Does Redis ensure reliable message delivery?

Redis itself does not guarantee reliable message delivery because it is an in-memory storage that can be used as a message broker but without built-in acknowledgment and retry mechanisms.

In Redis Pub/Sub, messages are sent to subscribers, but if the subscriber is not active at the moment of publication, it will miss the message. There is no guarantee of delivery and message persistence.

For more reliable delivery, Redis data structures like lists (using LPUSH and BRPOP commands) can be used to implement message queues, where consumers process messages and acknowledge their processing, increasing reliability.

Alternatively, Redis Streams support message storage, acknowledgment, and consumer reading with position tracking.

Thus, for reliable message delivery in Redis, it is recommended to use Redis Streams or list-based queues rather than simple Pub/Sub.