Can you share a bit more about the architecture and stack? And a few more details such as Roughly how many TPS do you serve from this setup? Does it scale well? Are response times consistent?
No problem with scaling.
Stack Overflow runs on a single machine. Use a fast compiled language and a simple stack. No need in $6k/mo AWS bills which are the fashion these days.
https://nickcraver.com/blog/2013/11/22/what-it-takes-to-run-...
2 - still, in 2013 is not 1 server. It's also more than you said now ( add a tag engine server, elastic search, redis, load balancer) and an insane amount of memory on a lot of those servers. Even then, the stack exchange network is more than that.
Saying 1 server, as you did, is not correct and it never was :)
Having thousands of users is a meaningless metric for web operations. Are those concurrent users? Are those read/write heavy users? Are those mixed usage users? There are a lot of qualifiers that need to be attached to that question to allow any meaningful discourse.
Always looking to optimize on cost for AWS. But it's a tradeoff of something or the other. Light Sail sounds like a great solution for some use-cases though.
We run this for a Global/North American airline and easily hit 1k TPS just on API and event processing traffic. The spikes can show up anywhere in the multitude of processes due to various business events (high reservation traffic to irregular operations due to weather, pandemics etc.) Performance and reliability wise, serverless has been a very predictable consistent experience. Costs are another story.