node-redis/docs/clustering.md

Clustering

Basic Example

Connecting to a cluster is a bit different. Create the client by specifying some (or all) of the nodes in your cluster and then use it like a regular client instance:

import { createCluster } from 'redis';

const cluster = await createCluster({
    rootNodes: [{
      url: 'redis://10.0.0.1:30001'
    }, {
      url: 'redis://10.0.0.2:30002'
    }]
  })
  .on('error', err => console.log('Redis Cluster Error', err))
  .connect();

await cluster.set('key', 'value');
const value = await cluster.get('key');
await cluster.close();

createCluster configuration

See the client configuration page for the rootNodes and defaults configuration schemas.

Property	Default	Description
rootNodes		An array of root nodes that are part of the cluster, which will be used to get the cluster topology. Each element in the array is a client configuration object. There is no need to specify every node in the cluster: 3 should be enough to reliably connect and obtain the cluster configuration from the server
defaults		The default configuration values for every client in the cluster. Use this for example when specifying an ACL user to connect with
useReplicas	false	When true, distribute load by executing readonly commands (such as GET, GEOSEARCH, etc.) across all cluster nodes. When false, only use master nodes
minimizeConnections	false	When true, .connect() will only discover the cluster topology, without actually connecting to all the nodes. Useful for short-term or Pub/Sub-only connections.
maxCommandRedirections	16	The maximum number of times a command will be redirected due to MOVED or ASK errors
nodeAddressMap		Defines the node address mapping
modules		Included Redis Modules
scripts		Script definitions (see Lua Scripts)
functions		Function definitions (see Functions)

Usage

Most redis commands are the same as with individual clients.

Unsupported Redis Commands

If you want to run commands and/or use arguments that Node Redis doesn't know about (yet!) use .sendCommand().

When clustering, sendCommand takes 3 arguments to help with routing to the correct redis node:

• firstKey: the key that is being operated on, or undefined to route to a random node.
• isReadOnly: determines if the command needs to go to the master or may go to a replica.
• args: the command and all arguments (including the key), as an array of strings.

await cluster.sendCommand("key", false, ["SET", "key", "value", "NX"]); // 'OK'

await cluster.sendCommand("key", true, ["HGETALL", "key"]); // ['key1', 'field1', 'key2', 'field2']

Auth with password and username

Specifying the password in the URL or a root node will only affect the connection to that specific node. In case you want to set the password for all the connections being created from a cluster instance, use the defaults option.

createCluster({
  rootNodes: [{
    url: 'redis://10.0.0.1:30001'
  }, {
    url: 'redis://10.0.0.2:30002'
  }],
  defaults: {
    username: 'username',
    password: 'password'
  }
});

Node Address Map

A mapping between the addresses in the cluster (see CLUSTER SHARDS) and the addresses the client should connect to. Useful when the cluster is running on a different network to the client.

const rootNodes = [{
  url: 'external-host-1.io:30001'
}, {
  url: 'external-host-2.io:30002'
}];

// Use either a static mapping:
createCluster({
  rootNodes,
  nodeAddressMap: {
    '10.0.0.1:30001': {
      host: 'external-host.io',
      port: 30001
    },
    '10.0.0.2:30002': {
      host: 'external-host.io',
      port: 30002
    }
  }
});

// or create the mapping dynamically, as a function:
createCluster({
  rootNodes,
  nodeAddressMap(address) {
    const indexOfDash = address.lastIndexOf('-'),
      indexOfDot = address.indexOf('.', indexOfDash),
      indexOfColons = address.indexOf(':', indexOfDot);
    
    return {
      host: `external-host-${address.substring(indexOfDash + 1, indexOfDot)}.io`,
      port: Number(address.substring(indexOfColons + 1))
    };
  }
});

This is a common problem when using ElastiCache. See Accessing ElastiCache from outside AWS for more information on that.

Events

The Node Redis Cluster class extends Node.js’s EventEmitter and emits the following events:

Name	When	Listener arguments
connect	The cluster has successfully connected and is ready to us	No arguments
disconnect	The cluster has disconnected	No arguments
error	The cluster has errored	(error: Error)
node-ready	A cluster node is ready to establish a connection	(node: { host: string, port: number })
node-connect	A cluster node has connected	(node: { host: string, port: number })
node-reconnecting	A cluster node is attempting to reconnect after an error	(node: { host: string, port: number })
node-disconnect	A cluster node has disconnected	(node: { host: string, port: number })
node-error	A cluster node has has errored (usually during TCP connection)	(error: Error, node: { host: string, port: number })

⚠️ You MUST listen to error events. If a cluster doesn't have at least one error listener registered and an error occurs, that error will be thrown and the Node.js process will exit. See the > EventEmitter docs for more details.

Command Routing

Commands that operate on Redis Keys

Commands such as GET, SET, etc. are routed by the first key specified. For example MGET 1 2 3 will be routed by the key 1.

Server Commands

Admin commands such as MEMORY STATS, FLUSHALL, etc. are not attached to the cluster, and must be executed on a specific node via .getSlotMaster().

"Forwarded Commands"

Certain commands (e.g. PUBLISH) are forwarded to other cluster nodes by the Redis server. The client sends these commands to a random node in order to spread the load across the cluster.