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.
What does pushing the same updates cost instead?
Where does each feed strategy pay its cost?
Build-up · 5 steps
A webhook is a hint; pull the truth
Payment results reach you as webhooks. Here is how a push you can’t fully trust becomes a reliable flow.
Step 1 of 5
The gateway pushes
When a payment changes, the gateway pushes an event to your HTTPS endpoint. Return 2xx quickly and do the work afterwards.
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
“Twenty million fans want the live cricket score within seconds. How do you deliver it?”
Your move. Pick an approach:
Deep dive 2 of 4
Interviewer
“Your app learns payment results from a gateway’s webhooks. What makes that reliable?”
Your move. Pick an approach:
Deep dive 3 of 4
Interviewer
“Most accounts have hundreds of followers, but a few have 10 million. How do you build home timelines?”
Your move. Pick an approach:
Deep dive 4 of 4
Interviewer
“50,000 agents poll for config every 60 seconds. You’re about to restart the config service. What do you add first?”
Your move. Pick an approach: