Support Redis Cluster Configuration Endpoint (#4947)

The go-redis options requires multiple redis addresses for a cluster.
In some scenarios like AWS ElastiCache, a single configuration endpoint
is used to resolve all cluster nodes.

This change adds an extra step to resolve all nodes and pass them to go-redis.
It remove the need to specify multiple cluster nodes in the configuration.

No tests were added for this scenario since it requires patching
the Go resolver during runtime.

Signed-off-by: Siavash Safi <siavash.safi@gmail.com>

docs/sources/configuration/_index.md

@@ -1747,7 +1747,7 @@ memcached_client:
   [consistent_hash: <bool>]
 
 redis:
-  # Redis Server endpoint to use for caching. A comma-separated list of endpoints
+  # Redis Server or Cluster configuration endpoint to use for caching. A comma-separated list of endpoints
   # for Redis Cluster or Redis Sentinel. If empty, no redis will be used.
   # CLI flag: -<prefix>.redis.endpoint
   [endpoint: <string>]

pkg/storage/chunk/cache/cache.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"flag"
+	"fmt"
 	"time"
 
 	"github.com/go-kit/log"
@@ -113,7 +114,11 @@ func New(cfg Config, reg prometheus.Registerer, logger log.Logger) (Cache, error
 			cfg.Redis.Expiration = cfg.DefaultValidity
 		}
 		cacheName := cfg.Prefix + "redis"
-		cache := NewRedisCache(cacheName, NewRedisClient(&cfg.Redis), logger)
+		client, err := NewRedisClient(&cfg.Redis)
+		if err != nil {
+			return nil, fmt.Errorf("redis client setup failed: %w", err)
+		}
+		cache := NewRedisCache(cacheName, client, logger)
 		caches = append(caches, NewBackground(cacheName, cfg.Background, Instrument(cacheName, cache, reg), reg))
 	}
 

pkg/storage/chunk/cache/redis_client.go

@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"flag"
 	"fmt"
+	"net"
 	"strings"
 	"time"
 	"unsafe"
@@ -31,7 +32,7 @@ type RedisConfig struct {
 
 // RegisterFlagsWithPrefix adds the flags required to config this to the given FlagSet
 func (cfg *RedisConfig) RegisterFlagsWithPrefix(prefix, description string, f *flag.FlagSet) {
-	f.StringVar(&cfg.Endpoint, prefix+"redis.endpoint", "", description+"Redis Server endpoint to use for caching. A comma-separated list of endpoints for Redis Cluster or Redis Sentinel. If empty, no redis will be used.")
+	f.StringVar(&cfg.Endpoint, prefix+"redis.endpoint", "", description+"Redis Server or Cluster configuration endpoint to use for caching. A comma-separated list of endpoints for Redis Cluster or Redis Sentinel. If empty, no redis will be used.")
 	f.StringVar(&cfg.MasterName, prefix+"redis.master-name", "", description+"Redis Sentinel master name. An empty string for Redis Server or Redis Cluster.")
 	f.DurationVar(&cfg.Timeout, prefix+"redis.timeout", 500*time.Millisecond, description+"Maximum time to wait before giving up on redis requests.")
 	f.DurationVar(&cfg.Expiration, prefix+"redis.expiration", 0, description+"How long keys stay in the redis.")
@@ -51,9 +52,27 @@ type RedisClient struct {
 }
 
 // NewRedisClient creates Redis client
-func NewRedisClient(cfg *RedisConfig) *RedisClient {
+func NewRedisClient(cfg *RedisConfig) (*RedisClient, error) {
+	endpoints := strings.Split(cfg.Endpoint, ",")
+	// Handle single configuration endpoint which resolves multiple nodes.
+	if len(endpoints) == 1 {
+		host, port, err := net.SplitHostPort(endpoints[0])
+		if err != nil {
+			return nil, err
+		}
+		addrs, err := net.LookupHost(host)
+		if err != nil {
+			return nil, err
+		}
+		if len(addrs) > 1 {
+			endpoints = nil
+			for _, addr := range addrs {
+				endpoints = append(endpoints, net.JoinHostPort(addr, port))
+			}
+		}
+	}
 	opt := &redis.UniversalOptions{
-		Addrs:       strings.Split(cfg.Endpoint, ","),
+		Addrs:       endpoints,
 		MasterName:  cfg.MasterName,
 		Password:    cfg.Password.Value,
 		DB:          cfg.DB,
@@ -68,7 +87,7 @@ func NewRedisClient(cfg *RedisConfig) *RedisClient {
 		expiration: cfg.Expiration,
 		timeout:    cfg.Timeout,
 		rdb:        redis.NewUniversalClient(opt),
-	}
+	}, nil
 }
 
 func (c *RedisClient) Ping(ctx context.Context) error {