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.
A 12-engineer bill-payments startup: what does the modular monolith score?
Five years on, with 40 teams and steady load: who wins now?
Build-up · 6 steps
Walk the decision flow, question by question
Start simple, and add a style only where a force demands it, for the part of the system that feels the force.
Step 1 of 6
Is the split already clear?
Only a well-understood domain with several teams from day one justifies starting with services, and even then a few coarse ones, split further as the boundaries settle.
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
“A UPI bill-payments app: 12 engineers in 2 teams, a new domain, launch in four months. What do you build?”
Traffic spikes around salary days. Card and UPI data must stay in a small audit scope. You have CI/CD but no tracing.
Your move. Pick an approach:
Deep dive 2 of 4
Interviewer
“Provisioning is slow, deploys are manual and developers never handle incidents. Leadership wants to move to microservices. What do you advise?”
Your move. Pick an approach:
Deep dive 3 of 4
Interviewer
“Your matrix scores the modular monolith 4.10, the monolith and serverless 3.70, microservices 2.50. How do you present it?”
Stakeholders care about time to market, cost, risk and compliance.
Your move. Pick an approach:
Deep dive 4 of 4
Interviewer
“You serve one region’s worth of users at an early stage. An engineer proposes cells now, to limit blast radius. Do you?”
Your move. Pick an approach: