Web Servers

What is a Web Server?

• Server software that handles and understands HTTP/HTTPS request/response
  • Listen default on port 80 (HTTP) or port 443 (HTTPS)
• Serve static web resources
  • Reading from file system
  • HTML pages, Documents, static files (CSS, JS, IMG), streaming media
• Serve dynamic web resources
  • Support server-script laguages/platforms (like PHP, ASP.NET...)
  • Render web data on-the-fly (HTML, JSON...)
  • Communicate with databases
  • Send request to other servers

Web Servers

• Apache
  • The A in LAMP-stack (Linux, Apache, MySQL, PHP)
• Nginx
  • Uses an asynchronous event-driven approach to handling requests
• IIS for Windows server (Internet Information Services)
  • .NET
• Apache Tomcat
  • A Java servlet, HTTP Connector, JSP engine
  • A Java servlet is a Java program that extends the capabilities of a server.
• Node.js
  • A platform! Create a web server through code (APIs)!

About Apache

• The most used web server on the Internet
  • http://w3techs.com/technologies/overview/web_server/all
• Open-source HTTP server for both UNIX and Windows
  • Apache Software Foundation
• The Apache HTTP Server was launched in 1995
  • Based on NCSA HTTPd server
  • Name: "Native American Indian tribe of Apache" / "A-patchy-server"
• Every request is spawn to a own thread (like a own process)
  • Thread pool
• Loadable Dynamic Modules which extend the core functionality.
  • mod_access, mod_auth, mod_rewrite
• .htaccess

About Nginx ("engine x")

• Free web server, 2004, second most used (?)
  • http://w3techs.com/technologies/overview/web_server/all
  • Also used as other type of servers like (reversed) proxy, load balancer, cache server
• Nginx uses an asynchronous event-driven approach to handling requests
  • Non-blocking mode in a single main thread
  • Event-loop receiving event from a queue (like javascript event-loop)
• The company Nginx provide and support Nginx Plus as paid software
• nginx.conf

About IIS (Internet Information Services)

• Microsoft, tight coupled to Windows
• Using modules and extensions
• Graphic Administration (tight connection to the operating system)
  • or Powershell
• .NET applications

Running a web server on Node.js

const http = require('http');
const PORT = 8080;

http.createServer((req, res) => {
  res.writeHead(200);
  res.end('Hello world\n');
}).listen(PORT);

Different kind of servers in a web environment

• Reverse proxy
• Load balancer
• Cache server
• Application server
• Virtual hosting

Reverse proxy

• Hide the origin server or servers
• act as firewall can protect against common web-based attacks, such as DOS or DDOS
• Distribute the load from incoming requests to several servers
• Handle HTTPS

Load balancer

• Scaling, handle more traffic
• Load balance traffic over more replicas
  • Horizontal scaling (more machines)
  • Vertical scaling (more hardware)

Application server

• Most of the times equals to web server
• A Web server always handle HTTP
• Application server could also handle other requests

Virtual hosting

• A web server is hosting one or more domain names on a single server
  • example.com could share resources with example.se
• Multiple web sites on one server

Not just web servers...

• HTML - SGML, "documentation language" with ideas from 60s (the a-tag)
• URI/URL - "hypertext name", Address resources
• HTTP - Hypertext transfer protocol

How...?

What happens when you enter an URL in your browser and press enter?

How does the web server get and understand the request?

Need to find where to send the HTTP request...

• Humans like domain names
  • lnu.se, sunet.se...
• Computers like numbers like IP-addresses
  • 194.47.110.87, 2001:6b0:52:4000::5:5
• To take care of the translation and organization of this we have DNS
  • Domain name server
  • Servers around the world connected in a hierarchic structure

A DNS query

What is the IP-address of lnu.se?

We have the address to the server - Use the Internet

• The browser (and the underlaying OS) creates "a TCP/IP packet"
  • TCP, IP, HTTP
  • How to connect, the address, the information to the server

We have the address to the server - Use the Internet

• The browser sends this to its default router
  • The router is connected to internet and a lot of other routers
  • They analyzes the IP address and know how to send it further
  • The routers on the internet make sure it will go to the right server

Routing

The server gets the packet

• Analyze the TCP (and IP) information
  • What port should we connect to?
  • to which address and on what port should I send back the response?
• Hopefully the web server listens to the right port
  • The web server analyze the HTTP information and do the magic...
  • Create new packet and send it back to the client (along with the data)