Redis Cheatsheet 12 — Redis Cluster

# 6 nodes (3 primaries + 3 replicas)
for port in 7000 7001 7002 7003 7004 7005; do
    mkdir $port && cd $port
    cat > redis.conf <<EOF
port $port
cluster-enabled yes
cluster-config-file nodes.conf
cluster-node-timeout 5000
appendonly yes
EOF
    redis-server redis.conf &
    cd ..
done

redis-cli --cluster create 127.0.0.1:7000 ... 127.0.0.1:7005 --cluster-replicas 1

16384 slots total, distributed across primaries.
key → CRC16(key) % 16384 → slot → node.

SET {user:1}:profile ...
SET {user:1}:sessions ...

from redis.cluster import RedisCluster
client = RedisCluster(host="node1", port=7000)

# Cluster-aware: routes to correct node, handles MOVED redirects.

redis-cli --cluster reshard 127.0.0.1:7000
# Interactive: how many slots, from where, to where

redis-cli --cluster add-node 127.0.0.1:7006 127.0.0.1:7000
# Then reshard to give it slots

redis-cli --cluster reshard ... (move slots away)
redis-cli --cluster del-node 127.0.0.1:7000 <node-id>

redis-cli -p 7004 CLUSTER FAILOVER  # on replica

redis-cli -p 7000 CLUSTER INFO
redis-cli -p 7000 CLUSTER NODES
redis-cli -p 7000 CLUSTER SLOTS

for key in cluster.scan_iter(match="user:*"):
    ...

# Only works if keys hash to same slot
client.mget("{u:1}:a", "{u:1}:b")        # ok
client.mget("a", "b")                     # may fail with CROSSSLOT

SSUBSCRIBE channel
SPUBLISH channel msg

client.execute_command("READONLY")
# Then reads route to replicas