Couldn’t this be solved at the load balancer level by only allowing each running instance of the monolith to serve its own subset of the routes? It can even be

Couldn’t this be solved at the load balancer level by only allowing each running instance of the monolith to serve its own subset of the routes? It can even be done dynamically on the fly. If the instances begin to struggle, divide them in half and see which half has the problem. Then divide that one in half, and so on, until you have isolated the problem. Then stop those requests altogether and have capacity over for all the people desperately hitting F5. So now you have both DOS resilience and independent scaling, all without requiring any changes to the architecture or knowing in advance exactly what you should have factored out into its own service.