Redis replicaof 命令
REPLICAOF host port
The REPLICAOF command can change the replication settings of a replica on the fly.
If a Redis server is already acting as replica, the command REPLICAOF NO ONE will turn off the replication, turning the Redis server into a MASTER. In the proper form REPLICAOF hostname port will make the server a replica of another server listening at the specified hostname and port.
If a server is already a replica of some master, REPLICAOF hostname port will stop the replication against the old server and start the synchronization against the new one, discarding the old dataset.
The form REPLICAOF NO ONE will stop replication, turning the server into a MASTER, but will not discard the replication. So, if the old master stops working, it is possible to turn the replica into a master and set the application to use this new master in read/write. Later when the other Redis server is fixed, it can be reconfigured to work as a replica.