4.5 Validating the Configuration Syntax

Before you restart a server on a live production machine after the configuration has been changed, it's essential to validate that the configuration file is not broken. If the configuration is broken, the server won't restart and users will find your server offline for the time it'll take you to fix the configuration and start the server again.

You can use apachectl configtest or httpd -t to validate the configuration file without starting the server. You can safely validate the configuration file on a running production server, as long as you run this test before you restart the server with apachectl restart. Of course, it is not 100% perfect, but it will reveal any syntax errors you might have made while editing the file.

The validation procedure doesn't just parse the code in startup.pl, it executes it too. <Perl> sections invoke the Perl interpreter when reading the configuration files, and PerlRequire and PerlModule do so as well.

Of course, we assume that the code that gets called during this test cannot cause any harm to your running production environment. If you're worried about that, you can prevent the code in the startup script and in <Perl> sections from being executed during the syntax check. If the server configuration is tested with -Dsyntax_check:

panic% httpd -t -Dsyntax_check

you can check in your code whether syntax_check was set with:

Apache->define('syntax_check')

If, for example, you want to prevent the code in startup.pl from being executed, add the following at the top of the code:

return if Apache->define('syntax_check');

Of course, there is nothing magical about using the string 'syntax_check' as a flag—you can use any other string as well.