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package sentinel
import (
"errors"
"fmt"
"net"
"strings"
"sync"
"time"
"github.com/gomodule/redigo/redis"
)
// Sentinel provides a way to add high availability (HA) to Redis Pool using
// preconfigured addresses of Sentinel servers and name of master which Sentinels
// monitor. It works with Redis >= 2.8.12 (mostly because of ROLE command that
// was introduced in that version, it's possible though to support old versions
// using INFO command).
//
// Example of the simplest usage to contact master "mymaster":
//
// func newSentinelPool() *redis.Pool {
// sntnl := &sentinel.Sentinel{
// Addrs: []string{":26379", ":26380", ":26381"},
// MasterName: "mymaster",
// Dial: func(addr string) (redis.Conn, error) {
// timeout := 500 * time.Millisecond
// c, err := redis.DialTimeout("tcp", addr, timeout, timeout, timeout)
// if err != nil {
// return nil, err
// }
// return c, nil
// },
// }
// return &redis.Pool{
// MaxIdle: 3,
// MaxActive: 64,
// Wait: true,
// IdleTimeout: 240 * time.Second,
// Dial: func() (redis.Conn, error) {
// masterAddr, err := sntnl.MasterAddr()
// if err != nil {
// return nil, err
// }
// c, err := redis.Dial("tcp", masterAddr)
// if err != nil {
// return nil, err
// }
// return c, nil
// },
// TestOnBorrow: func(c redis.Conn, t time.Time) error {
// if !sentinel.TestRole(c, "master") {
// return errors.New("Role check failed")
// } else {
// return nil
// }
// },
// }
// }
type Sentinel struct {
// Addrs is a slice with known Sentinel addresses.
Addrs []string
// MasterName is a name of Redis master Sentinel servers monitor.
MasterName string
// Dial is a user supplied function to connect to Sentinel on given address. This
// address will be chosen from Addrs slice.
// Note that as per the redis-sentinel client guidelines, a timeout is mandatory
// while connecting to Sentinels, and should not be set to 0.
Dial func(addr string) (redis.Conn, error)
// Pool is a user supplied function returning custom connection pool to Sentinel.
// This can be useful to tune options if you are not satisfied with what default
// Sentinel pool offers. See defaultPool() method for default pool implementation.
// In most cases you only need to provide Dial function and let this be nil.
Pool func(addr string) *redis.Pool
mu sync.RWMutex
pools map[string]*redis.Pool
addr string
}
// NoSentinelsAvailable is returned when all sentinels in the list are exhausted
// (or none configured), and contains the last error returned by Dial (which
// may be nil)
type NoSentinelsAvailable struct {
lastError error
}
func (ns NoSentinelsAvailable) Error() string {
if ns.lastError != nil {
return fmt.Sprintf("redigo: no sentinels available; last error: %s", ns.lastError.Error())
}
return fmt.Sprintf("redigo: no sentinels available")
}
// putToTop puts Sentinel address to the top of address list - this means
// that all next requests will use Sentinel on this address first.
//
// From Sentinel guidelines:
//
// The first Sentinel replying to the client request should be put at the
// start of the list, so that at the next reconnection, we'll try first
// the Sentinel that was reachable in the previous connection attempt,
// minimizing latency.
//
// Lock must be held by caller.
func (s *Sentinel) putToTop(addr string) {
addrs := s.Addrs
if addrs[0] == addr {
// Already on top.
return
}
newAddrs := []string{addr}
for _, a := range addrs {
if a == addr {
continue
}
newAddrs = append(newAddrs, a)
}
s.Addrs = newAddrs
}
// putToBottom puts Sentinel address to the bottom of address list.
// We call this method internally when see that some Sentinel failed to answer
// on application request so next time we start with another one.
//
// Lock must be held by caller.
func (s *Sentinel) putToBottom(addr string) {
addrs := s.Addrs
if addrs[len(addrs)-1] == addr {
// Already on bottom.
return
}
newAddrs := []string{}
for _, a := range addrs {
if a == addr {
continue
}
newAddrs = append(newAddrs, a)
}
newAddrs = append(newAddrs, addr)
s.Addrs = newAddrs
}
// defaultPool returns a connection pool to one Sentinel. This allows
// us to call concurrent requests to Sentinel using connection Do method.
func (s *Sentinel) defaultPool(addr string) *redis.Pool {
return &redis.Pool{
MaxIdle: 3,
MaxActive: 10,
Wait: true,
IdleTimeout: 240 * time.Second,
Dial: func() (redis.Conn, error) {
return s.Dial(addr)
},
TestOnBorrow: func(c redis.Conn, t time.Time) error {
_, err := c.Do("PING")
return err
},
}
}
func (s *Sentinel) get(addr string) redis.Conn {
pool := s.poolForAddr(addr)
return pool.Get()
}
func (s *Sentinel) poolForAddr(addr string) *redis.Pool {
s.mu.Lock()
if s.pools == nil {
s.pools = make(map[string]*redis.Pool)
}
pool, ok := s.pools[addr]
if ok {
s.mu.Unlock()
return pool
}
s.mu.Unlock()
newPool := s.newPool(addr)
s.mu.Lock()
p, ok := s.pools[addr]
if ok {
s.mu.Unlock()
return p
}
s.pools[addr] = newPool
s.mu.Unlock()
return newPool
}
func (s *Sentinel) newPool(addr string) *redis.Pool {
if s.Pool != nil {
return s.Pool(addr)
}
return s.defaultPool(addr)
}
// close connection pool to Sentinel.
// Lock must be hold by caller.
func (s *Sentinel) close() {
if s.pools != nil {
for _, pool := range s.pools {
pool.Close()
}
}
s.pools = nil
}
func (s *Sentinel) doUntilSuccess(f func(redis.Conn) (interface{}, error)) (interface{}, error) {
s.mu.RLock()
addrs := s.Addrs
s.mu.RUnlock()
var lastErr error
for _, addr := range addrs {
conn := s.get(addr)
reply, err := f(conn)
conn.Close()
if err != nil {
lastErr = err
s.mu.Lock()
pool, ok := s.pools[addr]
if ok {
pool.Close()
delete(s.pools, addr)
}
s.putToBottom(addr)
s.mu.Unlock()
continue
}
s.putToTop(addr)
return reply, nil
}
return nil, NoSentinelsAvailable{lastError: lastErr}
}
// MasterAddr returns an address of current Redis master instance.
func (s *Sentinel) MasterAddr() (string, error) {
res, err := s.doUntilSuccess(func(c redis.Conn) (interface{}, error) {
return queryForMaster(c, s.MasterName)
})
if err != nil {
return "", err
}
return res.(string), nil
}
// SlaveAddrs returns a slice with known slave addresses of current master instance.
func (s *Sentinel) SlaveAddrs() ([]string, error) {
res, err := s.doUntilSuccess(func(c redis.Conn) (interface{}, error) {
return queryForSlaveAddrs(c, s.MasterName)
})
if err != nil {
return nil, err
}
return res.([]string), nil
}
// Slave represents a Redis slave instance which is known by Sentinel.
type Slave struct {
ip string
port string
flags string
}
// Addr returns an address of slave.
func (s *Slave) Addr() string {
return net.JoinHostPort(s.ip, s.port)
}
// Available returns if slave is in working state at moment based on information in slave flags.
func (s *Slave) Available() bool {
return !strings.Contains(s.flags, "disconnected") && !strings.Contains(s.flags, "s_down")
}
// Slaves returns a slice with known slaves of master instance.
func (s *Sentinel) Slaves() ([]*Slave, error) {
res, err := s.doUntilSuccess(func(c redis.Conn) (interface{}, error) {
return queryForSlaves(c, s.MasterName)
})
if err != nil {
return nil, err
}
return res.([]*Slave), nil
}
// SentinelAddrs returns a slice of known Sentinel addresses Sentinel server aware of.
func (s *Sentinel) SentinelAddrs() ([]string, error) {
res, err := s.doUntilSuccess(func(c redis.Conn) (interface{}, error) {
return queryForSentinels(c, s.MasterName)
})
if err != nil {
return nil, err
}
return res.([]string), nil
}
// Discover allows to update list of known Sentinel addresses. From docs:
//
// A client may update its internal list of Sentinel nodes following this procedure:
// 1) Obtain a list of other Sentinels for this master using the command SENTINEL sentinels <master-name>.
// 2) Add every ip:port pair not already existing in our list at the end of the list.
func (s *Sentinel) Discover() error {
addrs, err := s.SentinelAddrs()
if err != nil {
return err
}
s.mu.Lock()
for _, addr := range addrs {
if !stringInSlice(addr, s.Addrs) {
s.Addrs = append(s.Addrs, addr)
}
}
s.mu.Unlock()
return nil
}
// Close closes current connection to Sentinel.
func (s *Sentinel) Close() error {
s.mu.Lock()
s.close()
s.mu.Unlock()
return nil
}
// TestRole wraps GetRole in a test to verify if the role matches an expected
// role string. If there was any error in querying the supplied connection,
// the function returns false. Works with Redis >= 2.8.12.
// It's not goroutine safe, but if you call this method on pooled connections
// then you are OK.
func TestRole(c redis.Conn, expectedRole string) bool {
role, err := getRole(c)
if err != nil || role != expectedRole {
return false
}
return true
}
// getRole is a convenience function supplied to query an instance (master or
// slave) for its role. It attempts to use the ROLE command introduced in
// redis 2.8.12.
func getRole(c redis.Conn) (string, error) {
res, err := c.Do("ROLE")
if err != nil {
return "", err
}
rres, ok := res.([]interface{})
if ok {
return redis.String(rres[0], nil)
}
return "", errors.New("redigo: can not transform ROLE reply to string")
}
func queryForMaster(conn redis.Conn, masterName string) (string, error) {
res, err := redis.Strings(conn.Do("SENTINEL", "get-master-addr-by-name", masterName))
if err != nil {
return "", err
}
if len(res) < 2 {
return "", errors.New("redigo: malformed get-master-addr-by-name reply")
}
masterAddr := net.JoinHostPort(res[0], res[1])
return masterAddr, nil
}
func queryForSlaveAddrs(conn redis.Conn, masterName string) ([]string, error) {
slaves, err := queryForSlaves(conn, masterName)
if err != nil {
return nil, err
}
slaveAddrs := make([]string, 0)
for _, slave := range slaves {
slaveAddrs = append(slaveAddrs, slave.Addr())
}
return slaveAddrs, nil
}
func queryForSlaves(conn redis.Conn, masterName string) ([]*Slave, error) {
res, err := redis.Values(conn.Do("SENTINEL", "slaves", masterName))
if err != nil {
return nil, err
}
slaves := make([]*Slave, 0)
for _, a := range res {
sm, err := redis.StringMap(a, err)
if err != nil {
return slaves, err
}
slave := &Slave{
ip: sm["ip"],
port: sm["port"],
flags: sm["flags"],
}
slaves = append(slaves, slave)
}
return slaves, nil
}
func queryForSentinels(conn redis.Conn, masterName string) ([]string, error) {
res, err := redis.Values(conn.Do("SENTINEL", "sentinels", masterName))
if err != nil {
return nil, err
}
sentinels := make([]string, 0)
for _, a := range res {
sm, err := redis.StringMap(a, err)
if err != nil {
return sentinels, err
}
sentinels = append(sentinels, fmt.Sprintf("%s:%s", sm["ip"], sm["port"]))
}
return sentinels, nil
}
func stringInSlice(str string, slice []string) bool {
for _, s := range slice {
if s == str {
return true
}
}
return false
}
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