Redis Replication Fundamentals

Redis replication enables automatic data synchronization from a primary node (master) to replica nodes (slaves). The master handles write operations while replicas serve read requests.

Replicatino Mechanism

1. Replicas initiate synchronization by sending a SYNC command to the master
2. The master starts a background save process and collects modification commands
3. Full synchronization: Master transfers the entire dataset to the replica
4. Incremental synchronization: Master streams subsequent modification commands
5. Full resynchronization occurs automatically when replicas reconnect

Configuration Setup

Configure replicas without modifying the master:

# Configure replica
replicaof <master_ip> <master_port>
# Verify configuration
info replication

Persistent configuration requiers adding to redis.conf.

Multi-Instance Setup

1. Duplicate redis.conf as redis[port].conf

2. Enable daemon mode: daemonize yes

3. Set unique ports and filenames: ```

   port 7000 dbfilename dump7000.rdb logfile redis7000.log

Replication Topologies

Single Master with Multiple Replicas

# Replica 7001 configuration
replicaof 127.0.0.1 7000

# Replica 7002 configuration
replicaof 127.0.0.1 7000

Key characteristics:

• Replicas are read-only
• Master failure leaves replicas in standby
• Initial connection triggers full synchronization

Chained Replication

# Tiered replication setup
replica1: replicaof 127.0.0.1 7000
replica2: replicaof 127.0.0.1 7001

Intermediate replicas reduce write load on the primary master.

Failover Procedure

# Promote replica to master
REPLICAOF no one

# Redirect other replicas
replicaof 127.0.0.1 7001

Sentinel-Based High Availability

Redis Sentinel automates failover detection and management.

Configuration Steps

# sentinel.conf
sentinel monitor primary-cluster 127.0.0.1 7000 2

Key parameters:

• Quorum: Minimum votes to trigger failover
• Leader election requires majority consensus

Failover Process

1. Sentinels detect master failure
2. Elected leader initiates failover
3. New master selected from replicas
4. Original master becomes replica upon recovery

Replication Limitations

Synchronization latency may occur during high-write workloads, particularly with numerous replicas.