Web Server Basics

Even if you focus primarily on what’s commonly referred to as “front-end” web development—HTML documents and web graphics—the server and the way it is configured may impact the way you work. In most cases, there is no way to avoid making first-hand contact with the server, even if it’s just to upload files.

For this reason, all web designers should have a basic level of familiarity with servers and what they do. At the very least, this will enable you to communicate more clearly with your server administrator. If you have permission for greater access to the server, it could mean taking care of certain tasks yourself without needing to wait for assistance.

Servers 101

A server is any computer running software that enables it to answer requests for documents and other data. The programs that request and display the documents (such as a browser) are called clients. The terms “server-side” and “client-side,” in regard to specific functions like imagemaps, refer to which machine is doing the processing. Client-side functions happen on the user’s machine; server-side functions occur on the remote machine.

Web servers answer requests from browsers (the client program), retrieve the specified file (or execute a CGI script) and return the document or script results. Web browsers and servers communicate via the Hypertext Transfer Protocol (HTTP).

Popular Server Software

As of this writing, the majority of web servers are running on the Unix platform. This is why a lot of Unix terminology is still used in the web world. You may even need to learn a few Unix commands in the course of a job. However, the percentage of Windows NT, Windows 95, and even Macintosh servers is steadily increasing. Some server packages offer a graphical interface as an alternative to Unix command-line controls.

Some popular servers include:

NCSA Server
This is publicly available server software maintained by the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. It runs on the Unix platform.

Apache
A variation of NCSA, Apache has become the most popular web server due to the fact that it is a powerful server and it is available for free. It runs primarily on Unix, but is being released to run on other platforms, including Windows NT.

CERN
This server, maintained by the World Wide Web Consortium, is publicly available from http://www.w3.org. It is also Unix-based. Netscape Servers Netscape provides a variety of commercial server packages that run on Unix and NT platforms.

Internet Information Server (IIS)
This is Microsoft’s server package. It is freely available, easy to install and configure, and runs on Windows NT and 95 platforms.

The majority of servers today (approximately 70%) run Apache or its predecessor, NCSA. The particular brand of server does not impact the majority of things the designer does, such as making graphics or developing basic HTML files. It will certainly influence more advanced web site building techniques such as Server Side Includes, adding MIME types (discussed later in this chapter), and database-driven web pages. Be certain to coordinate with your server administrator if you are using your server in ways beyond simple HTML and graphic files storage.

Basic Server Functions
As a web designer, it is important that you have some level of familiarity with the following elements of the web server.

Root directory

When a browser requests a document, the server locates the document, starting with the document root directory. This is the directory that has been configured to contain all documents intended to be shared via the Web. The root directory does not necessarily appear in the URL that points to the document, so it is important to know what your root directory is when uploading your files.

For example, if the root directory on littlechair.com is /users/httpd/www/ and a browser makes a request for http://www.littlechair.com/super/cool.html, the server actually retrieves /users/httpd/www/super/cool.html. This, of course, is invisible to the user.

Index files

A forward slash (/) at the end of a URL indicates that the URL is pointing to a directory, not a file. By default, servers display the contents of the directory specified in the URL. Most servers are configured, however, to display a specific file, called the index file, instead of the directory list. The index file is generally named index.html, but on some servers it may be named welcome.html or default.html. This is another small variation you will need to confirm with your server administrator.

If the server is configured to look for the index file and does not find one, the directory contents may be displayed instead, leaving your files vulnerable to snooping. For this reason, it is a good idea to always name some page (usually the main page) in each directory “index.html” (or an otherwise specified name).

HTTP response header

Once the server locates the file, it sends the contents of that file back to the browser, along with some HTTP response headers. The headers provide the browser with information about the arriving file, including its media type (also known as “content type” or “MIME type”). Usually, the server will determine the format from the file’s suffix; for example, a file with the suffix .gif is taken to be an image file.

The browser reads the header information and determines how to handle the file, either displaying it in the window or launching the appropriate helper application or plug-in. MIME types are discussed further at the end of this chapter.

CGI scripts

Instead of pointing to an HTML file, a URL may request that a CGI program be run. CGI stands for Common Gateway Interface, and it’s what allows the web server to communicate with other programs (CGI scripts) that are running on the server. CGI scripts are commonly written in the Perl, C, or C++ languages.

CGI scripts can be used to perform a wide variety of functions such as searching, server-side imagemap handling, and gaming; however, their most common usage is forms processing.

Most server administrators follow the convention of keeping CGI scripts in a special directory named cgi-bin (short for CGI-binaries). Keeping them in one directory makes it easier to manage and secure the server. When a CGI script is requested by the browser, the server performs the function and returns the dynamic content to the browser.

Next >> Web Services