Redis Cluster: Architecture, Setup, Testing, and High Availability

Redis provides a high‑availability solution called Sentinel, but its single‑master design limits storage capacity and performance for large‑scale data; Redis Cluster addresses this by sharding data across multiple nodes, greatly increasing capacity and horizontal scalability.

The cluster consists of 16384 hash slots; each key is hashed (CRC16) and assigned to a slot, which determines the node responsible for that key. Nodes manage specific slot ranges, enabling efficient data distribution.

To set up a Redis Cluster on a single server, create separate directories for each port (7000‑7005) and copy a base redis.conf into each, modifying parameters such as port , cluster-enabled yes , cluster-config-file , cluster-node-timeout , and authentication settings.

port 7000
cluster-enabled yes
cluster-config-file nodes-7000.conf
cluster-node-timeout 5000
dbfilename "dump-7000.rdb"
protected-mode no
logfile "logfile-7000.log"
requirepass 123456
masterauth 123456
pidfile "redis_7000.pid"

Create the directory structure and start each instance:

mkdir cluster-test
cd cluster-test
mkdir 7000 7001 7002 7003 7004 7005
./redis-server ./cluster-test/7000/redis.conf &
./redis-server ./cluster-test/7001/redis.conf &
./redis-server ./cluster-test/7002/redis.conf &
./redis-server ./cluster-test/7003/redis.conf &
./redis-server ./cluster-test/7004/redis.conf &
./redis-server ./cluster-test/7005/redis.conf &

After the nodes are running, create the cluster with:

redis-cli --cluster create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:7004 127.0.0.1:7005 --cluster-replicas 1 -a 123456

The command distributes the 16384 slots among the three master nodes (each with a replica), and the output confirms slot allocation and node roles.

Testing the cluster with redis-cli -h 127.0.0.1 -p 7000 -c -a 123456 shows automatic redirection based on slot calculation:

127.0.0.1:7000> set slogan good
-> Redirected to slot [16191] located at 127.0.0.1:7002
OK
127.0.0.1:7000> get slogan
-> Redirected to slot [16191] located at 127.0.0.1:7002
"good"

Failover is demonstrated by stopping a master (e.g., port 7002); the corresponding slave (port 7003) is promoted to master, and the original master becomes a slave when it rejoins.

Cluster health can be inspected with redis-cli --cluster check 127.0.0.1:7000 -a 123456 , which reports slot coverage, master/slave roles, and key distribution.

Overall, Redis Cluster provides strong scalability and high availability through data sharding and automatic failover, making it a more advanced solution than Sentinel for demanding workloads.