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# Socket.IO Redis adapter
The `@socket.io/redis-adapter` package allows broadcasting packets between multiple Socket.IO servers.
<picture>
<source media="(prefers-color-scheme: dark)" srcset="./assets/adapter_dark.png">
<img alt="Diagram of Socket.IO packets forwarded through Redis" src="./assets/adapter.png">
</picture>
**Table of contents**
- [Supported features](#supported-features)
- [Installation](#installation)
- [Compatibility table](#compatibility-table)
- [Usage](#usage)
- [With the `redis` package](#with-the-redis-package)
- [With the `redis` package and a Redis cluster](#with-the-redis-package-and-a-redis-cluster)
- [With the `ioredis` package](#with-the-ioredis-package)
- [With the `ioredis` package and a Redis cluster](#with-the-ioredis-package-and-a-redis-cluster)
- [With Redis sharded Pub/Sub](#with-redis-sharded-pubsub)
- [Options](#options)
- [Default adapter](#default-adapter)
- [Sharded adapter](#sharded-adapter)
- [License](#license)
## Supported features
| Feature | `socket.io` version | Support |
|---------------------------------|---------------------|------------------------------------------------|
| Socket management | `4.0.0` | :white_check_mark: YES (since version `6.1.0`) |
| Inter-server communication | `4.1.0` | :white_check_mark: YES (since version `7.0.0`) |
| Broadcast with acknowledgements | `4.5.0` | :white_check_mark: YES (since version `7.2.0`) |
| Connection state recovery | `4.6.0` | :x: NO |
## Installation
```
npm install @socket.io/redis-adapter
```
## Compatibility table
| Redis Adapter version | Socket.IO server version |
|-----------------------|--------------------------|
| 4.x | 1.x |
| 5.x | 2.x |
| 6.0.x | 3.x |
| 6.1.x | 4.x |
| 7.x and above | 4.3.1 and above |
## Usage
### With the `redis` package
```js
import { createClient } from "redis";
import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
const pubClient = createClient({ url: "redis://localhost:6379" });
const subClient = pubClient.duplicate();
await Promise.all([
pubClient.connect(),
subClient.connect()
]);
const io = new Server({
adapter: createAdapter(pubClient, subClient)
});
io.listen(3000);
```
### With the `redis` package and a Redis cluster
```js
import { createCluster } from "redis";
import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
const pubClient = createCluster({
rootNodes: [
{
url: "redis://localhost:7000",
},
{
url: "redis://localhost:7001",
},
{
url: "redis://localhost:7002",
},
],
});
const subClient = pubClient.duplicate();
await Promise.all([
pubClient.connect(),
subClient.connect()
]);
const io = new Server({
adapter: createAdapter(pubClient, subClient)
});
io.listen(3000);
```
### With the `ioredis` package
```js
import { Redis } from "ioredis";
import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
const pubClient = new Redis();
const subClient = pubClient.duplicate();
const io = new Server({
adapter: createAdapter(pubClient, subClient)
});
io.listen(3000);
```
### With the `ioredis` package and a Redis cluster
```js
import { Cluster } from "ioredis";
import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
const pubClient = new Cluster([
{
host: "localhost",
port: 7000,
},
{
host: "localhost",
port: 7001,
},
{
host: "localhost",
port: 7002,
},
]);
const subClient = pubClient.duplicate();
const io = new Server({
adapter: createAdapter(pubClient, subClient)
});
io.listen(3000);
```
### With Redis sharded Pub/Sub
Sharded Pub/Sub was introduced in Redis 7.0 in order to help scaling the usage of Pub/Sub in cluster mode.
Reference: https://redis.io/docs/interact/pubsub/#sharded-pubsub
A dedicated adapter can be created with the `createShardedAdapter()` method:
```js
import { Server } from "socket.io";
import { createClient } from "redis";
import { createShardedAdapter } from "@socket.io/redis-adapter";
const pubClient = createClient({ host: "localhost", port: 6379 });
const subClient = pubClient.duplicate();
await Promise.all([
pubClient.connect(),
subClient.connect()
]);
const io = new Server({
adapter: createShardedAdapter(pubClient, subClient)
});
io.listen(3000);
```
Minimum requirements:
- Redis 7.0
- [`redis@4.6.0`](https://github.com/redis/node-redis/commit/3b1bad229674b421b2bc6424155b20d4d3e45bd1)
Note: it is not currently possible to use the sharded adapter with the `ioredis` package and a Redis cluster ([reference](https://github.com/luin/ioredis/issues/1759)).
## Options
### Default adapter
| Name | Description | Default value |
|------------------------------------|-------------------------------------------------------------------------------|---------------|
| `key` | The prefix for the Redis Pub/Sub channels. | `socket.io` |
| `requestsTimeout` | After this timeout the adapter will stop waiting from responses to request. | `5_000` |
| `publishOnSpecificResponseChannel` | Whether to publish a response to the channel specific to the requesting node. | `false` |
| `parser` | The parser to use for encoding and decoding messages sent to Redis. | `-` |
### Sharded adapter
| Name | Description | Default value |
|--------------------|-----------------------------------------------------------------------------------------|---------------|
| `channelPrefix` | The prefix for the Redis Pub/Sub channels. | `socket.io` |
| `subscriptionMode` | The subscription mode impacts the number of Redis Pub/Sub channels used by the adapter. | `dynamic` |
## License
[MIT](LICENSE)