As mentioned in someone else's post, it is PortableApps.com. I left it off as I didn't want to be self promotional in the reference. Mine is far from the largest Drupal site, so other sites like Weather.com and The Onion have done more with large-scale scaling in terms of multiple servers and the like. Personally, for PortableApps.com, I've used Advanced CSS/JS Aggregation [1] and LABjs [2] to help quite a bit in terms of caching along with offloading images and static scripts to a CDN (MaxCDN in our case). Moving the MySQL data from a standard server-based instance to Rackspace's Cloud Database instance and the Drupal install from a dedicated server to a cloud server that can be up/downgraded helped as well. All while keeping costs to about the same as the old single dedicated server.
> Mine is far from the largest Drupal site, so other sites like Weather.com and The Onion have done more with large-scale scaling in terms of multiple servers and the like
Don't forget https://www.whitehouse.gov - it's a Drupal 7 site, and I imagine it gets a fair amount of traffic.
Quite true. They did have one of the largest Drupal sites for a while. I'd wager that the articles that explored how they did it would be a little outdated now as I think they were on Drupal 6 when they switched platforms.
There are a lot of great posts and case studies about weather.com, which is a solid example of drupal in a high performance environment.
Performance has been a specialty for me in my own drupal career. Drupal 8 is a whole new ballgame, though. Cache tags are built in from the ground up, and the page render/caching engine is built to mimic a reverse proxy. Rasmus Lerdorf (creator of the PHP language) benchmarked a pre release of drupal 8 at >2500 page views per second with 20 concurrents.
That's it. And I run Drupal on my personal site as well as you noted. I have a handful of other Drupal sites and a couple WordPress sites I help with, too. I'll probably upgrade my personal site first and my internal test sites running on local server instances to play with.
Do you have any blog posts on how you manage to scale with drupal? Have you considered alternative solutions?