Web Servers

Defining a Web Server

  • A web server is a server that runs software
  • Specifically, this software handles client requests
  • It serves clients with files stored on its server

  • Typically, these files are:

    • HTML files
    • CSS files
    • Some JavaScript files
  • In other words, it usually serves static files to the client
  • These static files include images, videos, forms, etc.
  • Communication between the web server and its client must take the form of HTTP messages

Describing the Functions of a Web Server

  • A web server can be used for the following functions:

    • An HTTP cache
    • A mail proxy
    • A reverse proxy
    • A load balancer
  • A reverse proxy is a server sending resources to a client

  • It fulfills the following functions:

    • Accepts a request from a client
    • Forwards that request to a server that can fulfill it
    • Returns the server's response to the client

  • A load balancer is a server that distributes network traffic across multiple servers

    • A load balancer is a reverse proxy
  • There is a lot of overlap between these functions
  • Therefore, web servers attempt to provide these functions in a centralized service
  • Nginx is a popular web service that achieves this goal

Defining an Application Server

  • An application server is a server that runs software
  • Specifically, this software serves files generated on the fly

  • Some examples of this software are:

    • Gunicorn (Python)
    • Unicorn (Ruby)
  • Web servers achieve the functionality of application servers
  • However, they can remove load from the web server

Motivating Web Proxies

  • Generally, a proxy refers to something acting on behalf of something else
  • Technically, a proxy refers to a server acting on behalf of another server

  • There are two forms of web proxies:

    • Forward proxy
    • Reverse proxy

Defining a Forward Proxy

  • A forward proxy is performed client-side
  • It refers to an intermediary server on the client-side
  • This intermediary server forwards client requests to a server
  • Specifically, it forwards these requests to some web server

  • A forward proxy is used by a client for the following reasons:

    • Client wants to send many requests to a server
    • Client wants to bypass a firewall
    • Client wants to get access to a blocked site

  • The following example involves the use of a forward proxy:

    • There is a client from www.client.com
    • The client is blocked from www.server.com
    • The client uses a proxy server www.proxy.com
    • The proxy server forwards client requests to the server

Defining a Reverse Proxy

  • A reverse proxy is performed server-side
  • It refers to an intermediary server on the server-side
  • This intermediary server forwards client requests to a server
  • Specifically, it forwards these requests to another web server

  • A reverse proxy is used by a server for the following reasons:

    • Server wants to perform load balancing
    • Server wants to prevent DOS attacks
    • Server wants to add a level of security between the client and applciation server

  • The following example involves the use of a reverse proxy:

    • There is a client from www.client.com
    • The client sends a request to the www.server.com
    • The server forwards the request to another server internally
    • This server forwards the request to the application

References

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