A catalog page that's fast for ten users can fall over for ten thousand. A deep-dive on the layers of caching that keep it fast — fragment caching, HTTP/CDN caching, low-level caching — and the hard part: invalidation and stampedes.
Selling across countries means translating not just your interface but your data, your URLs, your formats, and your SEO. A deep-dive on Rails i18n at scale — locale files, translated content, locale routing, and the traps.
A product catalog is mostly images, and naive image handling will sink it. A deep-dive on building an image pipeline that scales — keeping originals, generating variants in the background, offloading to a CDN, and not melting your web servers.
Selling in more than one currency sounds like a display problem and turns out to be a data-modelling one. A deep-dive on representing money correctly, storing prices across currencies, exchange rates, rounding, and the mistakes that cost real money.