Build a Simple Chat Application with Redis

How do we build a simple chat application using Redis?

The diagram below shows how we can leverage the pub-sub functionality of Redis to develop a chat application.

Stage 1: Connection Initialization

• Steps 1 and 2: Bob opens the chat application. A web socket is established between the client and the server.

• Steps 3 and 4: The pub-sub server establishes several connections to Redis. One connection is used to update the Redis data models and publish messages to a topic. Other connections are used to subscribe and listen to updates for topics.

• Steps 5 and 6: Bob’s client application requires the chat member list and the historical message list. The information is retrieved from Redis and sent to the client application.

• Steps 7 and 8: Since Bob is a new member joining the chat application, a message is published to the “member_add” topic, and as a result, other participants of the chat application can see Bob.

Stage 2: Message Handling

• Step 1: Bob sends a message to Alice in the chat application.

• Step 2: The new chat message is added to Redis SortedSet by calling ‘zadd.’ The chat messages are sorted based on arrival time. The pub-sub server then publishes the chat message to the “messages” topic so subscribers can pick it up.

• Step 3: Alice’s client application receives the chat message from Bob.