When installing MOSS 2007 into an existing SPS 2003 environment, you undoubtedly have already decided on a migration strategy i.e. In Place, Database or Gradual.
One of the little gotchas to be aware of if you decided to choose the Gradual migration strategy affects pre-existing web applications. If you look at this screen shot:
You will notice the default state of our web server BEFORE in installation and configuration of the Gradual migration. In our case, we have a web application installed on the web server that is leveraged by the portal. As expected, the web application is installed in a virtual directory under the Default Web Site, in this case called SPSWebApp. Furthermore, it shares the web traffic port i.e. port 80, with the Default Web Site, as it should in order for the WEB application to work properly.
After installing MOSS, successfully running through the Config Wizard and commencing a gradual migration, we see the following in the IIS Manager:
As you know, SharePoint will create a web site called “Default Web Site_Pair” for the new MOSS portal. That web site will be assigned port 80. The old “Default Web Site” web site will have a new TCP port assigned to it, the port you specified in the Gradual Upgrade configuration steps. In our case we used port 8000 and as you can see above, port 8000 is where it now sits.
The problem with this is that any and all web applications such as our SPSWebApp that are installed into virtual directories under the Default Web Site also now have a new port under which they run. Since most web application references and code simply reference the URL without any port specification, IIS would default to port 80 on said web application requests. Given that the web application does not exist on port 80 anymore, such requests would fail with 404 errors.
So, be aware of this little gotcha. The way to work through this is to uninstall your web applications before you commence the gradual upgrade, but after the Config Wizard was done. Then once the new port 80 web site was created, reinstall your web applications to the Default Web Site_Pair web site on port 80.
That should about do it.