Is there a way to deploy new code with Tornado/Python without restarting the server?

I've recently started to experiment with Python and Tornado web server/framework for web development. Previously, I have used PHP with my own framework on a LAMP stack. With PHP, deploying updated code/new code is as easy as uploading it to the server because of the way mod_php and Apache interact.

When I add new code or update code in Python/Tornado, do I need to restart the Tornado server? I could see this being problematic if you have a number of active users.

(a) Do I have to restart the server, or is there another/better way?

(b) If so, how can I avoid users being disconnected/getting errors/etc. while it's restarting (which could take a few seconds)?

[One possible thought is to use the page flipping paradigm with Nginx pointing to a server, launch the new server instance with updated code, redirect Nginx there and take down the original server...?]

Solution

It appears the best method is to use Nginx with multiple Tornado instances as I alluded to in my original question and as Cole mentions. Nginx can reload its configuration file on the fly . So the process looks like this:

Update Python/Tornado web application code
Start a new instance of the application on a different port
Update the configuration file of Nginx to point to the new instance (testing the syntax of the configuration file first)
Reload the Nginx configuration file with a kill -HUP command
Stop the old instance of Python/Tornado web server

A couple useful resources on Nginx regarding hot-swapping the configuration file:

https://calomel.org/nginx.html (in "Explaining the directives in nginx.conf" section) http://wiki.nginx.org/CommandLine (in "Loading a New Configuration Using Signals" section)