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:
```typescript
import { createCluster } from 'redis';
const cluster = createCluster({
rootNodes: [
{
url: 'redis://10.0.0.1:30001'
},
{
url: 'redis://10.0.0.2:30002'
}
]
});
cluster.on('error', (err) => console.log('Redis Cluster Error', err));
await cluster.connect();
await cluster.set('key', 'value');
const value = await cluster.get('key');
```
## `createCluster` configuration
> See the [client configuration](./client-configuration.md) 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](#node-address-map) |
| modules | | Included [Redis Modules](../README.md#packages) |
| scripts | | Script definitions (see [Lua Scripts](../README.md#lua-scripts)) |
| functions | | Function definitions (see [Functions](../README.md#functions)) |
## 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.
```javascript
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.
```javascript
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](https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/accessing-elasticache.html) for more information on that.
## Command Routing
### Commands that operate on Redis Keys
Commands such as `GET`, `SET`, etc. are routed by the first key, for instance `MGET 1 2 3` will be routed by the key `1`.
### [Server Commands](https://redis.io/commands#server)
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. This client sends these commands to a random node in order to spread the load across the cluster.