Implementing Replication

1. Configuring Master Server

Directive	Description
`requirepass`	Set master password
`masterauth`	Used when promoted to replica
`repl-backlog-size 64mb`	Buffer for partial resync

replicaof master.host 6379
masterauth secret
replica-read-only yes

Command	Description
`REPLICAOF host port`	Runtime configure replication
`REPLICAOF NO ONE`	Detach and become master

Directive	Default
`replica-read-only yes`	Reject writes (recommended)

Command	Returns
`INFO replication`	Role, connected replicas, offsets
`ROLE`	master/slave/sentinel with details

Command	Description
`REPLICAOF NO ONE`	Manual promotion
Sentinel	Automatic on failover

Directive	Effect
`repl-diskless-sync yes`	Stream RDB over socket without intermediate file
`repl-diskless-sync-delay 5`	Wait to batch replicas
`repl-diskless-load on-empty-db`	Replica loads from socket without disk

Directive	Default
`repl-timeout 60`	Seconds before disconnect
`repl-ping-replica-period 10`	Keepalive interval

Directive	Detail
`repl-backlog-size`	Size of replication ring buffer
`repl-backlog-ttl`	Drop backlog after N seconds of no replicas

Command	Returns
`WAIT numreplicas timeout-ms`	Number of replicas that ACK'd

Command	Description
`WAITAOF numlocal numreplicas timeout-ms`	Wait for AOF fsync on local + N replicas 7.2+

Metric	Source
master_repl_offset − slave_repl_offset	`INFO replication`
lag (seconds)	Per-replica in master INFO

Field	Detail
master_replid	Replication group ID
repl_backlog_active	1 if backlog enabled

Pattern	Detail
Read from replicas	Use `READONLY` in Cluster context
Eventual consistency	Reads may lag master
`min-replicas-to-write n`	Refuse writes if too few replicas online