First published: 7th March 1997
Feature: Dynamic Page
When choosing how to generate dynamic pages there are serveral
things to consider:
Performance: dynamic pages require more work on the
server, so are less efficient than static files, but some
types of dynamic pages are more resource efficient than
Complexity: dynamic features can be generated from
relatively simple code build into HTML pages (called
"embedded"), through to self contained programs written in
C or perl, using the CGI interface.
Security: some methods of generating dynamic pages
allow you to use a programming or scripting language on
your server. There is a risk of letting users access things
on your system that they should not do if the pages are
Traditionally there were three ways of getting dynamic pages
on your site: use "server side includes" (SSI) inside HTML
pages, use a scripting language such as Perl or PHP, or use a
compiled programming language such as C or Pascal. Both
scripts and compiled programs were accessed using "CGI". But
the distinctions are becoming more blurred. SSI as
implemented in Apache 1.2 now has variables and conditional
execution, making it more like a scripting language, while
the PHP scripting language can be embedded into HTML pages.
There is even a module to embed perl commands into HTML
Also, many scripting languages can be built into Apache as
Apache modules, rather than using CGI. This makes executing
the scripts much more efficient, since an interpreter does
not need to be started for very request.
There are two ways to get the server to run your programs:
either embed a script into an HTML document, or create a
standalone program which makes use of the CGI interface.
Embedded scripts are easier to write but restrict you to the
languages available for embedding, while CGI can be used with
The traditional embedded language is "Server-Side Includes"
(SSI) but other scripting languages are available which can
be embeded. Embedded commands are executed by the server
before it serves the page to the client (so serving HTML
pages containing embedded commands is slower than serving
straight HTML pages). Embedded pages can be processed either
by an Apache module or a CGI program. Using a module will be
much faster. Languages available for embedded use include
SSI, PHP, Perl and NeoScript (of these, SSI is built into
Apache by default, while the others require a new module to
be compiled in).
The alternative to embedding the commands into HTML is to
write self-contained programs. These usually use the
CGI, or Common Gateway Interface, to work with the
server. The CGI
specification says how servers should talk to the script
or program and how the script or program formats its reply
for use by the server. CGI is not a language itself.
If you know the CGI protocol you can write programs for use
with a web server in any language.
If you want better performance from your pages (by
performance we mean low use of resources, resulting in more
pages served more quickly), you should use either a
pre-compiled language (such as C) and CGI, or a scripting
language which is available as an Apache module. In the case
of the perl and python modules, preload scripts or data that
will be used often. If you are thinking of using CGI, you
might consider using FastCGI instead. FastCGI
is an alterative method of running programs from a server
which has several new features and is more efficient than
normal CGI. If your CGI is in perl, think about using mod_perl to pre-load the
perl scripts (and, where possible, to open database and
similar connections when Apache starts and re-use them across
Of course the best performance can be obtained by using
static pages instead of dynamic ones. You might consider
pre-generating HTML files, rather than serving up dynamic
pages if possible. For example, if your readers access pages
from a database, it might be faster to export those pages
into HTML every so often, rather than lookup the records in
the database for every request.
Alternatively (or in addition) consider using a local cache
in front of your Apache server. The client would connect to
the cache first, and if that page has already recently been
requested, the cache would return it without calling the
server. This sort of local cache is also called a "server
accelerator". Your dynamic pages will have to be set up to
allow them to be cached though (SSI pages, for example, are
usually not cacheable).
Security is a very important considerable when thinking about
dynamic pages. All CGI programs, both scripted and compiled,
are potentially insecure. You have to be very careful when
writing CGI programs, for instance, to ensure that Internet
users cannot execute programs on your server or read files
they should not have access to.
Another security issue which might be important is related to
other local users. For example, you might want to let your
customers or colleagues use a dynamic language. But if you
let them write CGI programs they could write a program which
accesses other people's files (since by default all CGI
programs run as the same user). More limited scripted
languages (such as SSI) might be safer in this situation.
Dynamic Page Languages
Finally, here is a reference list of ways of including
dynamic pages on your site.
Traditional "Server Side Includes" allow simple dynamic
pages. Apache 1.2 extends SSI to include variables and
conditional code. Already part of Apache. Because of the
restricted range of commands this can be more secure than
other languages, and Apache has the ability to turn off
some less secure features.
A more comprehensive embedded language than SSI, with
built-in support for many databases (such as mSQL, mySQL,
DBM), page counters.
An embedded scripting language based on Tcl.
An extended version of SSI.
Python is an interpreted object-orientated language. This
module builds the Python interpreter into Apache for
better performance than normal CGI.
Perl is a powerful general purpose interpreted
(scripting) language. This module lets you embed
arbitrary Perl commands into your HTML.
Perl is an advanced interpreted language. This very
powerful module integrates Perl into Apache, letting you
pre-load Perl scripts, re-use resource across multiple
requests, and even write whole Apache modules in Perl.
This gives you much more access to and control over the
server than CGI programs in Perl (which this module also
supports). The ability to write modules in perl makes it
possible to extend the server's functionality relatively
easily, without the complexity of writing a module in C.
Compiled languages (C, Pascal, Fortran, etc)
Facilities available depend on language. Usually more
efficient than scripted or embedded languages. Has to be
written to use CGI protocol, or an equivalent such as
Scripting languages (Perl, Python, shell, etc)
For Some Languages
Facilities available depend on language. Unless an Apache
module is available, has to be written to use CGI
protocol. When using CGI is less efficient that compiled
languages or scripting languages using an Apache module.
(Note: * Perl can be embedded if eperl or mod_perl is
Use mod_jserv to
call Java "servlets" from Apache.
It is impossible to recommend the "best" dynamic page
language since what is best will depend on your needs.
However some general conclusions can be drawn.
If you do not already know a scripting or programming
language, use one of the embedded languages. SSI is probably
the simplest, but PHP has some useful extra features.
If you want a language than is quick to develop in and
efficient, use an embedded language such as PHP or embedded
perl, or use perl with mod_perl. If you prefer other
scripting languages, use one with an Apache module (e.g.
python). If you already use perl CGI programs, consider
moving over to using mod_perl, which will give you much
better performance and more control over the server.
If you want a "full" programming language for arbitary
programs, either use any compiled language (e.g. C) or use
perl with the perl module. If you've been put off Perl
because of concerns about performance, think again. The
module makes it very efficient, and the ease of development
and large range of add-on perl modules (packages) make
developing applications more convenient. To make external CGI
programs more efficient, use FastCGI instead of CGI, or write
in Perl and use mod_perl. For Java programs, use mod_jserv.
The final way to make a top-performance dynamic page is to
write an Apache module. This is complex and requires care to
ensure that you do not "leak" resources or affect the rest of
the server, but will give the best performance. Modules have
to be written in C (although it might be possible to
link in other languages). An alternative to writing modules
in C is to use mod_perl, which lets you develop Apache
modules in perl.
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