init repo

vendor/github.com/redis/go-redis/v9/sentinel.go

@@ -0,0 +1,841 @@
+package redis
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"net"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/redis/go-redis/v9/internal"
+	"github.com/redis/go-redis/v9/internal/pool"
+	"github.com/redis/go-redis/v9/internal/rand"
+)
+
+//------------------------------------------------------------------------------
+
+// FailoverOptions are used to configure a failover client and should
+// be passed to NewFailoverClient.
+type FailoverOptions struct {
+	// The master name.
+	MasterName string
+	// A seed list of host:port addresses of sentinel nodes.
+	SentinelAddrs []string
+
+	// ClientName will execute the `CLIENT SETNAME ClientName` command for each conn.
+	ClientName string
+
+	// If specified with SentinelPassword, enables ACL-based authentication (via
+	// AUTH <user> <pass>).
+	SentinelUsername string
+	// Sentinel password from "requirepass <password>" (if enabled) in Sentinel
+	// configuration, or, if SentinelUsername is also supplied, used for ACL-based
+	// authentication.
+	SentinelPassword string
+
+	// Allows routing read-only commands to the closest master or replica node.
+	// This option only works with NewFailoverClusterClient.
+	RouteByLatency bool
+	// Allows routing read-only commands to the random master or replica node.
+	// This option only works with NewFailoverClusterClient.
+	RouteRandomly bool
+
+	// Route all commands to replica read-only nodes.
+	ReplicaOnly bool
+
+	// Use replicas disconnected with master when cannot get connected replicas
+	// Now, this option only works in RandomReplicaAddr function.
+	UseDisconnectedReplicas bool
+
+	// Following options are copied from Options struct.
+
+	Dialer    func(ctx context.Context, network, addr string) (net.Conn, error)
+	OnConnect func(ctx context.Context, cn *Conn) error
+
+	Protocol int
+	Username string
+	Password string
+	DB       int
+
+	MaxRetries      int
+	MinRetryBackoff time.Duration
+	MaxRetryBackoff time.Duration
+
+	DialTimeout           time.Duration
+	ReadTimeout           time.Duration
+	WriteTimeout          time.Duration
+	ContextTimeoutEnabled bool
+
+	PoolFIFO bool
+
+	PoolSize        int
+	PoolTimeout     time.Duration
+	MinIdleConns    int
+	MaxIdleConns    int
+	MaxActiveConns  int
+	ConnMaxIdleTime time.Duration
+	ConnMaxLifetime time.Duration
+
+	TLSConfig *tls.Config
+
+	DisableIndentity bool
+	IdentitySuffix   string
+	UnstableResp3    bool
+}
+
+func (opt *FailoverOptions) clientOptions() *Options {
+	return &Options{
+		Addr:       "FailoverClient",
+		ClientName: opt.ClientName,
+
+		Dialer:    opt.Dialer,
+		OnConnect: opt.OnConnect,
+
+		DB:       opt.DB,
+		Protocol: opt.Protocol,
+		Username: opt.Username,
+		Password: opt.Password,
+
+		MaxRetries:      opt.MaxRetries,
+		MinRetryBackoff: opt.MinRetryBackoff,
+		MaxRetryBackoff: opt.MaxRetryBackoff,
+
+		DialTimeout:           opt.DialTimeout,
+		ReadTimeout:           opt.ReadTimeout,
+		WriteTimeout:          opt.WriteTimeout,
+		ContextTimeoutEnabled: opt.ContextTimeoutEnabled,
+
+		PoolFIFO:        opt.PoolFIFO,
+		PoolSize:        opt.PoolSize,
+		PoolTimeout:     opt.PoolTimeout,
+		MinIdleConns:    opt.MinIdleConns,
+		MaxIdleConns:    opt.MaxIdleConns,
+		MaxActiveConns:  opt.MaxActiveConns,
+		ConnMaxIdleTime: opt.ConnMaxIdleTime,
+		ConnMaxLifetime: opt.ConnMaxLifetime,
+
+		TLSConfig: opt.TLSConfig,
+
+		DisableIndentity: opt.DisableIndentity,
+		IdentitySuffix:   opt.IdentitySuffix,
+		UnstableResp3:    opt.UnstableResp3,
+	}
+}
+
+func (opt *FailoverOptions) sentinelOptions(addr string) *Options {
+	return &Options{
+		Addr:       addr,
+		ClientName: opt.ClientName,
+
+		Dialer:    opt.Dialer,
+		OnConnect: opt.OnConnect,
+
+		DB:       0,
+		Username: opt.SentinelUsername,
+		Password: opt.SentinelPassword,
+
+		MaxRetries:      opt.MaxRetries,
+		MinRetryBackoff: opt.MinRetryBackoff,
+		MaxRetryBackoff: opt.MaxRetryBackoff,
+
+		DialTimeout:           opt.DialTimeout,
+		ReadTimeout:           opt.ReadTimeout,
+		WriteTimeout:          opt.WriteTimeout,
+		ContextTimeoutEnabled: opt.ContextTimeoutEnabled,
+
+		PoolFIFO:        opt.PoolFIFO,
+		PoolSize:        opt.PoolSize,
+		PoolTimeout:     opt.PoolTimeout,
+		MinIdleConns:    opt.MinIdleConns,
+		MaxIdleConns:    opt.MaxIdleConns,
+		MaxActiveConns:  opt.MaxActiveConns,
+		ConnMaxIdleTime: opt.ConnMaxIdleTime,
+		ConnMaxLifetime: opt.ConnMaxLifetime,
+
+		TLSConfig: opt.TLSConfig,
+
+		DisableIndentity: opt.DisableIndentity,
+		IdentitySuffix:   opt.IdentitySuffix,
+		UnstableResp3:    opt.UnstableResp3,
+	}
+}
+
+func (opt *FailoverOptions) clusterOptions() *ClusterOptions {
+	return &ClusterOptions{
+		ClientName: opt.ClientName,
+
+		Dialer:    opt.Dialer,
+		OnConnect: opt.OnConnect,
+
+		Protocol: opt.Protocol,
+		Username: opt.Username,
+		Password: opt.Password,
+
+		MaxRedirects: opt.MaxRetries,
+
+		RouteByLatency: opt.RouteByLatency,
+		RouteRandomly:  opt.RouteRandomly,
+
+		MinRetryBackoff: opt.MinRetryBackoff,
+		MaxRetryBackoff: opt.MaxRetryBackoff,
+
+		DialTimeout:           opt.DialTimeout,
+		ReadTimeout:           opt.ReadTimeout,
+		WriteTimeout:          opt.WriteTimeout,
+		ContextTimeoutEnabled: opt.ContextTimeoutEnabled,
+
+		PoolFIFO:        opt.PoolFIFO,
+		PoolSize:        opt.PoolSize,
+		PoolTimeout:     opt.PoolTimeout,
+		MinIdleConns:    opt.MinIdleConns,
+		MaxIdleConns:    opt.MaxIdleConns,
+		MaxActiveConns:  opt.MaxActiveConns,
+		ConnMaxIdleTime: opt.ConnMaxIdleTime,
+		ConnMaxLifetime: opt.ConnMaxLifetime,
+
+		TLSConfig: opt.TLSConfig,
+
+		DisableIndentity: opt.DisableIndentity,
+		IdentitySuffix:   opt.IdentitySuffix,
+	}
+}
+
+// NewFailoverClient returns a Redis client that uses Redis Sentinel
+// for automatic failover. It's safe for concurrent use by multiple
+// goroutines.
+func NewFailoverClient(failoverOpt *FailoverOptions) *Client {
+	if failoverOpt.RouteByLatency {
+		panic("to route commands by latency, use NewFailoverClusterClient")
+	}
+	if failoverOpt.RouteRandomly {
+		panic("to route commands randomly, use NewFailoverClusterClient")
+	}
+
+	sentinelAddrs := make([]string, len(failoverOpt.SentinelAddrs))
+	copy(sentinelAddrs, failoverOpt.SentinelAddrs)
+
+	rand.Shuffle(len(sentinelAddrs), func(i, j int) {
+		sentinelAddrs[i], sentinelAddrs[j] = sentinelAddrs[j], sentinelAddrs[i]
+	})
+
+	failover := &sentinelFailover{
+		opt:           failoverOpt,
+		sentinelAddrs: sentinelAddrs,
+	}
+
+	opt := failoverOpt.clientOptions()
+	opt.Dialer = masterReplicaDialer(failover)
+	opt.init()
+
+	var connPool *pool.ConnPool
+
+	rdb := &Client{
+		baseClient: &baseClient{
+			opt: opt,
+		},
+	}
+	rdb.init()
+
+	connPool = newConnPool(opt, rdb.dialHook)
+	rdb.connPool = connPool
+	rdb.onClose = failover.Close
+
+	failover.mu.Lock()
+	failover.onFailover = func(ctx context.Context, addr string) {
+		_ = connPool.Filter(func(cn *pool.Conn) bool {
+			return cn.RemoteAddr().String() != addr
+		})
+	}
+	failover.mu.Unlock()
+
+	return rdb
+}
+
+func masterReplicaDialer(
+	failover *sentinelFailover,
+) func(ctx context.Context, network, addr string) (net.Conn, error) {
+	return func(ctx context.Context, network, _ string) (net.Conn, error) {
+		var addr string
+		var err error
+
+		if failover.opt.ReplicaOnly {
+			addr, err = failover.RandomReplicaAddr(ctx)
+		} else {
+			addr, err = failover.MasterAddr(ctx)
+			if err == nil {
+				failover.trySwitchMaster(ctx, addr)
+			}
+		}
+		if err != nil {
+			return nil, err
+		}
+		if failover.opt.Dialer != nil {
+			return failover.opt.Dialer(ctx, network, addr)
+		}
+
+		netDialer := &net.Dialer{
+			Timeout:   failover.opt.DialTimeout,
+			KeepAlive: 5 * time.Minute,
+		}
+		if failover.opt.TLSConfig == nil {
+			return netDialer.DialContext(ctx, network, addr)
+		}
+		return tls.DialWithDialer(netDialer, network, addr, failover.opt.TLSConfig)
+	}
+}
+
+//------------------------------------------------------------------------------
+
+// SentinelClient is a client for a Redis Sentinel.
+type SentinelClient struct {
+	*baseClient
+	hooksMixin
+}
+
+func NewSentinelClient(opt *Options) *SentinelClient {
+	opt.init()
+	c := &SentinelClient{
+		baseClient: &baseClient{
+			opt: opt,
+		},
+	}
+
+	c.initHooks(hooks{
+		dial:    c.baseClient.dial,
+		process: c.baseClient.process,
+	})
+	c.connPool = newConnPool(opt, c.dialHook)
+
+	return c
+}
+
+func (c *SentinelClient) Process(ctx context.Context, cmd Cmder) error {
+	err := c.processHook(ctx, cmd)
+	cmd.SetErr(err)
+	return err
+}
+
+func (c *SentinelClient) pubSub() *PubSub {
+	pubsub := &PubSub{
+		opt: c.opt,
+
+		newConn: func(ctx context.Context, channels []string) (*pool.Conn, error) {
+			return c.newConn(ctx)
+		},
+		closeConn: c.connPool.CloseConn,
+	}
+	pubsub.init()
+	return pubsub
+}
+
+// Ping is used to test if a connection is still alive, or to
+// measure latency.
+func (c *SentinelClient) Ping(ctx context.Context) *StringCmd {
+	cmd := NewStringCmd(ctx, "ping")
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Subscribe subscribes the client to the specified channels.
+// Channels can be omitted to create empty subscription.
+func (c *SentinelClient) Subscribe(ctx context.Context, channels ...string) *PubSub {
+	pubsub := c.pubSub()
+	if len(channels) > 0 {
+		_ = pubsub.Subscribe(ctx, channels...)
+	}
+	return pubsub
+}
+
+// PSubscribe subscribes the client to the given patterns.
+// Patterns can be omitted to create empty subscription.
+func (c *SentinelClient) PSubscribe(ctx context.Context, channels ...string) *PubSub {
+	pubsub := c.pubSub()
+	if len(channels) > 0 {
+		_ = pubsub.PSubscribe(ctx, channels...)
+	}
+	return pubsub
+}
+
+func (c *SentinelClient) GetMasterAddrByName(ctx context.Context, name string) *StringSliceCmd {
+	cmd := NewStringSliceCmd(ctx, "sentinel", "get-master-addr-by-name", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+func (c *SentinelClient) Sentinels(ctx context.Context, name string) *MapStringStringSliceCmd {
+	cmd := NewMapStringStringSliceCmd(ctx, "sentinel", "sentinels", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Failover forces a failover as if the master was not reachable, and without
+// asking for agreement to other Sentinels.
+func (c *SentinelClient) Failover(ctx context.Context, name string) *StatusCmd {
+	cmd := NewStatusCmd(ctx, "sentinel", "failover", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Reset resets all the masters with matching name. The pattern argument is a
+// glob-style pattern. The reset process clears any previous state in a master
+// (including a failover in progress), and removes every replica and sentinel
+// already discovered and associated with the master.
+func (c *SentinelClient) Reset(ctx context.Context, pattern string) *IntCmd {
+	cmd := NewIntCmd(ctx, "sentinel", "reset", pattern)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// FlushConfig forces Sentinel to rewrite its configuration on disk, including
+// the current Sentinel state.
+func (c *SentinelClient) FlushConfig(ctx context.Context) *StatusCmd {
+	cmd := NewStatusCmd(ctx, "sentinel", "flushconfig")
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Master shows the state and info of the specified master.
+func (c *SentinelClient) Master(ctx context.Context, name string) *MapStringStringCmd {
+	cmd := NewMapStringStringCmd(ctx, "sentinel", "master", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Masters shows a list of monitored masters and their state.
+func (c *SentinelClient) Masters(ctx context.Context) *SliceCmd {
+	cmd := NewSliceCmd(ctx, "sentinel", "masters")
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Replicas shows a list of replicas for the specified master and their state.
+func (c *SentinelClient) Replicas(ctx context.Context, name string) *MapStringStringSliceCmd {
+	cmd := NewMapStringStringSliceCmd(ctx, "sentinel", "replicas", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// CkQuorum checks if the current Sentinel configuration is able to reach the
+// quorum needed to failover a master, and the majority needed to authorize the
+// failover. This command should be used in monitoring systems to check if a
+// Sentinel deployment is ok.
+func (c *SentinelClient) CkQuorum(ctx context.Context, name string) *StringCmd {
+	cmd := NewStringCmd(ctx, "sentinel", "ckquorum", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Monitor tells the Sentinel to start monitoring a new master with the specified
+// name, ip, port, and quorum.
+func (c *SentinelClient) Monitor(ctx context.Context, name, ip, port, quorum string) *StringCmd {
+	cmd := NewStringCmd(ctx, "sentinel", "monitor", name, ip, port, quorum)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Set is used in order to change configuration parameters of a specific master.
+func (c *SentinelClient) Set(ctx context.Context, name, option, value string) *StringCmd {
+	cmd := NewStringCmd(ctx, "sentinel", "set", name, option, value)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+// Remove is used in order to remove the specified master: the master will no
+// longer be monitored, and will totally be removed from the internal state of
+// the Sentinel.
+func (c *SentinelClient) Remove(ctx context.Context, name string) *StringCmd {
+	cmd := NewStringCmd(ctx, "sentinel", "remove", name)
+	_ = c.Process(ctx, cmd)
+	return cmd
+}
+
+//------------------------------------------------------------------------------
+
+type sentinelFailover struct {
+	opt *FailoverOptions
+
+	sentinelAddrs []string
+
+	onFailover func(ctx context.Context, addr string)
+	onUpdate   func(ctx context.Context)
+
+	mu          sync.RWMutex
+	_masterAddr string
+	sentinel    *SentinelClient
+	pubsub      *PubSub
+}
+
+func (c *sentinelFailover) Close() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.sentinel != nil {
+		return c.closeSentinel()
+	}
+	return nil
+}
+
+func (c *sentinelFailover) closeSentinel() error {
+	firstErr := c.pubsub.Close()
+	c.pubsub = nil
+
+	err := c.sentinel.Close()
+	if err != nil && firstErr == nil {
+		firstErr = err
+	}
+	c.sentinel = nil
+
+	return firstErr
+}
+
+func (c *sentinelFailover) RandomReplicaAddr(ctx context.Context) (string, error) {
+	if c.opt == nil {
+		return "", errors.New("opt is nil")
+	}
+
+	addresses, err := c.replicaAddrs(ctx, false)
+	if err != nil {
+		return "", err
+	}
+
+	if len(addresses) == 0 && c.opt.UseDisconnectedReplicas {
+		addresses, err = c.replicaAddrs(ctx, true)
+		if err != nil {
+			return "", err
+		}
+	}
+
+	if len(addresses) == 0 {
+		return c.MasterAddr(ctx)
+	}
+	return addresses[rand.Intn(len(addresses))], nil
+}
+
+func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
+	c.mu.RLock()
+	sentinel := c.sentinel
+	c.mu.RUnlock()
+
+	if sentinel != nil {
+		addr, err := c.getMasterAddr(ctx, sentinel)
+		if err != nil {
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return "", err
+			}
+			// Continue on other errors
+			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName name=%q failed: %s",
+				c.opt.MasterName, err)
+		} else {
+			return addr, nil
+		}
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.sentinel != nil {
+		addr, err := c.getMasterAddr(ctx, c.sentinel)
+		if err != nil {
+			_ = c.closeSentinel()
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return "", err
+			}
+			// Continue on other errors
+			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName name=%q failed: %s",
+				c.opt.MasterName, err)
+		} else {
+			return addr, nil
+		}
+	}
+
+	for i, sentinelAddr := range c.sentinelAddrs {
+		sentinel := NewSentinelClient(c.opt.sentinelOptions(sentinelAddr))
+
+		masterAddr, err := sentinel.GetMasterAddrByName(ctx, c.opt.MasterName).Result()
+		if err != nil {
+			_ = sentinel.Close()
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return "", err
+			}
+			internal.Logger.Printf(ctx, "sentinel: GetMasterAddrByName master=%q failed: %s",
+				c.opt.MasterName, err)
+			continue
+		}
+
+		// Push working sentinel to the top.
+		c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]
+		c.setSentinel(ctx, sentinel)
+
+		addr := net.JoinHostPort(masterAddr[0], masterAddr[1])
+		return addr, nil
+	}
+
+	return "", errors.New("redis: all sentinels specified in configuration are unreachable")
+}
+
+func (c *sentinelFailover) replicaAddrs(ctx context.Context, useDisconnected bool) ([]string, error) {
+	c.mu.RLock()
+	sentinel := c.sentinel
+	c.mu.RUnlock()
+
+	if sentinel != nil {
+		addrs, err := c.getReplicaAddrs(ctx, sentinel)
+		if err != nil {
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return nil, err
+			}
+			// Continue on other errors
+			internal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",
+				c.opt.MasterName, err)
+		} else if len(addrs) > 0 {
+			return addrs, nil
+		}
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.sentinel != nil {
+		addrs, err := c.getReplicaAddrs(ctx, c.sentinel)
+		if err != nil {
+			_ = c.closeSentinel()
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return nil, err
+			}
+			// Continue on other errors
+			internal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",
+				c.opt.MasterName, err)
+		} else if len(addrs) > 0 {
+			return addrs, nil
+		} else {
+			// No error and no replicas.
+			_ = c.closeSentinel()
+		}
+	}
+
+	var sentinelReachable bool
+
+	for i, sentinelAddr := range c.sentinelAddrs {
+		sentinel := NewSentinelClient(c.opt.sentinelOptions(sentinelAddr))
+
+		replicas, err := sentinel.Replicas(ctx, c.opt.MasterName).Result()
+		if err != nil {
+			_ = sentinel.Close()
+			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+				return nil, err
+			}
+			internal.Logger.Printf(ctx, "sentinel: Replicas master=%q failed: %s",
+				c.opt.MasterName, err)
+			continue
+		}
+		sentinelReachable = true
+		addrs := parseReplicaAddrs(replicas, useDisconnected)
+		if len(addrs) == 0 {
+			continue
+		}
+		// Push working sentinel to the top.
+		c.sentinelAddrs[0], c.sentinelAddrs[i] = c.sentinelAddrs[i], c.sentinelAddrs[0]
+		c.setSentinel(ctx, sentinel)
+
+		return addrs, nil
+	}
+
+	if sentinelReachable {
+		return []string{}, nil
+	}
+	return []string{}, errors.New("redis: all sentinels specified in configuration are unreachable")
+}
+
+func (c *sentinelFailover) getMasterAddr(ctx context.Context, sentinel *SentinelClient) (string, error) {
+	addr, err := sentinel.GetMasterAddrByName(ctx, c.opt.MasterName).Result()
+	if err != nil {
+		return "", err
+	}
+	return net.JoinHostPort(addr[0], addr[1]), nil
+}
+
+func (c *sentinelFailover) getReplicaAddrs(ctx context.Context, sentinel *SentinelClient) ([]string, error) {
+	addrs, err := sentinel.Replicas(ctx, c.opt.MasterName).Result()
+	if err != nil {
+		internal.Logger.Printf(ctx, "sentinel: Replicas name=%q failed: %s",
+			c.opt.MasterName, err)
+		return nil, err
+	}
+	return parseReplicaAddrs(addrs, false), nil
+}
+
+func parseReplicaAddrs(addrs []map[string]string, keepDisconnected bool) []string {
+	nodes := make([]string, 0, len(addrs))
+	for _, node := range addrs {
+		isDown := false
+		if flags, ok := node["flags"]; ok {
+			for _, flag := range strings.Split(flags, ",") {
+				switch flag {
+				case "s_down", "o_down":
+					isDown = true
+				case "disconnected":
+					if !keepDisconnected {
+						isDown = true
+					}
+				}
+			}
+		}
+		if !isDown && node["ip"] != "" && node["port"] != "" {
+			nodes = append(nodes, net.JoinHostPort(node["ip"], node["port"]))
+		}
+	}
+
+	return nodes
+}
+
+func (c *sentinelFailover) trySwitchMaster(ctx context.Context, addr string) {
+	c.mu.RLock()
+	currentAddr := c._masterAddr //nolint:ifshort
+	c.mu.RUnlock()
+
+	if addr == currentAddr {
+		return
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if addr == c._masterAddr {
+		return
+	}
+	c._masterAddr = addr
+
+	internal.Logger.Printf(ctx, "sentinel: new master=%q addr=%q",
+		c.opt.MasterName, addr)
+	if c.onFailover != nil {
+		c.onFailover(ctx, addr)
+	}
+}
+
+func (c *sentinelFailover) setSentinel(ctx context.Context, sentinel *SentinelClient) {
+	if c.sentinel != nil {
+		panic("not reached")
+	}
+	c.sentinel = sentinel
+	c.discoverSentinels(ctx)
+
+	c.pubsub = sentinel.Subscribe(ctx, "+switch-master", "+replica-reconf-done")
+	go c.listen(c.pubsub)
+}
+
+func (c *sentinelFailover) discoverSentinels(ctx context.Context) {
+	sentinels, err := c.sentinel.Sentinels(ctx, c.opt.MasterName).Result()
+	if err != nil {
+		internal.Logger.Printf(ctx, "sentinel: Sentinels master=%q failed: %s", c.opt.MasterName, err)
+		return
+	}
+	for _, sentinel := range sentinels {
+		ip, ok := sentinel["ip"]
+		if !ok {
+			continue
+		}
+		port, ok := sentinel["port"]
+		if !ok {
+			continue
+		}
+		if ip != "" && port != "" {
+			sentinelAddr := net.JoinHostPort(ip, port)
+			if !contains(c.sentinelAddrs, sentinelAddr) {
+				internal.Logger.Printf(ctx, "sentinel: discovered new sentinel=%q for master=%q",
+					sentinelAddr, c.opt.MasterName)
+				c.sentinelAddrs = append(c.sentinelAddrs, sentinelAddr)
+			}
+		}
+	}
+}
+
+func (c *sentinelFailover) listen(pubsub *PubSub) {
+	ctx := context.TODO()
+
+	if c.onUpdate != nil {
+		c.onUpdate(ctx)
+	}
+
+	ch := pubsub.Channel()
+	for msg := range ch {
+		if msg.Channel == "+switch-master" {
+			parts := strings.Split(msg.Payload, " ")
+			if parts[0] != c.opt.MasterName {
+				internal.Logger.Printf(pubsub.getContext(), "sentinel: ignore addr for master=%q", parts[0])
+				continue
+			}
+			addr := net.JoinHostPort(parts[3], parts[4])
+			c.trySwitchMaster(pubsub.getContext(), addr)
+		}
+
+		if c.onUpdate != nil {
+			c.onUpdate(ctx)
+		}
+	}
+}
+
+func contains(slice []string, str string) bool {
+	for _, s := range slice {
+		if s == str {
+			return true
+		}
+	}
+	return false
+}
+
+//------------------------------------------------------------------------------
+
+// NewFailoverClusterClient returns a client that supports routing read-only commands
+// to a replica node.
+func NewFailoverClusterClient(failoverOpt *FailoverOptions) *ClusterClient {
+	sentinelAddrs := make([]string, len(failoverOpt.SentinelAddrs))
+	copy(sentinelAddrs, failoverOpt.SentinelAddrs)
+
+	failover := &sentinelFailover{
+		opt:           failoverOpt,
+		sentinelAddrs: sentinelAddrs,
+	}
+
+	opt := failoverOpt.clusterOptions()
+	opt.ClusterSlots = func(ctx context.Context) ([]ClusterSlot, error) {
+		masterAddr, err := failover.MasterAddr(ctx)
+		if err != nil {
+			return nil, err
+		}
+
+		nodes := []ClusterNode{{
+			Addr: masterAddr,
+		}}
+
+		replicaAddrs, err := failover.replicaAddrs(ctx, false)
+		if err != nil {
+			return nil, err
+		}
+
+		for _, replicaAddr := range replicaAddrs {
+			nodes = append(nodes, ClusterNode{
+				Addr: replicaAddr,
+			})
+		}
+
+		slots := []ClusterSlot{
+			{
+				Start: 0,
+				End:   16383,
+				Nodes: nodes,
+			},
+		}
+		return slots, nil
+	}
+
+	c := NewClusterClient(opt)
+
+	failover.mu.Lock()
+	failover.onUpdate = func(ctx context.Context) {
+		c.ReloadState(ctx)
+	}
+	failover.mu.Unlock()
+
+	return c
+}