Layer 3 · Go deeper · 8 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.
How many app servers when tatkal booking opens at 10:00?
At that peak, how much load reaches the database?
Two million apps reconnect after a deploy. How hard do they hit?
Build-up · 5 steps
Grow one server into tiers
The usual path for scaling the server side, one step at a time. Watch where the limit moves.
Step 1 of 5
One box does everything
One server runs the app and the database. It’s the simplest start, and also the single point of failure: when it stops, every client stops.
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
“Your booking API runs on several servers behind a load balancer. Where do logged-in users’ sessions live?”
Your move. Pick an approach:
Deep dive 2 of 4
Interviewer
“A desktop billing app sends SQL straight to a database and works for 50 trusted users on a LAN. How do you put it online?”
Your move. Pick an approach:
Deep dive 3 of 4
Interviewer
“Field-sales staff take orders in villages with patchy coverage. What kind of client do you build?”
Your move. Pick an approach:
Deep dive 4 of 4
Interviewer
“A deploy restarts your servers and two million connected apps lose their connection. How should they reconnect?”
Your move. Pick an approach: