HTTP is great because it lets you use the same API in the browser. Given the right services, you can build your front end UI entirely based on your service APIs

HTTP is great because it lets you use the same API in the browser. Given the right services, you can build your front end UI entirely based on your service APIs, no other back end needed. If services used ZeroMQ or Thrift or similar, a browser front end would require an adapter layer. If you have 10+ services, that's a lot of redundant code. Plus: You're leveraging a lot of great infrastructure. With HTTP APIs you can just curl into your APIs. Or load balance and proxy them with HAProxy, Nginx, Varnish etc.