Replace Redis dependency with a generic cache store for fast path flag handling

management/internals/shared/grpc/fast_path_flag.go

@@ -3,27 +3,24 @@ package grpc
 import (
 	"context"
 	"errors"
-	"fmt"
-	"os"
 	"strings"
 	"sync/atomic"
 	"time"
 
-	"github.com/redis/go-redis/v9"
+	"github.com/eko/gocache/lib/v4/cache"
+	"github.com/eko/gocache/lib/v4/store"
 	log "github.com/sirupsen/logrus"
 )
 
 const (
-	fastPathRedisURLEnv = "NB_PEER_SYNC_REDIS_ADDRESS"
-
 	// DefaultFastPathFlagInterval is the default poll interval for the Sync
 	// fast-path feature flag. Kept lower than the log-level overrider because
 	// operators will want the toggle to propagate quickly during rollout.
 	DefaultFastPathFlagInterval = 1 * time.Minute
 
-	// DefaultFastPathRedisKey is the Redis key polled by RunFastPathFlagRoutine
+	// DefaultFastPathFlagKey is the cache key polled by RunFastPathFlagRoutine
 	// when the caller does not provide an override.
-	DefaultFastPathRedisKey = "peerSyncFastPath"
+	DefaultFastPathFlagKey = "peerSyncFastPath"
 )
 
 // FastPathFlag exposes the current on/off state of the Sync fast path. The
@@ -34,7 +31,7 @@ type FastPathFlag struct {
 }
 
 // NewFastPathFlag returns a FastPathFlag whose state is set to the given
-// value. Callers that need the runtime Redis-backed toggle should use
+// value. Callers that need the runtime toggle should use
 // RunFastPathFlagRoutine instead; this constructor is meant for tests and
 // for consumers that want to force the flag on or off.
 func NewFastPathFlag(enabled bool) *FastPathFlag {
@@ -60,50 +57,46 @@ func (f *FastPathFlag) setEnabled(v bool) {
 	f.enabled.Store(v)
 }
 
-// RunFastPathFlagRoutine starts a background goroutine that polls Redis for
-// the Sync fast-path feature flag and updates the returned FastPathFlag
-// accordingly. When NB_PEER_SYNC_REDIS_ADDRESS is not set the routine logs and
-// returns a handle that stays permanently disabled, so every Sync falls back
-// to the full network map path.
-func RunFastPathFlagRoutine(ctx context.Context, interval time.Duration, redisKey string) *FastPathFlag {
+// RunFastPathFlagRoutine starts a background goroutine that polls the shared
+// cache store for the Sync fast-path feature flag and updates the returned
+// FastPathFlag accordingly. When cacheStore is nil the routine returns a
+// handle that stays permanently disabled, so every Sync falls back to the
+// full network map path.
+//
+// The shared store is Redis-backed when NB_CACHE_REDIS_ADDRESS is set (so the
+// flag is toggled cluster-wide by writing the key in Redis) and falls back to
+// an in-process gocache otherwise, which is enough for single-replica dev and
+// test setups.
+func RunFastPathFlagRoutine(ctx context.Context, cacheStore store.StoreInterface, interval time.Duration, flagKey string) *FastPathFlag {
 	flag := &FastPathFlag{}
 
-	redisEnvAddr := os.Getenv(fastPathRedisURLEnv)
-	if redisEnvAddr == "" {
-		log.Infof("Environment variable %s not set. Sync fast path disabled", fastPathRedisURLEnv)
+	if cacheStore == nil {
+		log.Infof("Shared cache store not provided. Sync fast path disabled")
 		return flag
 	}
 
-	client, err := getFastPathRedisStore(ctx, redisEnvAddr)
-	if err != nil {
-		log.Errorf("Unable to connect to Redis at %v for Sync fast-path flag: %v", redisEnvAddr, err)
-		return flag
+	if flagKey == "" {
+		flagKey = DefaultFastPathFlagKey
 	}
 
-	if redisKey == "" {
-		redisKey = DefaultFastPathRedisKey
-	}
+	flagCache := cache.New[string](cacheStore)
 
 	go func() {
 		ticker := time.NewTicker(interval)
-		defer func() {
-			ticker.Stop()
-			if err := client.Close(); err != nil {
-				log.Debugf("close Sync fast-path redis client: %v", err)
-			}
-		}()
+		defer ticker.Stop()
 
 		refresh := func() {
 			getCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
 			defer cancel()
 
-			value, err := client.Get(getCtx, redisKey).Result()
-			if errors.Is(err, redis.Nil) {
-				flag.setEnabled(false)
-				return
-			}
+			value, err := flagCache.Get(getCtx, flagKey)
 			if err != nil {
-				log.Errorf("Unable to get Sync fast-path flag from redis at %v: %v", redisEnvAddr, err)
+				var notFound *store.NotFound
+				if errors.As(err, &notFound) {
+					flag.setEnabled(false)
+					return
+				}
+				log.Debugf("Sync fast-path flag refresh: %v", err)
 				return
 			}
 			flag.setEnabled(parseFastPathFlag(value))
@@ -126,8 +119,7 @@ func RunFastPathFlagRoutine(ctx context.Context, interval time.Duration, redisKe
 }
 
 // parseFastPathFlag accepts "1" or "true" (any casing, surrounding whitespace
-// tolerated) as enabled and treats every other value as disabled. Missing
-// keys surface as redis.Nil in the caller and also resolve to disabled.
+// tolerated) as enabled and treats every other value as disabled.
 func parseFastPathFlag(value string) bool {
 	v := strings.TrimSpace(value)
 	if v == "1" {
@@ -135,21 +127,3 @@ func parseFastPathFlag(value string) bool {
 	}
 	return strings.EqualFold(v, "true")
 }
-
-func getFastPathRedisStore(ctx context.Context, redisEnvAddr string) (*redis.Client, error) {
-	options, err := redis.ParseURL(redisEnvAddr)
-	if err != nil {
-		return nil, fmt.Errorf("parse redis fast-path url: %w", err)
-	}
-
-	client := redis.NewClient(options)
-	subCtx, cancel := context.WithTimeout(ctx, 2*time.Second)
-	defer cancel()
-
-	if _, err := client.Ping(subCtx).Result(); err != nil {
-		return nil, err
-	}
-
-	log.WithContext(subCtx).Infof("using redis for Sync fast-path flag at %s", redisEnvAddr)
-	return client, nil
-}