Lesson 17 · Senior NATS practice

Reviewing NATS and JetStream designs like a senior engineer

How to judge whether a NATS/JetStream design is truthful about delivery, tenancy safety, consumer shape, and operational trade-offs.

Your win: review NATS and JetStream designs for hidden trade-offs, weak assumptions, and overclaimed guarantees instead of stopping at “it uses JetStream.”

How to get the most out of this page

This page is not mainly about learning new NATS features. It is about learning how to read a proposal, a PR, or a system diagram with sharper questions. If you use it that way, it becomes one of the most practical pages in the whole course.

The important move is simple: stop asking whether the design uses the right vocabulary, and start asking whether the guarantees being implied are actually true in the implementation.

What strong review comments usually target

A design can mention JetStream, durable consumers, explicit ack, and queue groups — and still be weak. Senior review is the skill of checking whether those words connect to real guarantees in the code path.

• subject families that are too broad or semantically mixed
• queue-group scaling claims that ignore handler cost or backpressure
• replay assumptions that ignore stale-event or idempotency boundaries
• failure flows that talk about retry but never explain poison handling or visibility
• async handling paths that forget to preserve tenant or trace context safely

The best review comments make the hidden contract explicit. They turn “JetStream handles it” into “which exact behavior are we relying on, and where is that behavior enforced?”

Check yourself (from memory)

Sources. Repo NATS map; existing NATS lessons; official JetStream docs.