NOTE
Publish–Subscribe Pattern
Decoupling event publishers and subscribers while handling delivery, ordering, replay, and failure semantics.
This is a historical learning note and may contain outdated or incomplete understanding.
In publish–subscribe, producers publish messages/events to a channel or topic and subscribers receive matching publications without the producer directly invoking each consumer.
The pattern reduces direct coupling but does not remove delivery semantics. Define whether delivery is durable, replayable, ordered, at-most-once or at-least-once, and how subscriber failures are retried or isolated. Consumers should be idempotent when duplicates are possible.