CourseAI System Design: The Complete Course · Module 4: Architecture Selection · part 30 of 107
Part 30 · Module 4: Architecture Selection

Lesson 2: Choosing an architecture by the numbers

26 min read·
Module 4 · Lesson 2 · About 50 minutes · Needs: Module 1 lesson 3 (the posture and one-way doors), Module 3 lesson 2 (token arithmetic), and Python functions

The situation

Week 4, Monday 23 November 2026. Joel still wants Cases version 2 to be a planner agent, one agent per back-office system and a model fine-tuned on old tickets. Gareth asks his usual question: "Why not a workflow?"

You answer with one request. A Tallis Retail Group employee sends Cases: "My laptop screen is cracked, please arrange a replacement." Before any tool runs, something must decide which job this is: a rule, a classifier or a model call. Each choice is priced on that request first.

THE CHOICE Three ways to route one request My laptop screen is cracked rule $0, microseconds classifier $0, 0.14 ms model call per token, round trip device_fault workflow
One Cases request (amber, a user's text) can be routed by a rule, a classifier (blue, Northdesk's code) or a model call (amber); the lesson prices each before choosing.

The rest of this course is yours to keep

This course is bought on its own, once, and stays readable afterwards, including the parts added to it later.

Buy this course · ₹399See what is inside

Or open everything with a plan