Question: What is the replication strategy in Redis?

Answer

Redis uses a master-slave model for its replication strategy. By default, all data written to the master will be asynchronously replicated to any connected slaves.

When setting up replication, you typically begin by configuring one or more slave instances to connect to a master instance. This is done using the SLAVEOF command:

SLAVEOF master_host master_port

Once this command is issued, the slave will start replicating data from the master. If the dataset is large, it may take some time for the initial synchronization to complete.

The real charm of Redis' replication strategy comes with its ability to handle network splits and automatic failover. When a master goes down, one of the slaves can be promoted to become the new master, ensuring that your service remains available even if the original master fails.

Redis Sentinel is a system designed by the Redis team for managing these automatic failovers. It monitors your master and slave instances, providing automated failover if the master becomes unreachable.

With Redis Cluster, both read and write operations can be distributed among multiple nodes, which allows for automatic partitioning across several Redis nodes. Thus, it offers another level of replication strategy where the data is automatically partitioned across multiple nodes and also provides some degree of availability during network partitions.

It's notable to mention that while replication provides a level of redundancy, it should not be relied upon as a sole means of data persistence - instead, it should be used in conjunction with other methods like Redis persistence (RDB or AOF), especially for critical data.