Pub-sub

How this question breaks down

1. 1TopicsCore20 minPublishers write each event once to a named topic, and every subscription attached to it gets its own copy and its own record of what has been read.
2. 2Fan-outCore22 minTurning one published message into thousands or millions of deliveries: where the copies are made, what each strategy costs in storage and bandwidth, and how to stop one slow receiver from hurting the rest.
3. 3PushCore26 minHow an event on the broker reaches a browser or app that is online right now, through the connection the client keeps open, the gateway that holds it, and what happens when that connection drops.

Work through the parts in order and you’ve covered the full design. Each part is one topic.