Module 5 - Design scenarios

Defend a system design

Open-ended prompts that mirror the design round. Each one comes with the justification pressure an interviewer applies, a rubric, and a model discussion of the trade-offs.

core
Design a BFF over six flaky upstreams under a 300ms budget
Six upstreams, each slow or failing in its own way, and one 300ms budget for the mobile app. Decide what is mandatory, what can degrade, and what you are willing to serve from cache.
core
Design a streaming export for 10-million-row reports
Ship a 3GB CSV built from 10 million database rows, with progress, cancellation, and resume, from a process that never holds more than a few megabytes of it at once.
intro
Design zero-downtime deploys for a fleet with long-lived connections
Ship twice a day to a fleet holding 15,000 WebSockets per instance, drop no request, and keep 200,000 clients from reconnecting in the same second.
hard
Design a background job system with retries, priority tiers, and a dead-letter path
At-least-once execution at 5,000 jobs per second, three priority tiers, and a worker that dies mid-job. Design the system that never loses work and reports its state honestly.
hard
Design a log ingestion tier that absorbs 100k events per second
Absorb 100,000 events a second with 256MB per instance and a 50ms ack budget. Account for every dropped event in a budget you control instead of discovering the loss during an incident.
core
Design realtime fan-out to 200,000 connected clients
Push live scores and presence to 200,000 open connections across a fleet, and decide what happens to a client on hotel wifi that cannot keep up with a goal burst.
core
Design a resumable upload pipeline with scan and transcode stages
Accept 50GB uploads over flaky connections, scan and transcode them, and hold every Node process flat at half a gigabyte the whole time.
hard
Design webhook delivery for 50,000 customer endpoints
Deliver signed events to 50,000 endpoints you do not control. Hold per-endpoint ordering, and stay up when one customer's server times out for six hours.