Creating a Redis Cluster

I wanted to test out running a Redis cluster, this is what I did:

Install redis itself

# apt-get install redis

This gives you a running Redis instance on your machine. However, it's only its binaries that we're really after here.

Create six Redis nodes

$ mkdir {7000..70005
$ for el in {7000..7005}; do
  cat > $el/redis.conf <<EOF
port $el
cluster-enabled yes
cluster-config-file nodes.conf
cluster-node-timeout 5000

Start the Six Redis nodes

$ for el in {7000..7005}; do
    (cd $el && nohup redis-server ./redis.conf & )

Create the Redis cluster

$ redis-cli \
  --cluster create \ \ \ \ \ \ \
  --cluster-replicas 1

This will create one replica for each of the masters. So the above will create 3 masters and 3 replicas. This means Redis has some redundancy, but if both the master and its replica goes down, the other nodes will not be able to recover the data.

If you download the Redis source code, you can find a script that does all of this for you (but what's the fun in that 😉).

Writing data on one node and retrieving it from another

root@redis:~# redis-cli -c -p 7001> set user1 "john set on 7001"
root@redis:~# redis-cli -c -p 7004> get user1
-> Redirected to slot [8106] located at
"john set on 7001">

Notice that, even though we queried a different node for the data we wrote to 7001, we were still redirected to 7001 when asking 7004 for the data. This shows the high performance, sharding nature of how Redis works - at the expense of redundancy/recovery. To mitigate this, you can have more than one replica per master.

Happy caching!

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