interviewed for a staff-level SWE role at lululemon earlier this year. the system design round was 60 minutes and easily the most interesting design interview i've had outside of FAANG. figured i'd share what the format looked like since most people seem to go in blind.
the prompt: they gave me a vague starting point: design the product catalog and availability service for a major retail site that needs to handle seasonal spikes (think Black Friday, new seasonal drops). they didn't say "design Amazon" they said design it for us specifically, which actually made it more interesting.
what they dug into: caching strategy for product availability (stock changes fast, stale reads are costly) handling inventory consistency when multiple users are checking out simultaneously how you'd partition data at the catalog scale they operate at (they have hundreds of thousands of SKUs across colors/sizes) CDN strategy for product images and how you'd manage invalidation
notably they did NOT do a generic "design Twitter" style prompt. everything was grounded in retail/e-commerce context. if you've never thought about SKU management, inventory reservation patterns, or the read-heavy vs write-heavy split in retail systems, read up before you go in.
what seemed to matter: identifying trade-offs out loud before they asked. they pushed back deliberately to see if i'd defend or revise my choices. not pretending i'd build everything from scratch. they appreciated when i said "here i'd use an off-the-shelf search index and here's how i'd configure it" keeping the whiteboard diagram clean and iterating on it
the interviewer was a senior engineer, sharp, clearly had strong opinions. felt collaborative rather than adversarial but they definitely probed weak spots.
for prep: if you've done FAANG-style system design you'll find this slightly less algorithmically intense and more operationally focused. retail domain knowledge is a real differentiator here. read about inventory management systems, flash sale architectures, and CDN edge caching before you walk in.
one thing i didn't expect: they asked how i'd monitor and alert on the service in production. reliability thinking matters to them.