Pub/Sub

Pub/Sub stands for Publish-Subscribe, which is a pattern where messages are not sent directly to specific receivers. Publishers send messages to channels, and subscribers receive these messages if they are listening to a given channel.

Redis supports the Pub/Sub pattern and provides commands to publish messages and subscribe to channels.

Here are some examples of Pub/Sub applications:

• News and weather dashboards
• Chat applications
• Push notifications, such as subway delay alerts
• Remote code execution, similar to what the SaltStack tool supports

The following examples implement a remote command execution system, where a command is sent to a channel and the server that is subscribed to that channel executes the command.

The command PUBLISH sends a message to the Redis channel, and it returns the number of clients that received that message. A message gets lost if there are no clients subscribed to the channel when it comes in.

Create a file called publisher.js in the chapter 4 folder and save...