Design the delivery path for a video streaming service. Players fetch a manifest, then pull two-second video segments one after another for hours; a transcode pipeline publishes new segments as titles are ingested.
The catalog is a petabyte and a premiere night peaks in the hundreds of thousands of segment reads per second — numbers that disqualify whole categories of design before you place a box (the image-hosting problem already taught that half). Segments are immutable once published, so 95% of reads are cacheable and the edge will do most of the serving. That part is a given.
The actual engineering is arithmetic on what the edge does NOT absorb. Five percent of a premiere flood is still tens of thousands of reads per second, it all lands on whatever you call an origin, and origin storage serves blobs slowly. Size that fleet for a normal evening and the premiere will find you; size it for the premiere and the bill barely moves — which is its own lesson about where the money in a CDN system actually lives.