Redis Cluster

DCS provides two types of cluster Redis instances: Proxy Cluster and Redis Cluster. Proxy Cluster uses Linux Virtual Server (LVS) and proxies. Redis Cluster is the native distributed implementation of Redis. Proxy Cluster instances are compatible with Redis 3.0, while Redis Cluster instances are compatible with Redis 4.0 and 5.0.

This section describes Redis Cluster DCS Redis 4.0 and 5.0 instances.

Redis Cluster DCS Redis 4.0 and 5.0 Instances

The Redis Cluster instance type provided by DCS is compatible with the native Redis Cluster, which uses smart clients and a distributed architecture to perform sharding.

Table 1 lists the shard specification for different instance specifications.

Specification per shard=Instance specification/Number of shards. For example, if a 48 GB instance has 6 shards, the specification of each shard is 48 GB/6 = 8 GB.

**Table 1** Specifications of Redis Cluster DCS instances
Total Memory	Shards
4 GB/8 GB/16 GB/24 GB/32 GB	3
48 GB	6
64 GB	8
96 GB	12
128 GB	16
192 GB	24
256 GB	32
384 GB	48
512 GB	64
768 GB	96
1024 GB	128

Distributed architecture
Any node in a Redis Cluster can receive requests. Received requests are then redirected to the right node for processing. Each node consists of a subset of one master and one (by default) or multiple replicas. The master or replica roles are determined through an election algorithm.

Figure 1 Distributed architecture of Redis Cluster
Presharding
There are 16,384 hash slots in each Redis Cluster. The mapping between hash slots and Redis nodes is stored in Redis Servers. To compute what is the hash slot of a given key, simply take the CRC16 of the key modulo 16384. Example command output

Figure 2 Redis Cluster presharding