In Internet Information Services (IIS), the "Windows Process Activation Service" (WAS) plays a crucial role in managing the IIS configuration and related settings. WAS is a Windows service responsible for the management of application pools, which provide process isolation and resource management for web applications hosted on IIS.
Here's how WAS manages the IIS configuration file:
1. Reading and Monitoring Configuration:
When IIS starts, WAS reads the "applicationHost.config" file, which contains the global and site-specific configurations. This file includes settings related to the web server, sites, application pools, modules, handlers, and other features of IIS. WAS keeps this information in memory and monitors changes to the configuration file.
2. Application Pool Management:
WAS is responsible for starting, stopping, and recycling application pools based on the configuration specified in "applicationHost.config." Each application pool represents a group of web applications that share the same configuration settings and worker processes. When an application pool is created or modified, WAS ensures that the associated worker processes are started or restarted as needed.
3. Dynamic Configuration Changes:
One of the significant advantages of WAS is its ability to apply configuration changes dynamically without requiring a full restart of IIS. When you modify the "applicationHost.config" file or use IIS Manager or other management tools to change settings, WAS can apply these changes without interrupting the operation of other web applications. It can recycle individual application pools to apply new configurations to the updated web applications.
4. Health Monitoring and Recovery:
WAS monitors the health of worker processes and detects when an application pool or worker process becomes unhealthy due to various issues such as crashes or excessive resource usage. If an application pool or worker process fails, WAS can automatically recycle or restart it to restore service without affecting other applications.
5. Managing Worker Processes:
WAS creates and manages the worker processes (w3wp.exe) associated with each application pool. It ensures that the correct number of worker processes is running based on the configuration settings and system resources available.
6. Programmatic Configuration Changes:
You can also use the .NET API called "Microsoft.Web.Administration" to programmatically manage the IIS configuration. This API allows developers to read and modify the IIS configuration settings, and any changes made using this API are managed by WAS.
Overall, WAS plays a vital role in managing the IIS configuration, ensuring the stability and performance of web applications, and handling dynamic configuration changes without requiring full restarts of IIS. It simplifies the management of application pools and allows IIS to efficiently serve web content.