Kafka is a distributed event streaming platform. It guarantees ordering only within a partition. You must use the same Partition Key for related events (e.g., same UserID) to ensure they are processed sequentially.

Unbuffered channels block until both sender and receiver are ready (synchronous). Buffered channels allow sending data without immediate receiving up to a limit (asynchronous), useful for rate limiting or batching.

Backpressure prevents system overwhelm when the consumer cannot keep up with the producer. Mechanisms include dropping messages, buffering (queueing), or rejecting new work (rate limiting).