Layer 3 · Go deeper · 7 min
Go deeper
Size it, build it, then make the calls an interviewer will push you on.
Back of the envelope
Size it up
Tap through each step of the arithmetic.
Search traffic goes 10× on sale day. Does splitting it out save CPU?
How many possible conversations do 8, 50 and 150 people have?
Build-up · 6 steps
Split one module out, the safe way
A checkout monolith, Orders, Stock and Payments, goes from tangle to “a modular monolith plus one service”, a valid end state. Watch what each move buys and costs.
Step 1 of 6
One deployable, no seams
Orders, Stock and Payments build and deploy as one unit over one database. Calls cost nanoseconds and checkout is one transaction, but any module can reach into another, so every change ripples everywhere.
4 interview moments
You’re the candidate
The interviewer pushes on the hard parts. Pick an approach and see how it holds up.
Deep dive 1 of 4
Interviewer
“You’re building a new food delivery app with one team. How do you structure it?”
Your move. Pick an approach:
Deep dive 3 of 4
Interviewer
“Each of your 140+ event destinations has its own service, queue and repo. Three engineers spend most of their time keeping it alive. Now what?”
You split them so one slow destination couldn’t delay everyone on a shared queue.
Your move. Pick an approach:
Deep dive 4 of 4
Interviewer
“Your checkout request calls ten services one after another, each 99.9% available, failing independently. What do you change?”
Your move. Pick an approach: