A colleague says "we need Kafka." What do you ask?

Answer it out loud before you open anything. The value of the flags below is in comparing them to what you actually said — including whether you asked who uses it before naming what you would build it with.

The situation behind the question

In a design review for the online store, a senior colleague says checkout should publish an event to Kafka so that email, analytics and the warehouse can consume it. The store currently sends the confirmation email inside the checkout request and has a few hundred orders a day (illustrative). The colleague has run Kafka before and is confident.

React to this

Say what you would question, what you would keep, and what you would need to know first.

The decomposition, the proposal, or the transcript as it stands

Design review comment (illustrative)

  "Checkout should publish an OrderPaid event to Kafka. Email, analytics
   and the warehouse each get a consumer group. This decouples everything
   and we get replay for free. I've run Kafka at my last two companies;
   I can have the cluster up this week."

  Current state: checkout calls sendEmail() inline; analytics is a nightly
  SQL job; the warehouse gets a CSV export every morning.
  Orders per day: a few hundred (illustrative).
  Incidents in the last quarter attributed to email: 1 (email API slow,
  checkout timed out).

What it is really testing

Whether the candidate can climb the why ladder — from a named technology to the requirement underneath it — without either rubber-stamping the senior or dismissing the tool. The device is "find out what you need", not "big tools are wrong".

Where the move is taught

First Principles lessons →Stuck because X → do Y →Where to start →Practice challenges →