add basic support for redis cluster server (#9128)

This change updates the central utility class to recognize a Redis
cluster server after connection and returns an new cluster aware Redis
client. The "normal" Redis client would not be able to talk to a cluster
node because keys might be stored on other shards of the Redis cluster
and therefor not readable or writable.

With this patch clients do not need to know what Redis server it is,
they just connect though the same API calls for standalone and cluster
server.

There are no dependencies added due to this MR.

Remark - with current redis-py client library (4.6.0) a cluster cannot
be used as VectorStore. It can be used for other use-cases. There is a
bug / missing feature(?) in the Redis client breaking the VectorStore
implementation. I opened an issue at the client library too
(redis/redis-py#2888) to fix this. As soon as this is fixed in
`redis-py` library it should be usable there too.

---------

Co-authored-by: Bagatur <[email protected]>

libs/langchain/langchain/utilities/redis.py

@@ -68,14 +68,17 @@ def get_client(redis_url: str, **kwargs: Any) -> RedisType:
     # check if normal redis:// or redis+sentinel:// url
     if redis_url.startswith("redis+sentinel"):
         redis_client = _redis_sentinel_client(redis_url, **kwargs)
-    if redis_url.startswith("rediss+sentinel"):  # sentinel with TLS support enables
+    elif redis_url.startswith("rediss+sentinel"):  # sentinel with TLS support enables
         kwargs["ssl"] = True
         if "ssl_cert_reqs" not in kwargs:
             kwargs["ssl_cert_reqs"] = "none"
         redis_client = _redis_sentinel_client(redis_url, **kwargs)
     else:
-        # connect to redis server from url
+        # connect to redis server from url, reconnect with cluster client if needed
         redis_client = redis.from_url(redis_url, **kwargs)
+        if _check_for_cluster(redis_client):
+            redis_client.close()
+            redis_client = _redis_cluster_client(redis_url, **kwargs)
     return redis_client
 
 
@@ -138,3 +141,19 @@ def _redis_sentinel_client(redis_url: str, **kwargs: Any) -> RedisType:
             raise ae
 
     return sentinel_client.master_for(service_name)
+
+
+def _check_for_cluster(redis_client: RedisType) -> bool:
+    import redis
+
+    try:
+        cluster_info = redis_client.info("cluster")
+        return cluster_info["cluster_enabled"] == 1
+    except redis.exceptions.RedisError:
+        return False
+
+
+def _redis_cluster_client(redis_url: str, **kwargs: Any) -> RedisType:
+    from redis.cluster import RedisCluster
+
+    return RedisCluster.from_url(redis_url, **kwargs)