Suggest an editImprove this articleRefine the answer for “What does Redis Cluster consist of?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)Redis Cluster consists of master nodes (hold the data, each responsible for its own range of the 16384 hash slots), replica nodes (a backup, automatically promoted to master on failure), the hash-slot mechanism (`CRC16(key) % 16384`), and a Gossip protocol, through which nodes exchange state with no central coordinator. **Key point:** client drivers need to understand `MOVED` and `ASK` responses, so they can automatically redirect to the right master when a key lives on a different node; the whole system self-coordinates through Gossip.Shown above the full answer for quick recall.Answer (EN)Image**Redis Cluster** consists of several types of nodes and support mechanisms that together provide scaling, fault tolerance, and automatic recovery. ### 1. Master nodes - The main working nodes, which **hold the data**. - Every master is responsible for a specific range of **hash slots** (out of the 16384 possible). - They handle **writes and reads**. Example: ```javascript master1 → slots 0-5460 master2 → slots 5461-10922 master3 → slots 10923-16383 ``` If a master fails, one of its replicas automatically becomes the new master. ### 2. Replica nodes - Copy a specific master's data and act as a **backup**. - Normally they only read data, but on their master's failure, they perform **automatic failover** and become the new master. - Replication is asynchronous. Example: ```javascript master1 → replica1 master2 → replica2 master3 → replica3 ``` ### 3. The data-distribution mechanism, hash slots - Every Redis Cluster key is distributed across **16384 hash slots**. - Every master is responsible for a portion of those slots. - The distribution is computed with this formula: ```javascript CRC16(key) % 16384 ``` - That lets the cluster know exactly where every key is stored. ### 4. The Gossip protocol (how nodes interact) - The cluster's nodes exchange state with each other through a **built-in Gossip protocol**. - Every node regularly tells the others: - what it is (master/replica), - which slots it serves, - which nodes are available or unavailable. That lets Redis Cluster operate **with no central managing server**, the system self-coordinates. ### 5. The failover mechanism - If a master is unreachable, its replica gets confirmation from a majority of the other masters and **becomes the new master**. - The other nodes learn about it through Gossip and update their metadata. ### 6. Cluster-aware clients - Redis clients (drivers) need to understand `MOVED` and `ASK` messages. - When a key lives on a different node, the client is automatically redirected to the right master. ### Redis Cluster's overall structure ```javascript master1 → replica1 master2 → replica2 master3 → replica3 ↓ (every node is connected via Gossip) ↓ data is distributed across 16384 slots ``` **Summary:** Redis Cluster consists of: 1. Several **master nodes**, holding the data. 2. Their **replicas**, providing fault tolerance. 3. The **hash-slot mechanism**, distributing the keys. 4. The **Gossip protocol**, connecting every node. 5. **Failover and client-side routing**, keeping the system running continuously and letting it scale.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.