And you need dev servers. And a way to keep them in sync with production because you can’t just create a branch and provision a bare metal server on the fly. And you need a deployment process to get code from dev through test, UAT and production, and this process is lengthy and fraught because you can’t just fire up a new instance and switch the elastic IP, you actually have to deploy code on the physical machine and make sure there aren’t any configuration differences between your test and prod environments that’ll cause ‘it worked before’ problems. Developer productivity tanks, people are afraid to make changes, any pretence of agile/devops goes out the window and eventually everyone gets sick of the crusty old server and decides a complete rewrite is needed.
While Stack Overflow is popular in the dev world, not so much outside of it. The show they’re only serving 300 req/s. 19 servers to power the entire stack as well. I wouldn’t call this efficient.
Look at Stack Overflow's architecture which stands apart because it was never designed to work in cloud from the beginning: https://stackexchange.com/performance
I'd argue that 90% of the SaaS doesn't have SO's scale. The whole thing would work just fine on a couple of FreeBSD servers running postgres and un-dockerized monolith. Half a rack at most with redundancy and replication.
But, if you've built your whole company around proprietary lamda functions and a vast range of AWS offerings, you're setting up yourself to never get out of the mess.