A worker is usually something that does background processing. For example a user uploads an image and you need to convert it to multiple sizes. You can either do this on your application server within the scope of the request, or set up a task queue.

Here's an oversimplification of the latter: You have an application server, a queue (something like 0MQ, or redis) and one or multiple workers. When the image is posted, you add a job to the queue, asking for the image to be processed. The worker polls the queue asking if there are any jobs, an if there are, it executes those.

> I never package my web app. It just runs and runs and runs. And my customers use it.

So how do you deploy a new version of your app?