Internet Information Services (IIS) 8.5 is an extensible web server created by Microsoft for use with Windows NT family. IIS 8.5 is included in Windows Server 2012 R2 and Windows 8.1. This version includes Idle worker-Process page-out, Dynamic Site Activation, Enhanced Logging, ETW logging, and Automatic Certificate Rebind.

IIS 8.5 has several improvements related to performance in large-scale scenarios, such as those used by commercial hosting providers and Microsoft's own cloud offerings. It also has several added features related to logging and troubleshooting. The new features are:

• Idle worker-Process page-out – a function to suspend idle site to reduce the memory footprint of idle sites. In IIS 8.5, the Administrator has the option of suspending an idle worker process rather than terminating it. A suspended worker process remains alive but is paged-out to disk, reducing the system resources it consumes. When a user accesses the site again, the worker process wakes up from suspension and is quickly available.
• Dynamic Site Activation – a feature that registers listening queues only to sites that have received requests.
• Enhanced Logging – Now you can customize the logging to store request headers, response headers and server variables. The customization can be used to get information such as the IP addresses of connecting clients when the network has a load balance.
• ETW logging – Event Tracing for Windows (ETW) provides application programmers the ability to start and stop event tracing sessions, instrument an application to provide trace events, and consume trace events. Trace events contain an event header and provider-defined data that describes the current state of an application or operation. You can use the events to debug an application and perform capacity and performance analysis.
• Automatic Certificate Rebind – a feature that detects when a site certificate has been renewed, and automatically rebinds the site to it