Add db_index option to Redis cache configuration (#380)

* Add db_index option to Redis cache configuration

* Clarify db_index use in Redis config docs

---------

Co-authored-by: solodovnikov_ny <solodovnikov_ny@magnit.ru>

clients/redis.go

@@ -16,6 +16,11 @@ func NewRedisClient(cfg config.RedisCacheConfig) (redis.UniversalClient, error)
 		MaxRetries: 7, // default value = 3, since MinRetryBackoff = 8 msec & MinRetryBackoff = 512 msec
 		// the redis client will wait up to 1016 msec btw the 7 tries
 	}
+
+	if len(cfg.Addresses) == 1 {
+		options.DB = cfg.DBIndex
+	}
+
 	if len(cfg.CertFile) != 0 || len(cfg.KeyFile) != 0 {
 		tlsConfig, err := cfg.TLS.BuildTLSConfig(nil)
 		if err != nil {

config/README.md

@@ -111,6 +111,7 @@ redis:
     - <string> # example "localhost:6379"
   username: <string>
   password: <string>
+  db_index: <int> | default = 0 [optional] # This option is only applicable for non-clustered Redis instance.
 
 # Expiration time for cached responses.
 expire: <duration>

config/config.go

@@ -949,6 +949,7 @@ type RedisCacheConfig struct {
 	Username  string                 `yaml:"username,omitempty"`
 	Password  string                 `yaml:"password,omitempty"`
 	Addresses []string               `yaml:"addresses"`
+	DBIndex   int                    `yaml:"db_index,omitempty"`
 	XXX       map[string]interface{} `yaml:",inline"`
 }