cacheutil: adding support for Redis Sentinel

Add a new option `master_name` that if not empty chooses the appropriate
master. Reusing terminology used by Cortex and official Redis
documentation (https://redis.io/docs/management/sentinel/).

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>

CHANGELOG.md

@@ -29,6 +29,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#5889](https://github.com/thanos-io/thanos/pull/5889) Query Frontend: Support sharding vertical sharding `label_replace` and `label_join` functions.
 - [#5819](https://github.com/thanos-io/thanos/pull/5819) Store: Add a few objectives for Store's data touched/fetched amount and sizes. They are: 50, 95, and 99 quantiles.
 - [#5940](https://github.com/thanos-io/thanos/pull/5940) Objstore: Support for authenticating to Swift using application credentials.
+- [#5990](https://github.com/thanos-io/thanos/pull/5990) Cache/Redis: add support for Redis Sentinel via new option `master_name`.
 
 ### Changed
 

docs/components/query-frontend.md

@@ -133,6 +133,7 @@ config:
     server_name: ""
     insecure_skip_verify: false
   cache_size: 0
+  master_name: ""
   expiration: 24h0m0s
 ```
 

docs/components/store.md

@@ -343,6 +343,7 @@ config:
     server_name: ""
     insecure_skip_verify: false
   cache_size: 0
+  master_name: ""
 ```
 
 The **required** settings are:

pkg/cacheutil/redis_client.go

@@ -125,6 +125,10 @@ type RedisClientConfig struct {
 	// instead of fetching data each time.
 	// See https://redis.io/docs/manual/client-side-caching/ for info.
 	CacheSize model.Bytes `yaml:"cache_size"`
+
+	// MasterName specifies the master's name. Must be not empty
+	// for Redis Sentinel.
+	MasterName string `yaml:"master_name"`
 }
 
 func (c *RedisClientConfig) validate() error {
@@ -194,7 +198,7 @@ func NewRedisClientWithConfig(logger log.Logger, name string, config RedisClient
 		clientSideCacheDisabled = true
 	}
 
-	client, err := rueidis.NewClient(rueidis.ClientOption{
+	clientOpts := rueidis.ClientOption{
 		InitAddress:       strings.Split(config.Addr, ","),
 		ShuffleInit:       true,
 		Username:          config.Username,
@@ -205,7 +209,15 @@ func NewRedisClientWithConfig(logger log.Logger, name string, config RedisClient
 		ConnWriteTimeout:  config.WriteTimeout,
 		DisableCache:      clientSideCacheDisabled,
 		TLSConfig:         tlsConfig,
-	})
+	}
+
+	if config.MasterName != "" {
+		clientOpts.Sentinel = rueidis.SentinelOption{
+			MasterSet: config.MasterName,
+		}
+	}
+
+	client, err := rueidis.NewClient(clientOpts)
 	if err != nil {
 		return nil, err
 	}