> but all that requires application code changes and significantly more configuration management. And not to talk about making them highly available, scalable,

> but all that requires application code changes and significantly more configuration management. And not to talk about making them highly available, scalable, having to continuously monitor and so on takes time, effort and involves significant opportunity costs. Imagine business folks telling engineers about an upcoming promotion campaign that bring in 3X more load. Outside of AWS (or cloud provided service) one has to sit and plan for scaling up all the individual components (rabbitmq, haproxy etc.,) which really becomes pain after a few iterations.