Pub/ Sub in Redis

How to subscribe to a channel 

With the SUBSCRIBE command, a client can subscribe to any channel.

This command accepts the channel names that the client wishes to subscribe to.

Syntax

SUBSCRIBE channel_name-1 channel_name-2

A channel is instantly formed and made available to publishers when a client subscribes to it.

Example

SUBSCRIBE eurusd-tick

Redis will return the operation, the channel name(s), and the number of subscribed channels.

Output

1. "subscribe"
2. "eurusd-tick"
3. (integer) 1

How to publish messages to a channel

Using the PUBLISH command, a publisher can deliver messages across any channel with at least one subscriber. As an input, this command accepts the message to send.

Continuing with the previous example, create a new command line (or a new tab if your system allows it) and enter the Redis CLI.

If you're using Docker, enter the following command.

Example

docker exec -it image_name sh

This client will be used to send messages to those who have previously subscribed to 'eurusd-tick.'

Syntax

PUBLISH channel_name

Example

PUBLISH eurusd-tick 1.17057

We can see that the message was received by switching to the subscriber client.

Output

1. "message"
2. "eurusd-tick"
3. "1.17057"

Frequently Asked Questions

1. What is the purpose of Redis Pubsub?
   Redis may be used as a Publisher/Subscriber platform in addition to data storage. Publishers can send messages to any number of subscribers on a channel using this pattern.
    
2. What is the publish-subscribe pattern?
   Publish–subscribe is a communications pattern in which message senders, known as publishers, do not design messages to be delivered directly to specific receivers, known as subscribers, but instead, the group published messages into classes without knowing which subscribers, if any, may exist.
    
3. What exactly is a Kafka pub/sub?
   Kafka is a Pub-sub and queue-based messaging system that is extremely fast, reliable, persistent, fault-tolerant, and has zero downtime. Furthermore, producers deliver the message to a subject, and the consumer may choose from various message systems.
    
4. Is it possible to replace Kafka with the Redis stream?
   Redis streams are extremely similar to Kafka in terms of functionality. Unlike Pub/Sub, when messages are digested, they are not deleted from the stream. Redis streams may be consumed in two ways: blocking and nonblocking.
    
5. What does it mean to publish in Redis?
   (PUBLISH channel message)
   This command sends a message to the specified channel. Clients can publish to any node in a Redis Cluster. Clients can subscribe to any channel by connecting to any node, and the cluster ensures that published messages are routed as needed.

Conclusion

In this Redis tutorial, we learned how to use the Publish & Subscribe transaction mechanism to send and receive messages. You can explore data types in Redis by clicking here.
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