How to Expand a Redis Cluster: Adding Nodes, Resharding Slots, and Configuring Cross‑Replication
This guide explains how to scale a Redis cluster by deploying new nodes, using redis‑trib to add them, redistributing hash slots through resharding, and setting up a four‑master four‑slave cross‑replication topology while verifying cluster health with CLI commands.
Redis clusters store data in memory and can be scaled by adding new nodes and redistributing hash slots.
1. Deploy Redis on the new server, then use
redis-trib.rb add-node new_ip:new_port existing_ip:existing_portto join the node to the cluster.
2. Install Ruby on any existing node to run the redis‑trib tool.
3. Reshard slots using redis-trib.rb reshard <ip>:<port>, choosing the number of slots (e.g., 4096) and the target node ID, and optionally selecting “all” as source nodes.
4. Verify the slot distribution with redis-cli -h <ip> -p <port> cluster nodes and ensure each node holds the expected 4096 slots.
5. Configure a four‑master four‑slave cross‑replication topology by issuing CLUSTER REPLICATE <master_id> on the appropriate slave nodes.
6. Check cluster health with redis-cli -h <ip> -p <port> cluster info, confirming cluster_state:ok and all slots assigned.
Throughout the process, screenshots illustrate the before/after architecture and command‑line interactions.
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