[user5994461]

Also disagree with you based on experience ;)

patio11 blog is HTTP only but this blog is HTTPS.

HTTPS without keepalive is likely to kill any cheap VPS, establishing HTTPS connection is intensive.

That being said, the core of the issue is that they should use nginx (or apache in mpm-events). And they should have cloudflare.

[patio11]

establishing HTTPS connection is intensive

More intensive than adding numbers together, sure, but computers are pretty fast. If you're doing 100k connections a second you might have to give some thought to that. Meanwhile, if you have KeepAlive on, 2~5 clients per second will kill you.

[carbocation]

I guess we're going to just wait here until OP delivers the answer for why the machine couldn't answer enough requests :)