The HLD interviewThe picker
“Live”, “tatkal”, “wallet”. How does the prompt tell you where to dig?
0%
Page 17
More questions.
Core conceptsThe front door
You put two servers behind one load balancer. What did you build?
0%
Networking and APIsNo timeout
A service dies in 4 seconds with its CPU idle. What ran out?
0%
Data and storageSnapshots
A 20-minute report reads every UPI wallet. Why don’t payments freeze?
0%
Caching fundamentalsThe herd
A key expires. Why do 4,000 identical queries hit your database?
0%
Messaging and streamsOrdering
Why would a payment show “pending” after the money moved?
0%
Distributed coordinationPartitions
A network split cuts your 10-node cluster into 6 and 4. Who’s dead?
0%
Running in productionThe idea
How can one slow tandoor stop every dosa in the kitchen?
0%
Why is it slow? Performance anti-patternsDetect it
CPU at 5%, yet every request is timing out. What’s going on?
0%
SecurityDevice grant
How does a smart TV with no keyboard sign you in?
0%
Multi-tenant SaaSConfig pushes
Why did one minor rule change take Cloudflare down for 27 minutes?
0%
Architecture stylesRound trips
Why does one HTTPS request from Pune to US East wait 603 ms?
0%
System design trade-offsCausal
Why did the reply show up before the question it answered?
0%
Key technologiesUploads
How does a 2 GB video reach S3 without touching your servers?
0%
Common patternsRead-your-writes
You saved your new address. Why does the page still show the old one?
0%
InfrastructureFailure
Redis just stalled. Should your API let everyone in, or no one?
0%
Search & discoveryCricket final
Assume 40,000 fans a second search “ind vs aus”. What actually gets hot?
0%
Storage & mediaEncoding
Why does a car chase get more bits than a landscape?
0%
Social & feedsFan-out
One post becomes 200 writes. Why is that the cheap option?
0%
Real-time & collaborationGlobal
Two cousins in one Toronto house. Why might their voices travel via India?
0%
Location & mapsPub/sub
Asha takes a step. Which of 200 servers should hear about it?
0%
E-commerce & bookingIsolation
How did one shop’s flash sale take down its neighbours on Shopify?
0%
Payments & fintechTamper evidence
A superuser quietly edits an old entry. How would anyone ever know?
0%
Data, analytics & monitoringBeacons
You switch apps, then swipe the browser away. Who sends the last event?
0%
Developer platformsOIDC
How does a deploy job reach the cloud with no stored keys?
0%
AI & LLM systemsFailures
A 1,024-GPU run breaks about every two days. How does it finish?
0%