Strategies for pushing updates to an ASP.NET webfarm?

Question

How do most people handle updating ASP.NET applications running in a webfarm? I am having the problem that because the app is in use and the request affitnity is not sticky, when we push the update users run into errors as the process requests the request might be handled by the wrong version of the application. How do you do this? Take the entire application offline and let the push complete or do you update live and let the chips fall where they may? Ideally we'd like to minimize down time if at all possible.

any thoughts/suggestions/pointers would be appreciated

Answer 1

Make half the servers inaccessible, update those, flip all the inaccessible servers to accesible and vice versa, update the other half, and put the other half back up.

Answer 2

This is what we do:

Drain the active sessions off a particular server in the farm no new traffic will be routed to that server during the time.

Apply the patch to the drained server

Drain the sessons off the remaining servers

Allow traffic back to the original server

As the other servers are drained, apply the patch and let them come back to life.