NATS JetStream

JetStream is NATS's built-in persistence engine enabling message storage and replay. Unlike Core NATS (which requires active subscriptions), JetStream captures messages and replays them to consumers as needed.

Core Mental Model

Streams store messages. Consumers read them.

• Streams = append-only logs that capture messages by subject
• Consumers = cursors/views into streams that track position and can replay

This separation allows flexible deployment: one stream can have many consumers with different starting points, filters, and delivery patterns.

When to Use JetStream