How to deploy an ASP.NET Application with zero downtime

Question

To deploy a new version of our website we do the following:

1. Zip up the new code, and upload it to the server.
2. On the live server, delete all the live

Answer 1

I would refine George's answer a bit, as follows, for a single server:

1. Use a Web Deployment Project to pre-compile the site into a single DLL
2. Zip up the new site, and upload it to the server
3. Unzip it to a new folder located in a folder with the right permissions for the site, so the unzipped files inherit the permissions correctly (perhaps e:\web, with subfolders v20090901, v20090916, etc)
4. Use IIS Manager to change the name of folder containing the site
5. Keep the old folder around for a while, so you can fallback to it in the event of problems

Step 4 will cause the IIS worker process to recycle.

This is only zero downtime if you're not using InProc sessions; use SQL mode instead if you can (even better, avoid session state entirely).

Of course, it's a little more involved when there are multiple servers and/or database changes....