Top IIS (Internet Information Services) Interview Questions and Answers

What is IIS (Internet Information Services)?

IIS (Internet Information Services) is a popular web server developed by Microsoft for hosting websites and web applications. It runs on Windows and is used to handle HTTP requests, serve web pages, and manage web applications. IIS handles requests from clients, processes them, and sends back responses. It plays a vital role in deploying and managing web applications and provides functionalities for various protocols (HTTP, HTTPS, FTP, etc.).

Key Features of IIS

• Supports web applications and web services.
• Handles requests from clients and manages responses.
• Provides security features (access controls).
• Supports various protocols (HTTP, HTTPS, FTP, SMTP, etc.).
• Improved performance, reliability, and scalability compared to previous versions.
• Simplified application deployment and management.

Hosting a Website on IIS

Two common ways to host a website on IIS are:

• Using folder web sharing (a simple approach for serving static content).
• Creating a virtual directory (maps a website's files to a specific location on the server, enabling organization and improved management of multiple websites).

Key Functionalities of IIS

IIS manages the processing of requests and responses for web applications. When a client requests a resource, IIS receives the request, passes it to the appropriate application pool (which contains worker processes for handling requests), processes the response, and then sends it back to the client.

Protocols Supported by IIS

IIS supports a range of network protocols, including:

• HTTP (Hypertext Transfer Protocol)
• HTTPS (HTTP Secure)
• FTP (File Transfer Protocol)
• FTPS (FTP Secure)
• SMTP (Simple Mail Transfer Protocol)
• NNTP (Network News Transfer Protocol)

Kernel Mode vs. User Mode in IIS

IIS operates in both kernel mode (closer to the operating system, handling low-level tasks) and user mode (handles application-level tasks). This layered architecture enhances performance and security.

New Features in IIS 8.5

• Enhanced logging capabilities for improved security monitoring and troubleshooting.
• Dynamic site activation (improves performance by only activating websites when needed).

Virtual Directories in IIS

A virtual directory in IIS maps a website to a physical directory on the server. This is important for organizing websites and managing multiple sites on a single server.

IIS Versions and Operating Systems

Application Pools in IIS

Application pools in IIS isolate web applications from each other, improving security and manageability. Each application pool runs in its own worker process, preventing problems in one application from affecting others.

SVCHost.exe Components

SVCHost.exe is a process hosting various Windows services, including:

• W3SVC (World Wide Web Publishing Service): The core IIS service.
• WAP (Windows Activation Process): Manages software licensing and activation.

IIS Web Farms

An IIS web farm distributes web traffic across multiple servers using a load balancer. It provides high availability, scalability, and performance.

Advantages of IIS Web Farms

• High availability.
• Improved performance.
• Scalability.
• Simplified maintenance.

Setting up an IIS Web Farm

1. Install IIS on all servers.
2. Configure the servers for your web application.
3. Configure load balancing (using a load balancer).
4. Configure SSL certificates.
5. Deploy your web application.

Web Gardens in IIS

A web garden runs multiple worker processes for a single application pool on a single server, improving scalability and availability within that server.

Advantages of Web Gardens

• Improved performance (for non-CPU-bound apps).
• Increased capacity for handling requests.
• Enhanced application availability.

Web Farm vs. Web Garden

DefaultAppPool in IIS

DefaultAppPool is the default application pool created when IIS is installed. It should not be deleted unless you understand the implications; deleting it could impact your IIS functionality.

Application Pools in IIS

Application pools provide isolation and management for web applications in IIS, preventing issues in one application from affecting others.

IIS Log Files

IIS log files record details about web server activity, including requests, responses, errors, and other relevant statistics. These logs are essential for monitoring website performance, troubleshooting issues, and identifying potential security threats. Log files typically include information such as timestamps, IP addresses, request methods, status codes, and data transfer volumes.

Enhanced Security Features in IIS 7.5

IIS 7.5 introduced several security improvements:

• IP address and location restrictions
• URL authorization
• Client certificate mapping
• Request filtering

Default Application Pool Identity

The default identity for an application pool in IIS is "Network Service". This account has limited privileges, improving security.

IIS 7.0 Modular Architecture

IIS 7.0 introduced a modular architecture, improving flexibility and manageability. Key modules include:

• Content Module: Serves static content.
• Compression Module: Compresses content to improve performance.
• Caching Module: Caches content to improve response times.
• Security Module: Handles authentication and authorization.
• Logging and Diagnostic Module: Records logs for monitoring and troubleshooting.

Application Pool Identities

Application pool identities in IIS provide a mechanism to run application pools under specific user accounts without needing to create and manage individual domain or local accounts. This improves security by limiting the privileges of the application pool.

ISAPI (Internet Server Application Programming Interface)

ISAPI is a Microsoft technology for extending IIS functionality. It's more efficient than CGI (Common Gateway Interface) and is used by ASP.NET applications. ISAPI allows creating extensions (handle requests) and filters (modify requests and responses).

Enabling ISAPI in IIS

1. Open the Server Manager.
2. Select "Add Roles and Features".
3. Choose "Role-based or feature-based installation".
4. Select your server.
5. Select "Web Server (IIS)" and then add the ISAPI Extensions feature.
6. Complete the installation.

Default Anonymous User Name

The default anonymous user name is "IUSR_MachineName", where "MachineName" is the name of the server.

Application Pool Recycling

Application pool recycling in IIS periodically restarts application pools. This helps free up memory and maintain system stability.

Remote Debugging of IIS

Remote debugging of IIS is required when:

• IIS isn't installed on the development machine.
• The development and deployment environments differ.
• Multiple developers need simultaneous debugging access.

The msvsmon.exe (Remote Debugger) is used for this purpose.

IIS Security Settings

IIS provides various security settings including:

• Authentication methods (basic, digest, Windows authentication, etc.).
• Authorization rules.
• IP address restrictions.

ISAPI Filters

ISAPI filters intercept and modify HTTP requests and responses. They provide a mechanism for extending IIS functionality (e.g., authentication, compression, logging).

Enabling Pinging in Application Pools

Enabling pinging allows IIS to monitor the health of worker processes. It helps detect and address issues such as hung or unresponsive processes.

Protocol Listeners in IIS

Protocol listeners in IIS are used for receiving requests (from clients), passing requests to the worker processes and returning responses.

HTTP.SYS in IIS

HTTP.SYS is a kernel-mode HTTP listener that receives HTTP requests before handing them off to IIS for processing. It's a critical component of IIS, operating in kernel mode.

SVCHost.exe Components

SVCHost.exe hosts multiple Windows services, including:

• World Wide Web Publishing Service (W3SVC): Core IIS service.
• Windows Activation Process (WAP): Manages software licensing.

IIS Metabase

The IIS metabase is a hierarchical database storing IIS configuration settings.

User Mode Subsections in IIS

User mode in IIS includes the Web Admin Service, virtual directories, and application pools.