Scalable WebSocket Solutions for Modern Applications
When building modern applications, scalability is a crucial consideration. Unfortunately, many developers overlook this aspect when implementing WebSockets, leading to issues down the line. In this article, we’ll explore the importance of scalability in WebSocket implementations and provide a comprehensive guide on how to achieve it using NestJS and Redis.
The Problem with Stateless Applications
Traditional backend applications are designed to be stateless, allowing for easy scalability and fault tolerance. However, when introducing WebSockets, this stateless nature is compromised. WebSockets require maintaining a connection state, which can lead to complexities when scaling applications. To overcome this, we’ll leverage Redis as a publish/subscribe mechanism to forward events between instances.
Setting Up a Nest Application
We’ll use the Nest CLI to scaffold our application and Docker with docker-compose to add Redis and Postgres for local development. Our Redis setup will utilize ioredis, providing robust performance and features.
Creating a State of Sockets
To manage WebSocket connections, we’ll implement a socket state service. This service will store sockets in a Map Creating an Adapter Nest’s adapter system enables seamless integration with various libraries. We’ll extend the existing socket.io adapter to track currently open sockets. Our custom adapter will override the create and bindClientConnect methods, setting up a middleware for authentication and registering connection listeners. Creating the Redis Event Propagator With our Redis integration and socket state in place, we’ll create a Redis event propagator service. This service will listen to incoming Redis events and dispatch events to other instances. We’ll define three types of events: emitting to all open connections, emitting to authenticated users, and emitting to a specified user. Listening to Event Dispatches To fully utilize the Nest ecosystem, we’ll create an interceptor that will have access to each socket event response. This interceptor will subscribe to the observable returned by the next.handle() method, allowing us to react to the response without altering it. Working Example Our final step is to create a gateway that listens to incoming events and demonstrates the propagation of events across instances. We’ll use the @UseInterceptors decorator to register the interceptor and simulate a user session with a fake token. Conclusion Scalability is a critical aspect of modern application development. By using NestJS and Redis, we can create scalable WebSocket solutions that meet the demands of growing applications. Remember, making sure our applications are scalable requires a radical change of thinking, but it’s worth it in the long run.