The queue model in App Engine is little bit different and it's best to take a look at the model before we go into exploring things further. The discussion in this section mainly pertains to push queues, some of which is applicable to pull queues as well but we'll note the differences when we come to pull queues. Basically, you have a queue where you can enqueue as many messages (called tasks from now onwards). This queue then fills up a fixed size bucket (configurable) at a fixed (that too, configurable) rate.

A task is just a URL (which is handled by and is within your application) optionally with query parameters, payload, and headers. Whenever something needs to be done in the background, you simply put it in the queue as a task. Google App Engine will then dispatch HTTP POST call to the URL mentioned in the task along with mentioned query parameters, headers and payload if any. This model of processing is called web hook, which is pretty standard now.

Let's elaborate all this...