Internet Information Services (IIS)

Internet Information Services (IIS) is a web server software created by Microsoft for hosting websites, web apps, APIs, and services on Windows machines. It runs on Windows and integrates tightly with the .NET ecosystem.

In simple terms: IIS is what listens for HTTP/HTTPS requests (from browsers or clients) and returns web pages or API responses.

When to use IIS?

Use IIS when:

• You are hosting ASP.NET / .NET applications
• You’re working in a Windows-based infrastructure
• You need tight integration with Active Directory (Windows authentication)
• You want a GUI-based server management experience
• You’re deploying enterprise/internal applications on Windows Server

Why use IIS?

• Native support for .NET and ASP.NET
• Deep integration with Windows security (users, groups, permissions)
• Easy deployment using familiar Microsoft tools
• Strong support for enterprise environments
• Built-in features like logging, security, and request filtering

Key features of IIS

• HTTP/HTTPS support (including HTTP/2, TLS)
• Application pools (isolate apps for stability)
• Windows Authentication & Active Directory integration
• Request filtering & URL rewriting
• Logging and diagnostics
• SSL/TLS management
• Compression (static and dynamic)
• FTP server support
• WebSockets support
• Scalability via load balancing (with additional tools)

Key components of IIS

1. Web Server Core

Handles incoming HTTP requests and responses

2. Application Pools

Isolate applications into separate worker processes
Prevent one app from crashing others

3. Worker Process (w3wp.exe)

Executes the web application code

4. Modules

Plug-in components that process requests (e.g., authentication, caching)

5. Handlers

Map requests to specific processing logic (e.g., ASP.NET handler)

6. Configuration System

Uses web.config and applicationHost.config

7. Management Tools

IIS Manager (GUI)
PowerShell support

Advantages

1. Tight Windows integration: Works seamlessly with Windows Server, Active Directory, and NTFS permissions
2. Easy to manage: GUI (IIS Manager) is beginner-friendly compared to many alternatives
3. Strong .NET support: Best-in-class hosting for ASP.NET apps
4. Stability via application pools: Fault isolation between applications
5. Built-in security features: Authentication methods, request filtering, IP restrictions
6. Enterprise-ready: Widely used in corporate environments

Disadvantages

1. Windows-only: Cannot run natively on Linux (unlike alternatives)
2. Licensing cost: Requires Windows Server (can be costly at scale)
3. Less popular in modern cloud-native stacks: Many teams prefer Linux + containers + other web servers
4. Performance considerations: Can be heavier compared to lightweight servers in some scenarios
5. Configuration complexity at scale: Advanced setups (load balancing, reverse proxy) can become complex

When IIS is a good choice

• Internal enterprise apps
• Corporate environments using Windows infrastructure
• ASP.NET / .NET Framework applications
• Systems requiring Windows Authentication

When to consider alternatives

• Cross-platform deployments (Linux-heavy environments)
• Containerized microservices
• High-performance edge services

Common alternatives:

• Nginx
• Apache HTTP Server
• Kestrel (often used behind a reverse proxy)