Redis Master‑Slave Replication: Configuration and Operation Guide

Redis supports master‑slave replication, allowing data to be synchronized from a master server to any number of slave servers, which can themselves act as masters for further slaves, forming a single‑level tree replication that enhances read scalability and data redundancy.

The replication architecture can be a one‑master‑multiple‑slaves or a cascaded structure, and synchronization occurs either as a full sync (initial copy) or an incremental sync (subsequent changes).

Full synchronization proceeds through the following steps:

1) The slave connects to the master and sends the SYNC command. 2) The master receives SYNC, runs BGSAVE to generate an RDB snapshot while buffering subsequent write commands. 3) After BGSAVE completes, the master streams the snapshot to all slaves, continuing to record writes. 4) The slave discards old data, loads the received snapshot. 5) Once the snapshot transfer finishes, the master streams buffered write commands to the slaves. 6) The slave, after loading the snapshot, starts applying the buffered write commands.

Key configuration parameters in /etc/redis/redis.conf include:

daemonize yes

pidfile "/var/run/redis6379.pid"

port 6379

timeout 0

loglevel notice

logfile "stdout"

databases 16

save 900 1

save 300 10

save 60 10000

stop-writes-on-bgsave-error yes

rdbcompression yes

rdbchecksum yes

dbfilename "dump.rdb"

dir "/data/redis_db/6378"

protected-mode no

replica-serve-stale-data yes

replica-read-only yes

requirepass 123456

maxmemory 20gb

appendonly no

appendfsync everysec

auto-aof-rewrite-percentage 100

auto-aof-rewrite-min-size 64mb

lua-time-limit 5000

slowlog-log-slower-than 10000

client-output-buffer-limit normal 0 0 0

client-output-buffer-limit replica 256mb 64mb 60

client-output-buffer-limit pubsub 32mb 8mb 60

hz 10

maxclients 50000

To configure replication, execute on the slave:

127.0.0.1:6379> SLAVEOF 192.168.20.8 6378

127.0.0.1:6379> CONFIG set masterauth 123456

Verify synchronization on the slave with: 127.0.0.1:6379> INFO Replication The output shows role:slave, master host/port, link status, and replication offsets, confirming the connection.

On the master, test data replication by setting keys:

127.0.0.1:6378> set name age

127.0.0.1:6378> set k1 v1

Reading the keys on the slave returns the same values, demonstrating successful replication: 127.0.0.1:6379> get name →

"age"

127.0.0.1:6379> get k1

→ "v1" This guide provides a complete walkthrough for setting up, configuring, and testing Redis master‑slave replication.