Web Farm / Load Balanced environment installation

First of all, to install the software in a load balanced (web farm or web cluster ) environment, you will need a license for each web server you have the ASP.NET files installed.

The problem with using the forum software in a load balanced environment is that since our software keeps attachment locally on the file system instead of on the database for performance reasons, each server will have its copy of attachments and you need to do something to synchronize its content (the content in the ~/upfiles directory).
 
The following is an approach that in instead of synchronizing the files among servers, you instruct all servers to upload / download attachments to / from a single server.

Let's say you have 2 web servers, W-A (the current web server) and W-B (a new one you just added).

1. First, create a mirror account on your server W-A and W-B (not Network Service) and give this mirrored account modify permission on the ~/upfiles folder on W-A. A mirrored account is an account that exists on both servers that has the same username and password.
2. Then, on W-B, delete the ~/upfiles local folder and use the IIS management console on W-B to create a virtual directory under the forum root folder and name it "upfiles", which points to the ~/upfiles folder on W-A. In the virtual directory creation wizard, specify to use the mirrored account to connect to the ~/upfiles folder on W-A, and give "write" access permission.
3. IIS 6 users: Make sure you impersonate the mirrored account instead of using the default NETWORK SERVICE account. Add the following to the web.config file on W-B
   
   <identity impersonate="true" userName="mirrored account name" password="mirrored account pass" />
   
   to the <system.web> section.
4. IIS7 or above: you will use the above impersonation trick, or you can configure the Application Pool the forum software uses to run under the mirrored account for W-B.

That's it. You will now upload/download all files directly to / from W-A's ~/upfiles directory.

Hey Samuel, I just upgraded to the newer version of the software and will begin testing load balancing. In the example above you mention 3 servers to file uploads, I plan to set up only two. (primarily for redundancy)

Our environment currently uses NLB w/Affinity and DFS (the newer version) between the servers. After reading around, it would seem that if both servers use the same DFS path for the upfiles then uploading should work without problem - correct?

I don't see any reason why it wouldn't but just want to make sure before I start going down that road.  [security will all be configured correctly, not worried about that]

There are 2 issues with load balanced environment

1. software license - you will need to make sure each server you have forum files on has a license. In your case, you will need an additional software license.
2. DFS - I am not sure what the new version suggests, but as long as the ASP.NET account can map the shared folder correctly (Server.MapPath can get to the folder), it should work. It is probably best to use our approach described here.

Perfect. 

1) I will be acquiring an additional license soon then.

2) That's exactly what I was assuming.

[By "newer" I meant DFS with DFSR instead of DFS with FRS (the newer replication service)]

I'll let you know if I have any issues.