Prep RoomSign inStart free
Code RoomMulti-CDN steering and failover
HardPrep Room Coding #3608

Multi-CDN steering and failover

System designStorage & CDNReliability & on-callSenior–Staff~45 min

Design the multi-CDN steering and failover system for a streaming service that delivers VOD + live across three commercial CDNs plus its own edge. You must route each viewer's segment requests to the CDN that's currently fastest/cheapest for them, detect a CDN degrading (a region browning out, error rate climbing) within seconds, and shift traffic away — all without breaking in-flight playback sessions or stampeding a healthy CDN. Scale: tens of millions of concurrent streams, a single live event can spike one region 10x.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.

Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
0:00
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.