What Is a Web Server?

Every time you load a webpage, something has to answer. Your browser sends a request across the Internet—a question, really—and somewhere, a piece of software receives that question, figures out what you're asking for, and sends back the answer. That software is a web server.

Every website you've ever visited—every search, every purchase, every video—passed through software doing exactly this job: waiting for you to ask, then answering.

While "web server" sometimes refers to the physical machine, in technical contexts it means the software itself: the program listening for HTTP requests and sending HTTP responses.

The Request-Response Cycle

At its core, a web server does six things in an endless loop:

Listen. The server monitors network ports—typically port 80 for HTTP, port 443 for HTTPS—waiting for someone to connect.

Accept. When a browser initiates a connection, the server accepts it, establishing a two-way channel.

Parse. The server reads the HTTP request: What URL are you asking for? What method (GET, POST)? What headers did you send?

Process. Here's where work happens. For a static file, the server locates it on disk. For a dynamic request, it might run code, query databases, or call other services.

Respond. The server sends back an HTTP response—status code, headers, and the actual content (HTML, JSON, images, whatever you asked for).

Log. The server records what happened, creating the access logs and error logs that let administrators see what's going on.

That's it. This simple cycle, repeated billions of times per day across millions of servers, is the mechanism behind the web.

Static vs. Dynamic Content

Web servers handle two fundamentally different jobs.

Static content is file serving. You request an image, CSS file, or HTML document; the server reads the file from disk and sends it to you unchanged. Same file, same content, every time. This is fast—the server is essentially a sophisticated file transfer program. Static content can be cached aggressively, compressed once and reused, and distributed across CDNs worldwide.

Dynamic content is generated fresh for each request. When you check your email or view your social media feed, the server isn't retrieving a file—it's building a response specifically for you, right now, based on your data and the current state of the application.

For dynamic content, web servers interface with application code. The web server receives your request, hands it to an application (written in PHP, Python, JavaScript, or whatever), waits for the application to generate HTML, then sends that generated response back to you.

Popular Web Servers

Apache HTTP Server powered the early web. Released in 1995, it's still widely used today. Apache's architecture assigns each connection to a separate process or thread—straightforward but resource-intensive under high load. Its strength is flexibility: modules let you add almost any feature, and decades of documentation cover almost any scenario.

Nginx ("engine-x") was built in 2004 specifically because Apache struggled with many simultaneous connections. Nginx uses an event-driven architecture where a handful of worker processes can serve thousands of connections simultaneously. It's like a restaurant where three waiters efficiently serve ten thousand tables by never standing still. Nginx dominates high-traffic deployments and is often placed in front of application servers to handle static files, SSL, and load balancing.

Microsoft IIS is the web server for Windows, tightly integrated with the Windows ecosystem. If you're running .NET applications, IIS is the natural choice.

Caddy is a modern web server that automatically obtains and renews SSL certificates with zero configuration. Its simplicity makes it popular for quick deployments.

Essential Configuration

Virtual hosts let one server host multiple websites. The server reads the Host header in each request to determine which site you want—this is how shared hosting works and how you can run multiple domains from one machine.

SSL/TLS enables HTTPS. The server needs certificates, proper cipher configuration, and modern protocol versions. Getting this wrong exposes your users.

Access control determines who can reach what. IP restrictions, password protection, authentication integrations.

Logging records every request and every error. Without logs, you're flying blind.

Performance tuning—timeouts, keep-alive settings, buffer sizes, compression—determines how many users your server can handle and how fast it responds.

Security

Web servers face the Internet directly. They accept input from anyone. This makes security non-negotiable.

Keep software updated. Vulnerabilities are discovered regularly. Running outdated software means running software with known exploits.

Restrict file access. The web server should only read files it needs to serve. Misconfiguration has exposed countless sensitive files to the public Internet.

Use modern SSL/TLS. Outdated configurations let attackers intercept traffic even when you think you're using HTTPS.

Rate limit requests. Prevent abuse by limiting how many requests any single client can make. This protects against denial-of-service attacks and brute force attempts.

Hide version information. Don't tell attackers exactly which software version you're running.

Web Servers vs. Application Servers

These terms cause confusion because modern systems often combine both roles.

A web server handles HTTP. It's excellent at network connections, serving files, SSL termination, and understanding the HTTP protocol.

An application server runs your code. It connects to databases, processes business logic, and generates dynamic responses.

Many deployments use both: Nginx handles incoming requests, serves static files, and forwards dynamic requests to an application server (Node.js, Django, Rails) running behind it. Each component does what it does best.

But the line blurs. Node.js with Express acts as both in a single process. The distinction is more conceptual than architectural—it's about what role the software is playing, not necessarily separate programs.

Performance

Connection handling varies dramatically. Process-per-connection (Apache's traditional model) creates overhead that limits scalability. Event-driven (Nginx) handles many connections with minimal resources.

Static file optimization means compression (gzip, Brotli), cache headers that let browsers store files locally, and serving from memory rather than hitting disk for every request.

Keep-alive connections let multiple requests share one TCP connection, eliminating repeated handshake overhead. Balance keep-alive timeouts: too long wastes resources, too short loses the benefit.

Load balancing distributes requests across multiple web server instances. This scales capacity and provides redundancy—if one server fails, others keep serving.