Concepts

In JetStream the configuration for storing messages is defined separately from how they are consumed. Storage is defined in a Stream and consuming messages is defined by multiple Consumers.

We’ll discuss these 2 subjects in the context of this architecture.

While this is an incomplete architecture it does show a number of key points:

• Many related subjects are stored in a Stream
• Consumers can have different modes of operation and receive just subsets of the messages
• Multiple Acknowledgement modes are supported

A new order arrives on ORDERS.received, gets sent to the NEW Consumer who, on success, will create a new message on ORDERS.processed. The ORDERS.processed message again enters the Stream where a DISPATCH Consumer receives it and once processed it will create an ORDERS.completed message which will again enter the Stream. These operations are all pull based meaning they are work queues and can scale horizontally. All require acknowledged delivery ensuring no order is missed.

All messages are delivered to a MONITOR Consumer without any acknowledgement and using Pub/Sub semantics - they are pushed to the monitor.

As messages are acknowledged to the NEW and DISPATCH Consumers, a percentage of them are Sampled and messages indicating redelivery counts, ack delays and more, are delivered to the monitoring system.