Load Balancer Stops Sending Traffic to SharePoint Due to IIS SPRequestFilterModule
Symptoms The load balancer (F5) is no longer sending web traffic to one of its pool members (SharePoint frontend) because it detects that the server is down. Diagnosis IIS logs show the load balancer probes as follows: Note that the HTTP status code ( sc-* ) is 0.0.2 . The Win32 status of 2 , which commonly corresponds to ERROR_FILE_NOT_FOUND when a default page (such as default.aspx or index.html) is missing, is misleading for SharePoint. SharePoint does not even store a default page in the site's root directory, and the load balancer is not configured to look for any default files. What's more relevant here is that the server returned 0 bytes to the client and logged a 0 ms response time , indicating the request failed immediately in IIS before it reached the SharePoint/application layer. Therefore, the failure likely occurred earlier in the request pipeline during the native module handoff. While multiple factors could cause behavior like this (for exa...