Service Unavailable - Error seen for all the SharePoint Websites

Service Unavailable is very generic error message seen in the world of SharePoint and IIS. The other day I was working on a case where in we were getting "Service Unavailable". It should have been simple and quickly resolvable, however, the issue was very much typical and spanned towards the IIS fucntionality.

 

Once, I ensured that the issue is not due to an application pool or resyncing of passwords etc., I created a new IIS site and observed that even the default IIS site was exhibiting the same behavior. Later we realized that the issue is a known issue because of an update, as per the KB article: https://support.microsoft.com/kb/973917

 

Prior to applying the resolution ensured that the update (973917) is seen in the installed updates of the Add/remove program. Then, applied Windows 2003 SP2, in this scenario.

 

Details are given below:

Internet Information Services 6.0 may not function correctly after installing KB973917 https://support.microsoft.com/?kbid=2009746