Well, I've worked on two now... once was self-hosted by a large services company, which has its' own data centers and redundant connections, it also handles a significant portion of DNS for the internet (for good or bad). It worked for them, but was painful.. Getting new servers up was months of work.
I'm working at another service company expecting to clear 5M requests/day with bursts close to what you're talking about several times a year. We've had so much pain managing colocated servers, we can't justify the cost of 3 full data centers for just our load, that doesn't make sense. We're currently moving to a cloud provider to be able to scale out better when peaks really spike.
We had a customer that wanted to do several million requests in a 15 minute window, and can't currently handle that... We're restructuring/refactoring so that we can.
It may not be sustained, but getting 330k requests/second in bursts is a different way to think about problems than anything less than 1k/second, which many servers can hit without a sweat, and why I'd be more inclined to push for mid-level VPS like DO or Linode in those cases. Depends on need and expected growth.
Shouldn't be anything incredibly high. I haven't seen any recent traffic info for HN, but a couple of years ago dang posted some numbers here: https://news.ycombinator.com/item?id=9219581
So at that point it was 2.6M views per day, which means HN itself was getting about 30 views per second. If you look at the 200k uniques instead (which might make more sense since any individual person will probably only click through once), that's about 2 unique visitors per second. So even if HN has grown a ton in the time since that post, I'd be surprised if it sent more than about 5 hits/second to anything.
Hah, the fact that HN itself is a single server (behind Cloudflare, these days) should be enough proof that anything linked to by HN is unlikely to need more than a single server behind a caching CDN.
Well, let's also differentiate computationally-intensive hits (e.g., users adding things to a shopping cart, requests to list Pokemon in the area, etc.) from hits to a home page, which should be static or at least cached aggressively. 150,000 index.htmls per second and 150,000 database writes per second are very different.
I used to run a university web hosting platform that currently has, I think, five web server VMs on about as many physical machines, two physical machines for load balancing, and two physical MySQL servers in active/passive replication (i.e., only one gets either reads or writes). We hit the front page of HN fairly frequently—for instance, we host mosh.org—and it hasn't really been a problem. I remember getting paged in ... 2009 or so? ... when a particular website in WordPress got to the front page of Reddit, but we had fewer machines then, and also I think we had not deployed FastCGI for PHP at that point (for complicated shared-hosting reasons), so each WordPress page load was its own PHP process via CGI. If you're optimizing for performance, even if you want to stay on WordPress, step one is to not use plain CGI and step two is to do one of the myriad things you're supposed to do for WordPress caching.
In any case, a handful of physical machines will handle being on the front page of HN just fine. If you're doing something where you have an extremely computationally-intensive process on the first page load and you're worried you might hit HN but you might not, put it on cloud and set up autoscaling, but other than that it probably doesn't make sense. If you know you won't scale too much—and a static site on the front page of HN isn't too much—chances are that your usage is so low that you're paying a premium for the unused ability to scale and you should just pay for two cheap VPSes, and if you know you will scale (e.g., you have a large fixed workload), again you're paying a premium for the unused ability to scale down, and you should just invest in a datacenter and save in the long term.
All that said, if you've got a static site, by all means stick it on a CDN, which I think is a perfectly defensible use of cloud for sites of all sizes.
I don't remember exactly, but not that many, maybe a couple thousand concurrent users. My brother's webapp has hit the front page of Reddit a few times, but a single dedicated machine was more than enough to handle that.
(And are they not better served by buying and operating their own datacenters?)