Messages vs Streams

Messages and Streams are often used interchange‐ably but a subtle but essential differences exists between the two. A message is raw data communicated across two or more systems. Messages are discrete and singular signals in an event-driven system.

By contrast, a stream is an append-only log of event records. As events occur, streams are accumulated in an ordered sequence, using a timestamp or an ID to record events order. Streams are used when you need to analyze what happened over many events. Because of the append-only nature of streams, records in a stream are persisted over a long retention window—often weeks or months—allowing for complex operations on records such as aggregations on multiple records or the ability to rewind to a point in time within the stream.