What was the monthly revenue for this startup? Those are absolutely insane numbers.
Problems come from many areas... like the fact it was in the data management space and the 1500 or so i3's running Cassandra plus the hybrid cloud approach of front end in AWS talking to APIs in GKE which talked to backends in AWS because cool technologies you know.
No architecting was done. Build this and put it in the cloud. The team from RU didn't even know about autoscaling groups and when I tried to bring them in I ran into resistance.
I have many examples of "opportunities to optimize" from this place, needles to say my stress level is much lower not being there.