Java: Message Brokers (Kafka)

Kafka uses persistent storage and replication to ensure messages are delivered even if consumers are offline.

Kafka stores messages on disk in a fault-tolerant manner. Each message is written to a partition and replicated across multiple brokers. If a consumer is offline, Kafka retains the messages until the consumer is ready to process them. This ensures no data is lost during temporary outages. For example, if a payment processing service is down, messages related to transactions are retained by Kafka for later processing.