How Redis supports high availability

Redis high availability mechanism

Redis is a high availability (HA) distributed cache system that can be implemented through the following mechanisms:

Master-slave copy

• Master-slave replication creates a replication group of master and multiple slave nodes.
• The master node stores data and replicates it synchronously to the slave node.
• The slave node can handle read requests, reducing the load on the master node.
• If the master node fails, you can quickly promote a slave node to a master node.

sentinel

• Sentinel is an independent process responsible for monitoring the master-slave replication group.
• When the master node fails, the sentry triggers the failover process, promoting a slave node to the master node.
• Sentinels can also perform failover between master and slave nodes.

Cluster

• A Redis cluster is a fully distributed system with no master-slave relationship.
• Each node in the cluster stores a portion of the data.
• The cluster uses a consistent hash to allocate data, and each node is responsible for the hash range of keys.
• The cluster achieves high availability because even if one node fails, other nodes can still provide services.

Client failover

• Client failover allows the client to automatically switch to the new master node after failover.
• Clients usually use connection pools, and when the primary node fails, the client pool automatically tries to connect to the new primary node.

Other Features

• Persistence: Redis can persist data to disk in case of downtime.
• Data Sharding: Redis clusters can shard data to multiple nodes to improve throughput and processing power.
• Read-write separation: Applications can direct read requests to slave nodes, further improving availability.

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