They do have a pretty complex infra with redundancy, extensive caching, the whole works. But I think they use a relatively boring, reliable stack throughout. It doesn't look like they run a lot of GARTNER MAGIC QUADRANT Cloud Solutions to Supercharge™ their web-scale data blazingly.
On the plus side solid stable software can run for decades without incidents, as long as the hardware is willing. The main negative is that it's not as Supercharged™ as the latest cloud product with a 99.9% SLA, which itself relies on 5 other internal microservices with 99.9% SLA each.