPIProxyMode() APIServerProxyMode {
+	haveAuthProxyEnv := os.Getenv("AUTH_PROXY") != ""
+	haveAPIProxyEnv := os.Getenv("APISERVER_PROXY") != ""
+	switch {
+	case haveAPIProxyEnv && haveAuthProxyEnv:
+		log.Fatal("AUTH_PROXY and APISERVER_PROXY are mutually exclusive")
+	case haveAuthProxyEnv:
+		var authProxyEnv = defaultBool("AUTH_PROXY", false) // deprecated
+		if authProxyEnv {
+			return APIServerProxyModeEnabled
+		}
+		return APIServerProxyModeDisabled
+	case haveAPIProxyEnv:
+		var apiProxyEnv = defaultEnv("APISERVER_PROXY", "") // true, false or "noauth"
+		switch apiProxyEnv {
+		case "true":
+			return APIServerProxyModeEnabled
+		case "false", "":
+			return APIServerProxyModeDisabled
+		case "noauth":
+			return APIServerProxyModeNoAuth
+		default:
+			panic(fmt.Sprintf("unknown APISERVER_PROXY value %q", apiProxyEnv))
+		}
+	}
+	return APIServerProxyModeDisabled
+}
+
+// maybeLaunchAPIServerProxy launches the auth proxy, which is a small HTTP server
+// that authenticates requests using the Tailscale LocalAPI and then proxies
+// them to the kube-apiserver.
+func MaybeLaunchAPIServerProxy(zlog *zap.SugaredLogger, restConfig *rest.Config, s *tsnet.Server, mode APIServerProxyMode) {
+	if mode == APIServerProxyModeDisabled {
+		return
+	}
+	startlog := zlog.Named("launchAPIProxy")
+	if mode == APIServerProxyModeNoAuth {
+		restConfig = rest.AnonymousClientConfig(restConfig)
+	}
+	cfg, err := restConfig.TransportConfig()
+	if err != nil {
+		startlog.Fatalf("could not get rest.TransportConfig(): %v", err)
+	}
+
+	// Kubernetes uses SPDY for exec and port-forward, however SPDY is
+	// incompatible with HTTP/2; so disable HTTP/2 in the proxy.
+	tr := http.DefaultTransport.(*http.Transport).Clone()
+	tr.TLSClientConfig, err = transport.TLSConfigFor(cfg)
+	if err != nil {
+		startlog.Fatalf("could not get transport.TLSConfigFor(): %v", err)
+	}
+	tr.TLSNextProto = make(map[string]func(authority string, c *tls.Conn) http.RoundTripper)
+
+	rt, err := transport.HTTPWrappersForConfig(cfg, tr)
+	if err != nil {
+		startlog.Fatalf("could not get rest.TransportConfig(): %v", err)
+	}
+	go runAPIServerProxy(s, rt, zlog.Named("apiserver-proxy"), mode, restConfig.Host)
+}
+
+// runAPIServerProxy runs an HTTP server that authenticates requests using the
+// Tailscale LocalAPI and then proxies them to the Kubernetes API.
+// It listens on :443 and uses the Tailscale HTTPS certificate.
+// s will be started if it is not already running.
+// rt is used to proxy requests to the Kubernetes API.
+//
+// mode controls how the proxy behaves:
+//   - apiserverProxyModeDisabled: the proxy is not started.
+//   - apiserverProxyModeEnabled: the proxy is started and requests are impersonated using the
+//     caller's identity from the Tailscale LocalAPI.
+//   - apiserverProxyModeNoAuth: the proxy is started and requests are not impersonated and
+//     are passed through to the Kubernetes API.
+//
+// It never returns.
+func runAPIServerProxy(ts *tsnet.Server, rt http.RoundTripper, log *zap.SugaredLogger, mode APIServerProxyMode, host string) {
+	if mode == APIServerProxyModeDisabled {
+		return
+	}
+	ln, err := ts.Listen("tcp", ":443")
+	if err != nil {
+		log.Fatalf("could not listen on :443: %v", err)
+	}
+	u, err := url.Parse(host)
+	if err != nil {
+		log.Fatalf("runAPIServerProxy: failed to parse URL %v", err)
+	}
+
+	lc, err := ts.LocalClient()
+	if err != nil {
+		log.Fatalf("could not get local client: %v", err)
+	}
+
+	ap := &apiserverProxy{
+		log:         log,
+		lc:          lc,
+		mode:        mode,
+		upstreamURL: u,
+		ts:          ts,
+	}
+	ap.rp = &httputil.ReverseProxy{
+		Rewrite: func(pr *httputil.ProxyRequest) {
+			ap.addImpersonationHeadersAsRequired(pr.Out)
+		},
+		Transport: rt,
+	}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", ap.serveDefault)
+	mux.HandleFunc("POST /api/v1/namespaces/{namespace}/pods/{pod}/exec", ap.serveExecSPDY)
+	mux.HandleFunc("GET /api/v1/namespaces/{namespace}/pods/{pod}/exec", ap.serveExecWS)
+
+	hs := &http.Server{
+		// Kubernetes uses SPDY for exec and port-forward, however SPDY is
+		// incompatible with HTTP/2; so disable HTTP/2 in the proxy.
+		TLSConfig: &tls.Config{
+			GetCertificate: lc.GetCertificate,
+			NextProtos:     []string{"http/1.1"},
+		},
+		TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
+		Handler:      mux,
+	}
+	log.Infof("API server proxy in %q mode is listening on %s", mode, ln.Addr())
+	if err := hs.ServeTLS(ln, "", ""); err != nil {
+		log.Fatalf("runAPIServerProxy: failed to serve %v", err)
+	}
+}
+
+// apiserverProxy is an [net/http.Handler] that authenticates requests using the Tailscale
+// LocalAPI and then proxies them to the Kubernetes API.
+type apiserverProxy struct {
+	log *zap.SugaredLogger
+	lc  *local.Client
+	rp  *httputil.ReverseProxy
+
+	mode        APIServerProxyMode
+	ts          *tsnet.Server
+	upstreamURL *url.URL
+}
+
+// serveDefault is the default handler for Kubernetes API server requests.
+func (ap *apiserverProxy) serveDefault(w http.ResponseWriter, r *http.Request) {
+	who, err := ap.whoIs(r)
+	if err != nil {
+		ap.authError(w, err)
+		return
+	}
+	counterNumRequestsProxied.Add(1)
+	ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
+}
+
+// serveExecSPDY serves 'kubectl exec' requests for sessions streamed over SPDY,
+// optionally configuring the kubectl exec sessions to be recorded.
+func (ap *apiserverProxy) serveExecSPDY(w http.ResponseWriter, r *http.Request) {
+	ap.execForProto(w, r, ksr.SPDYProtocol)
+}
+
+// serveExecWS serves 'kubectl exec' requests for sessions streamed over WebSocket,
+// optionally configuring the kubectl exec sessions to be recorded.
+func (ap *apiserverProxy) serveExecWS(w http.ResponseWriter, r *http.Request) {
+	ap.execForProto(w, r, ksr.WSProtocol)
+}
+
+func (ap *apiserverProxy) execForProto(w http.ResponseWriter, r *http.Request, proto ksr.Protocol) {
+	const (
+		podNameKey       = "pod"
+		namespaceNameKey = "namespace"
+		upgradeHeaderKey = "Upgrade"
+	)
+
+	who, err := ap.whoIs(r)
+	if err != nil {
+		ap.authError(w, err)
+		return
+	}
+	counterNumRequestsProxied.Add(1)
+	failOpen, addrs, err := determineRecorderConfig(who)
+	if err != nil {
+		ap.log.Errorf("error trying to determine whether the 'kubectl exec' session needs to be recorded: %v", err)
+		return
+	}
+	if failOpen && len(addrs) == 0 { // will not record
+		ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
+		return
+	}
+	ksr.CounterSessionRecordingsAttempted.Add(1) // at this point we know that users intended for this session to be recorded
+	if !failOpen && len(addrs) == 0 {
+		msg := "forbidden: 'kubectl exec' session must be recorded, but no recorders are available."
+		ap.log.Error(msg)
+		http.Error(w, msg, http.StatusForbidden)
+		return
+	}
+
+	wantsHeader := upgradeHeaderForProto[proto]
+	if h := r.Header.Get(upgradeHeaderKey); h != wantsHeader {
+		msg := fmt.Sprintf("[unexpected] unable to verify that streaming protocol is %s, wants Upgrade header %q, got: %q", proto, wantsHeader, h)
+		if failOpen {
+			msg = msg + "; failure mode is 'fail open'; continuing session without recording."
+			ap.log.Warn(msg)
+			ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
+			return
+		}
+		ap.log.Error(msg)
+		msg += "; failure mode is 'fail closed'; closing connection."
+		http.Error(w, msg, http.StatusForbidden)
+		return
+	}
+
+	opts := ksr.HijackerOpts{
+		Req:       r,
+		W:         w,
+		Proto:     proto,
+		TS:        ap.ts,
+		Who:       who,
+		Addrs:     addrs,
+		FailOpen:  failOpen,
+		Pod:       r.PathValue(podNameKey),
+		Namespace: r.PathValue(namespaceNameKey),
+		Log:       ap.log,
+	}
+	h := ksr.New(opts)
+
+	ap.rp.ServeHTTP(h, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
+}
+
+func (h *apiserverProxy) addImpersonationHeadersAsRequired(r *http.Request) {
+	r.URL.Scheme = h.upstreamURL.Scheme
+	r.URL.Host = h.upstreamURL.Host
+	if h.mode == APIServerProxyModeNoAuth {
+		// If we are not providing authentication, then we are just
+		// proxying to the Kubernetes API, so we don't need to do
+		// anything else.
+		return
+	}
+
+	// We want to proxy to the Kubernetes API, but we want to use
+	// the caller's identity to do so. We do this by impersonating
+	// the caller using the Kubernetes User Impersonation feature:
+	// https://kubernetes.io/docs/reference/access-authn-authz/authentication/#user-impersonation
+
+	// Out of paranoia, remove all authentication headers that might
+	// have been set by the client.
+	r.Header.Del("Authorization")
+	r.Header.Del("Impersonate-Group")
+	r.Header.Del("Impersonate-User")
+	r.Header.Del("Impersonate-Uid")
+	for k := range r.Header {
+		if strings.HasPrefix(k, "Impersonate-Extra-") {
+			r.Header.Del(k)
+		}
+	}
+
+	// Now add the impersonation headers that we want.
+	if err := addImpersonationHeaders(r, h.log); err != nil {
+		log.Print("failed to add impersonation headers: ", err.Error())
+	}
+}
+
+func (ap *apiserverProxy) whoIs(r *http.Request) (*apitype.WhoIsResponse, error) {
+	return ap.lc.WhoIs(r.Context(), r.RemoteAddr)
+}
+
+func (ap *apiserverProxy) authError(w http.ResponseWriter, err error) {
+	ap.log.Errorf("failed to authenticate caller: %v", err)
+	http.Error(w, "failed to authenticate caller", http.StatusInternalServerError)
+}
+
+const (
+	// oldCapabilityName is a legacy form of
+	// tailfcg.PeerCapabilityKubernetes capability. The only capability rule
+	// that is respected for this form is group impersonation - for
+	// backwards compatibility reasons.
+	// TODO (irbekrm): determine if anyone uses this and remove if possible.
+	oldCapabilityName = "https://" + tailcfg.PeerCapabilityKubernetes
+)
+
+// addImpersonationHeaders adds the appropriate headers to r to impersonate the
+// caller when proxying to the Kubernetes API. It uses the WhoIsResponse stashed
+// in the context by the apiserverProxy.
+func addImpersonationHeaders(r *http.Request, log *zap.SugaredLogger) error {
+	log = log.With("remote", r.RemoteAddr)
+	who := whoIsKey.Value(r.Context())
+	rules, err := tailcfg.UnmarshalCapJSON[kubetypes.KubernetesCapRule](who.CapMap, tailcfg.PeerCapabilityKubernetes)
+	if len(rules) == 0 && err == nil {
+		// Try the old capability name for backwards compatibility.
+		rules, err = tailcfg.UnmarshalCapJSON[kubetypes.KubernetesCapRule](who.CapMap, oldCapabilityName)
+	}
+	if err != nil {
+		return fmt.Errorf("failed to unmarshal capability: %v", err)
+	}
+
+	var groupsAdded set.Slice[string]
+	for _, rule := range rules {
+		if rule.Impersonate == nil {
+			continue
+		}
+		for _, group := range rule.Impersonate.Groups {
+			if groupsAdded.Contains(group) {
+				continue
+			}
+			r.Header.Add("Impersonate-Group", group)
+			groupsAdded.Add(group)
+			log.Debugf("adding group impersonation header for user group %s", group)
+		}
+	}
+
+	if !who.Node.IsTagged() {
+		r.Header.Set("Impersonate-User", who.UserProfile.LoginName)
+		log.Debugf("adding user impersonation header for user %s", who.UserProfile.LoginName)
+		return nil
+	}
+	// "Impersonate-Group" requires "Impersonate-User" to be set, so we set it
+	// to the node FQDN for tagged nodes.
+	nodeName := strings.TrimSuffix(who.Node.Name, ".")
+	r.Header.Set("Impersonate-User", nodeName)
+	log.Debugf("adding user impersonation header for node name %s", nodeName)
+
+	// For legacy behavior (before caps), set the groups to the nodes tags.
+	if groupsAdded.Slice().Len() == 0 {
+		for _, tag := range who.Node.Tags {
+			r.Header.Add("Impersonate-Group", tag)
+			log.Debugf("adding group impersonation header for node tag %s", tag)
+		}
+	}
+	return nil
+}
+
+// determineRecorderConfig determines recorder config from requester's peer
+// capabilities. Determines whether a 'kubectl exec' session from this requester
+// needs to be recorded and what recorders the recording should be sent to.
+func determineRecorderConfig(who *apitype.WhoIsResponse) (failOpen bool, recorderAddresses []netip.AddrPort, _ error) {
+	if who == nil {
+		return false, nil, errors.New("[unexpected] cannot determine caller")
+	}
+	failOpen = true
+	rules, err := tailcfg.UnmarshalCapJSON[kubetypes.KubernetesCapRule](who.CapMap, tailcfg.PeerCapabilityKubernetes)
+	if err != nil {
+		return failOpen, nil, fmt.Errorf("failed to unmarshal Kubernetes capability: %w", err)
+	}
+	if len(rules) == 0 {
+		return failOpen, nil, nil
+	}
+
+	for _, rule := range rules {
+		if len(rule.RecorderAddrs) != 0 {
+			// TODO (irbekrm): here or later determine if the
+			// recorders behind those addrs are online - else we
+			// spend 30s trying to reach a recorder whose tailscale
+			// status is offline.
+			recorderAddresses = append(recorderAddresses, rule.RecorderAddrs...)
+		}
+		if rule.EnforceRecorder {
+			failOpen = false
+		}
+	}
+	return failOpen, recorderAddresses, nil
+}
+
+var upgradeHeaderForProto = map[ksr.Protocol]string{
+	ksr.SPDYProtocol: "SPDY/3.1",
+	ksr.WSProtocol:   "websocket",
+}

k8s-operator/api-proxy/proxy_test.go

@@ -0,0 +1,199 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !plan9
+
+package apiproxy
+
+import (
+	"net/http"
+	"net/netip"
+	"reflect"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"go.uber.org/zap"
+	"tailscale.com/client/tailscale/apitype"
+	"tailscale.com/tailcfg"
+	"tailscale.com/util/must"
+)
+
+func TestImpersonationHeaders(t *testing.T) {
+	zl, err := zap.NewDevelopment()
+	if err != nil {
+		t.Fatal(err)
+	}
+	tests := []struct {
+		name     string
+		emailish string
+		tags     []string
+		capMap   tailcfg.PeerCapMap
+
+		wantHeaders http.Header
+	}{
+		{
+			name:     "user",
+			emailish: "foo@example.com",
+			wantHeaders: http.Header{
+				"Impersonate-User": {"foo@example.com"},
+			},
+		},
+		{
+			name:     "tagged",
+			emailish: "tagged-device",
+			tags:     []string{"tag:foo", "tag:bar"},
+			wantHeaders: http.Header{
+				"Impersonate-User":  {"node.ts.net"},
+				"Impersonate-Group": {"tag:foo", "tag:bar"},
+			},
+		},
+		{
+			name:     "user-with-cap",
+			emailish: "foo@example.com",
+			capMap: tailcfg.PeerCapMap{
+				tailcfg.PeerCapabilityKubernetes: {
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group1","group2"]}}`),
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group1","group3"]}}`), // One group is duplicated.
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group4"]}}`),
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group2"]}}`), // duplicate
+
+					// These should be ignored, but should parse correctly.
+					tailcfg.RawMessage(`{}`),
+					tailcfg.RawMessage(`{"impersonate":{}}`),
+					tailcfg.RawMessage(`{"impersonate":{"groups":[]}}`),
+				},
+			},
+			wantHeaders: http.Header{
+				"Impersonate-Group": {"group1", "group2", "group3", "group4"},
+				"Impersonate-User":  {"foo@example.com"},
+			},
+		},
+		{
+			name:     "tagged-with-cap",
+			emailish: "tagged-device",
+			tags:     []string{"tag:foo", "tag:bar"},
+			capMap: tailcfg.PeerCapMap{
+				tailcfg.PeerCapabilityKubernetes: {
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group1"]}}`),
+				},
+			},
+			wantHeaders: http.Header{
+				"Impersonate-Group": {"group1"},
+				"Impersonate-User":  {"node.ts.net"},
+			},
+		},
+		{
+			name:     "mix-of-caps",
+			emailish: "tagged-device",
+			tags:     []string{"tag:foo", "tag:bar"},
+			capMap: tailcfg.PeerCapMap{
+				tailcfg.PeerCapabilityKubernetes: {
+					tailcfg.RawMessage(`{"impersonate":{"groups":["group1"]},"recorder":["tag:foo"],"enforceRecorder":true}`),
+				},
+			},
+			wantHeaders: http.Header{
+				"Impersonate-Group": {"group1"},
+				"Impersonate-User":  {"node.ts.net"},
+			},
+		},
+		{
+			name:     "bad-cap",
+			emailish: "tagged-device",
+			tags:     []string{"tag:foo", "tag:bar"},
+			capMap: tailcfg.PeerCapMap{
+				tailcfg.PeerCapabilityKubernetes: {
+					tailcfg.RawMessage(`[]`),
+				},
+			},
+			wantHeaders: http.Header{},
+		},
+	}
+
+	for _, tc := range tests {
+		r := must.Get(http.NewRequest("GET", "https://op.ts.net/api/foo", nil))
+		r = r.WithContext(whoIsKey.WithValue(r.Context(), &apitype.WhoIsResponse{
+			Node: &tailcfg.Node{
+				Name: "node.ts.net",
+				Tags: tc.tags,
+			},
+			UserProfile: &tailcfg.UserProfile{
+				LoginName: tc.emailish,
+			},
+			CapMap: tc.capMap,
+		}))
+		addImpersonationHeaders(r, zl.Sugar())
+
+		if d := cmp.Diff(tc.wantHeaders, r.Header); d != "" {
+			t.Errorf("unexpected header (-want +got):\n%s", d)
+		}
+	}
+}
+
+func Test_determineRecorderConfig(t *testing.T) {
+	addr1, addr2 := netip.MustParseAddrPort("[fd7a:115c:a1e0:ab12:4843:cd96:626b:628b]:80"), netip.MustParseAddrPort("100.99.99.99:80")
+	tests := []struct {
+		name                  string
+		wantFailOpen          bool
+		wantRecorderAddresses []netip.AddrPort
+		who                   *apitype.WhoIsResponse
+	}{
+		{
+			name:                  "two_ips_fail_closed",
+			who:                   whoResp(map[string][]string{string(tailcfg.PeerCapabilityKubernetes): {`{"recorderAddrs":["[fd7a:115c:a1e0:ab12:4843:cd96:626b:628b]:80","100.99.99.99:80"],"enforceRecorder":true}`}}),
+			wantRecorderAddresses: []netip.AddrPort{addr1, addr2},
+		},
+		{
+			name:                  "two_ips_fail_open",
+			who:                   whoResp(map[string][]string{string(tailcfg.PeerCapabilityKubernetes): {`{"recorderAddrs":["[fd7a:115c:a1e0:ab12:4843:cd96:626b:628b]:80","100.99.99.99:80"]}`}}),
+			wantRecorderAddresses: []netip.AddrPort{addr1, addr2},
+			wantFailOpen:          true,
+		},
+		{
+			name:                  "odd_rule_combination_fail_closed",
+			who:                   whoResp(map[string][]string{string(tailcfg.PeerCapabilityKubernetes): {`{"recorderAddrs":["100.99.99.99:80"],"enforceRecorder":false}`, `{"recorderAddrs":["[fd7a:115c:a1e0:ab12:4843:cd96:626b:628b]:80"]}`, `{"enforceRecorder":true,"impersonate":{"groups":["system:masters"]}}`}}),
+			wantRecorderAddresses: []netip.AddrPort{addr2, addr1},
+		},
+		{
+			name:         "no_caps",
+			who:          whoResp(map[string][]string{}),
+			wantFailOpen: true,
+		},
+		{
+			name:         "no_recorder_caps",
+			who:          whoResp(map[string][]string{"foo": {`{"x":"y"}`}, string(tailcfg.PeerCapabilityKubernetes): {`{"impersonate":{"groups":["system:masters"]}}`}}),
+			wantFailOpen: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotFailOpen, gotRecorderAddresses, err := determineRecorderConfig(tt.who)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if gotFailOpen != tt.wantFailOpen {
+				t.Errorf("determineRecorderConfig() gotFailOpen = %v, want %v", gotFailOpen, tt.wantFailOpen)
+			}
+			if !reflect.DeepEqual(gotRecorderAddresses, tt.wantRecorderAddresses) {
+				t.Errorf("determineRecorderConfig() gotRecorderAddresses = %v, want %v", gotRecorderAddresses, tt.wantRecorderAddresses)
+			}
+		})
+	}
+}
+
+func whoResp(capMap map[string][]string) *apitype.WhoIsResponse {
+	resp := &apitype.WhoIsResponse{
+		CapMap: tailcfg.PeerCapMap{},
+	}
+	for cap, rules := range capMap {
+		resp.CapMap[tailcfg.PeerCapability(cap)] = raw(rules...)
+	}
+	return resp
+}
+
+func raw(in ...string) []tailcfg.RawMessage {
+	var out []tailcfg.RawMessage
+	for _, i := range in {
+		out = append(out, tailcfg.RawMessage(i))
+	}
+	return out
+}