7.5. Apache web server
Apache works best when it is delivering static content. But if you're only delivering static content, you should consider using Tux, the Linux kernel HTTP server.
There are a number of small quick-tips you can use to increase the throughput and responsiveness of Apache.
One such tip is to turn off DNS resolving in Apache. When Apache receives a request to send data to a remote server, Apache will request a reverse DNS lookup on that IP address. While the requests winds its way through the DNS heirarchy, Apache is stuck waiting for the answer before it can send the page back to the requesting client. By turning this feature off, Apache will merely log the IP address without name in its log file, and then deliver the page. A problem with this is if the machine is cracked through the web server, you will have to do your own reverse DNS lookup to find out what country and domain the machine is from. A way to have the best of both worlds is to run a caching-only name server run on the local network or on the web server box itself. This allows Apache to quickly get the DNS information, and store a hostname and domain instead of just an IP address.
Cutting the size of graphic images is also a way to improve performance. Using algorithms such as JPG or PNM will cut the size of the image file without reducing the quality of the image by much. This allows more image files to go out per second.
Instead of reinventing the wheel, see if Apache has a module for the feature you need. Modules for authentication against SMB, NIS, and LDAP servers all exist for Apache, and you will not have to add the functionality to your server side scripts.
Make sure your database is tuned properly. This has been covered in Section 7.3, but a poorly tuned database can slow everything down. If you expect heavy usage, do not put the database and web server on the same machine. One machine running the database, and another running the web server connected by high speed (gigabit Ethernet) will allow both machines to operate quickly.
Since so many web sites are using server-based applications and CGI, it makes sense to take a look at the server interpreters being used. If you use a language like Java that is known to be pretty slow, you can expect lower performance as compared to using applications compiled in C.
But Java has its own advantages over C. The biggest is that Java is designed to be much more portable than C is. Since Java is an object oriented language, its code reuse is much better, allowing delopers to create applications quicky.
There are three other major server languages used by Apache. These are Perl, Python, and PHP. All three are included in most Linux distributions, and if they're not on your system, each is easy to install and get working.
7.5.1. Perl
Perl is pretty much the granddaddy of CGI and server programs. It has excellent string manipulation abilities, plenty of libraries to let you create web applications quickly, and has drivers for just about anything you want to do. It is known as the programmer's swiss army knife, and for good reason.
The downside to perl is that it is an interpreted language, meaning each time a perl application is run, the perl interpreter has to be loaded, the application has to be loaded into memory, and the interpreter has to compile the application. This can create a heavy load on a system.
The best way around this is to use the mod_perl library with apache. This library first loads the perl interpreter so it is always in memory and ready to run. It also caches frequently-used perl CGI scripts in memory already in a precompiled state. When a perl application starts up, many of the bottlenecks (loading and interpreting) have already been done. The cost to the sysadmin and programmer is that mod_perl takes up a lot of memory, and its memory use will increase as more perl scripts are added to a web server.
 | Adding more memory and CPU speed to a machine running mod_perl will improve its performance. |
7.5.2. Python
Python was one of the first of the interpreted languages to implement object oriented programming, allowing programmers to reuse and share code. It also learned a bit from perl and it's interpreted nature by comiling python code into a pre-compiled format. This format is not portable like Java, but does much of the grunt work of compiling a python application. The python interpreter then spends less time compiling the application each time it's run.
Programmers may cringe a bit when they start writing in python. Syntax is much more strict than C or Perl, using tabs and newlines to delineate parts of code. And, like perl, python requires the interpreter to load into memory and run.
There is also a mod_python for apache that operates simiar to mod_perl. More memory and CPU speed will be a great improvement.
7.5.3. PHP
PHP is a relative newcomer to the languages listed here. But PHP was designed for server side applications. The interpreter is a module in apache, and PHP code can exist within a HTML page, allowing authors to combine the web page and application into one file.
PHP has two downsides to it from a programer's perspective. First, PHP is still relatively new. It is not quite as seasoned as Perl or Python, each of which have over ten years worth of development behind them. Second, PHP does not have modules that can be easily loaded and used like Perl and Python have. If your implementation of PHP does not have the graphics libraries installes, you will have to recompile PHP and add them in. Neither of these should prevent you from giving a serious look at using PHP for your server side application.