A websocket is a persistent communication channel open between a server (based on Node.js) and a client (using a web browser). Messages can be sent bidirectionally using this method, making websockets useful for notifications, chat clients, and other content updates that should appear asynchronously from a traditional page load.
Differences between Node.js and PHP
With PHP, each new Drupal request starts a new PHP process, which must be terminated when the request is completed. For a websocket to function in a PHP application, the PHP process must always remain open and waiting for connections instead of terminating. Unfortunately, because Cloud Platform has a time limit for PHP connections this approach is not possible.
As a comparison, due to how Node.js is designed implementing a websocket is trivial, and has valid use cases with a decoupled Drupal installation. For example, if the websocket server detects a change in the content managed by Drupal, it pushes those content updates to all connected clients. Cloud Platform supports implementing a websocket server using Node.js.
Note
Acquia strongly recommends that you test your websocket-based applications before deployment. Concurrent websocket connection numbers may vary based on server size and application.
Websocket use cases
One websocket use case example is having an application that needs real-time updates (such as a sports scoreboard or a live text feed on a news website). When the websocket server detects a content change in Drupal, it pushes updates of your Drupal-managed content to all connected clients.
Although you could develop this application only using Drupal, doing so would require each client to poll your web infrastructure on a timed basis, drastically increasing your website’s traffic. As an example, if 100,000 visitors were viewing live updates of a game on your website, and each visitor’s browser polled your website for traffic every 10 seconds, Drupal would receive approximately 600,000 requests per minute. The only way a traditional Drupal website could handle that much traffic is by using caching, but this approach would require you to clear the cache every time a score changed during the game.
By developing this application using a Node.js websocket server, those same 100,000 clients would each open a websocket, and from that time forward, only Node.js would determine when to make a Drupal request. If Node.js contacted Drupal every 10 seconds for updates, those six requests per minute would then be pushed to all 100,000 website visitors. Since traffic to the infrastructure would be low those six requests could remain uncached, which would allow Drupal to perform normally.
Configuring websockets
Websockets require a specific path (such as /_socket) on Cloud Platform.
Websockets also require a path, which can be used by exposing a port for
your application. Acquia exposes a port through the process.env.PORT
variable.
Use of this port for websockets depends on the Node.js library that the application is using. For specific information about many common websocket libraries for Node.js, see Which websocket library to use with Node.js? on Stack Overflow.
Using socket.io
To use socket.io in an application hosted on Acquia Cloud, complete the following steps:
Set the listening port using
process.env.PORT.Set the socket path to
'/_socket'.Set the transport for the socket to
"['websocket']".Add the following required parameters to your application:
Server: var server = require('http').createServer(app); var io = require('socket.io')(server, { path: '/_socket' }); var port = process.env.PORT || 3000; io.set('transports', ['websocket']); Client: var socket = io('example.com', { path: '/_socket', transports: ['websocket'] });``