IIS Technology Intelligence

What is IIS?

Internet Information Services (IIS) is Microsoft's extensible web server software integrated into Windows Server and available on Windows desktop editions. First released with Windows NT 3.51 in 1995, IIS has evolved into a robust enterprise platform serving websites, web applications, and web services in Windows environments.

IIS powers millions of websites globally, particularly in enterprise environments where Windows Server infrastructure is standard. It's tightly integrated with the .NET ecosystem, making it the natural choice for ASP.NET, ASP.NET Core, and legacy ASP applications. Fortune 500 companies widely deploy IIS for internal applications and public-facing websites.

The current version, IIS 10, ships with Windows Server 2016/2019/2022 and Windows 10/11. It supports modern protocols including HTTP/2, WebSockets, and TLS 1.3. The modular architecture allows administrators to install only required features, improving security and reducing attack surface.

IIS Architecture

Application Pools: IIS isolates web applications in separate worker processes (w3wp.exe). Each application pool has its own memory space, identity, and configuration. Pool recycling automatically restarts workers to prevent memory leaks and maintain stability.

HTTP.sys Kernel Driver: Request processing begins at the kernel level with HTTP.sys. This driver handles connection management, caching, bandwidth throttling, and logging before passing requests to user-mode worker processes. Kernel-mode caching dramatically improves static content performance.

Pipeline Architecture: IIS uses an integrated request pipeline where native modules and managed .NET modules process requests. Authentication, URL rewriting, compression, and caching are implemented as modules. Custom modules extend functionality without modifying core server code.

Configuration System: Hierarchical XML configuration in applicationHost.config and distributed web.config files. Configuration inheritance allows global defaults with per-site and per-application overrides. The Configuration Editor provides GUI access to all settings.

Worker Process Isolation: Unlike single-process servers, IIS runs each site/application in dedicated processes. Crashes don't affect other applications. Different applications can run under different identities with least-privilege security.

IIS Use Cases

ASP.NET Applications: The definitive platform for ASP.NET Framework and ASP.NET Core applications. Seamless integration with Visual Studio deployment, Windows Authentication, and .NET runtime management.

Enterprise Intranets: Internal corporate websites with Active Directory integration. Single sign-on via Windows Authentication. SharePoint, Exchange OWA, and custom line-of-business applications.

Hybrid Reverse Proxy: Application Request Routing (ARR) module enables reverse proxy to Node.js, PHP, or Linux backends. Load balancing across server farms. URL rewriting for clean URLs and redirects.

FTP/FTPS Services: Built-in FTP server with SSL support. User isolation, virtual directories, and Active Directory authentication. Common for file transfer in Windows environments.

WebDAV File Sharing: Web-based file access with WebDAV module. Map network drives over HTTP/HTTPS. Document collaboration without VPN.

Legacy Application Hosting: Classic ASP and COM+ application support. ISAPI extensions for legacy software. Migration path for decades-old Windows web applications.

IIS Configuration Examples

Web.config URL Rewrite

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
                <rule name="HTTPS Redirect" stopProcessing="true">
                    <match url="(.*)" />
                    <conditions>
                        <add input="{HTTPS}" pattern="off" />
                    </conditions>
                    <action type="Redirect" url="https://{HTTP_HOST}/{R:1}"
                            redirectType="Permanent" />
                </rule>
                <rule name="SPA Fallback">
                    <match url=".*" />
                    <conditions logicalGrouping="MatchAll">
                        <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
                        <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />
                    </conditions>
                    <action type="Rewrite" url="/index.html" />
                </rule>
            </rules>
        </rewrite>
        <staticContent>
            <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" />
        </staticContent>
    </system.webServer>
</configuration>

IIS Benefits

Windows Integration: Native Active Directory authentication. Group Policy management. Windows Event Log integration. PowerShell administration via WebAdministration module.

.NET Excellence: Best-in-class ASP.NET support. In-process hosting for ASP.NET Core delivers exceptional performance. Seamless deployment from Visual Studio.

Enterprise Management: Centralized configuration with Shared Configuration. Web Farm Framework for multi-server deployments. IIS Manager remote administration.

Security Features: Request filtering blocks malicious requests. Dynamic IP restrictions. Built-in SSL certificate management. Windows Firewall integration.

GUI Administration: Graphical IIS Manager simplifies configuration. No command-line required for common tasks. Configuration Editor exposes all settings visually.

Robust Isolation: Application pool isolation prevents cross-application interference. Automatic recycling maintains stability. Failed Request Tracing aids debugging.

Licensing: Included with Windows Server licenses. No additional cost for enterprise deployments. Consistent with existing Microsoft licensing agreements.