AOP type architectures work fairly naturally with out of band queues etc. (0MQ, RabbitMQ or Redis pub/sub off top of my head) so its never really difficult to parallelize those requests out to workers who can largely operate independently. HTTP isn't a silver bullet and for the most part its how public API's are defined - however within your own infrastructure there's a bunch of other transport options, protobuffers, thrift, msgpack or whatever. But yes building some kind of hypervisor or FSM to manage error conditions across a cluster and particularly across datacenters can get out of hand very quickly