While creating web apps, it is vital to keep the time taken to process a request below or around 50 ms. On web applications or web services that have a medium to high rate of requests per second, response time becomes even more paramount. Think of requests such as a flow of liquid that needs to be handled at least as quickly as its flow rate, or else it will overflow. Any extra processing on the server that can be avoided, should be avoided. However, it is quite common to have requirements to operations in a web app that take longer than a couple of seconds, especially when complex database operations or image processing are involved.
In building an application that is able to scale horizontally, it should be possible to decouple all the heavy processing procedures from the web server's layer, and couple them to a worker's layer...
