Supposed you were asked in an interview "How would you implement Google Search?" How would you answer such a question? There might be resources out there that explain how some pieces in Google are implemented (BigTable, MapReduce, PageRank, ...), but that doesn't exactly fit in an interview.

What overall architecture would you use, and how would you explain this in a 15-30 minute time span?

I would start with explaining how to build a search engine that handles ~ 100k documents, then expand this via sharding to around 50M docs, then perhaps another architectural/technical leap.

This is the 20,000 feet view. What I'd like is the details - how you would actually answer that in an interview. Which data structures would you use. What services/machines is your architecture composed of. What would a typical query latency be? What about failover / split brain issues? Etc...