ipn/store/kubestore: cache state in memory

Fixes #7671

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/store/kubestore/store_kube.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"tailscale.com/ipn"
+	"tailscale.com/ipn/store/mem"
 	"tailscale.com/kube"
 	"tailscale.com/types/logger"
 )
@@ -19,6 +20,8 @@ import (
 type Store struct {
 	client     *kube.Client
 	secretName string
+
+	memory mem.Store
 }
 
 // New returns a new Store that persists to the named secret.
@@ -27,31 +30,37 @@ func New(_ logger.Logf, secretName string) (*Store, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Store{
+	s := &Store{
 		client:     c,
 		secretName: secretName,
-	}, nil
+	}
+	// Hydrate cache with the potentially current state
+	if err := s.loadState(); err != nil {
+		return nil, err
+	}
+	return s, nil
 }
 
-func (s *Store) String() string { return "kube.Store" }
+func (s *Store) loadState() error {
-
-// ReadState implements the StateStore interface.
-func (s *Store) ReadState(id ipn.StateKey) ([]byte, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 
 	secret, err := s.client.GetSecret(ctx, s.secretName)
 	if err != nil {
 		if st, ok := err.(*kube.Status); ok && st.Code == 404 {
-			return nil, ipn.ErrStateNotExist
+			return nil
 		}
-		return nil, err
+		return err
 	}
-	b, ok := secret.Data[sanitizeKey(id)]
+	s.memory.LoadFromMap(secret.Data)
-	if !ok {
+	return nil
-		return nil, ipn.ErrStateNotExist
 }
-	return b, nil
+
+func (s *Store) String() string { return "kube.Store" }
+
+// ReadState implements the StateStore interface.
+func (s *Store) ReadState(id ipn.StateKey) ([]byte, error) {
+	return s.memory.ReadState(ipn.StateKey(sanitizeKey(id)))
 }
 
 func sanitizeKey(k ipn.StateKey) string {
@@ -66,7 +75,12 @@ func sanitizeKey(k ipn.StateKey) string {
 }
 
 // WriteState implements the StateStore interface.
-func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
+func (s *Store) WriteState(id ipn.StateKey, bs []byte) (err error) {
+	defer func() {
+		if err == nil {
+			s.memory.WriteState(id, bs)
+		}
+	}()
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 

ipn/store/mem/store_mem.go

@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"sync"
 
+	"golang.org/x/exp/maps"
 	"tailscale.com/ipn"
 	"tailscale.com/types/logger"
 )
@@ -27,6 +28,7 @@ type Store struct {
 func (s *Store) String() string { return "mem.Store" }
 
 // ReadState implements the StateStore interface.
+// It returns ipn.ErrStateNotExist if the state does not exist.
 func (s *Store) ReadState(id ipn.StateKey) ([]byte, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -38,6 +40,7 @@ func (s *Store) ReadState(id ipn.StateKey) ([]byte, error) {
 }
 
 // WriteState implements the StateStore interface.
+// It never returns an error.
 func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -48,6 +51,19 @@ func (s *Store) WriteState(id ipn.StateKey, bs []byte) error {
 	return nil
 }
 
+// LoadFromMap loads the in-memory cache from the provided map.
+// Any existing content is cleared, and the provided map is
+// copied into the cache.
+func (s *Store) LoadFromMap(m map[string][]byte) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	maps.Clear(s.cache)
+	for k, v := range m {
+		s.cache[ipn.StateKey(k)] = v
+	}
+	return
+}
+
 // LoadFromJSON attempts to unmarshal json content into the
 // in-memory cache.
 func (s *Store) LoadFromJSON(data []byte) error {