One PHP error log per developer

At work we’re using a shared web development server, with a setup that allows every developer to have his own compartmentalized development space. It requires some tricky configurations, but in the end I find it way more efficient than the policy “every developer installs its own Apache/PHP/MySQL stack”. I already talked about the general ideas in a previous article (in french) two years ago, and so far it works like a charm. Our setup it constantly improving, and today’s big question is: how to make so that every developer has it’s own PHP error log?

Apache config

First, a little insight on the Apache configuration. If we would be using one virtual host directive per developer, this wouldn’t be an issue at all. Just set up the proper error_log path (using Apache’s php_value directive like so: php_value error_log /var/log/php/errors_username.log) for every virtual host, reload Apache and you’re done.

Our Apache, however, is using mod_vhost_alias. Basically we have “one virtual host to rule them all”, because I’m lazy and I don’t want to write one virtual host for every new dev, or modify a dozens of virtual host directives everytime I change a setting.

So how does it works? The first part of the URL is the developer username, then the second part is the project’s folder name, then the remaining part is the dev server hostname. With the VirtualDocumentRoot directive, you use parts of the URL has variable for calculating the correct document root path. (Actually, our setup includes a third part which is the subfolder to separate the document root of a project from all the include files, but that’s not the point of this article). Example:

<VirtualHost *:80>
	ServerName dev.domain.com
	ServerAlias *.dev.domain.com

	UseCanonicalName off
	VirtualDocumentRoot /home/%1/web/%2

	<Directory /home/*/web/*/*>
		Allow from all
		AllowOverride all
	</Directory>
</VirtualHost>

The address http://remi.awesome.dev.domain.com will automagically has a document root located in: /home/remi/web/awesome. The benefit is obvious: simplicity and flexibilty. I love convention over configuration design principle.

PHP config

Now the problem is that it’s impossible to tell PHP to logs the errors on a different file based on the first part of the URL directly into the Apache configuration, because the %1, %2,… variable are only valid inside the VirtualDocumentRoot directive.

So we need to do it inside PHP or inside an htaccess file on every folder. But doing it for every project is a pain, not to mention the conflicts to come in SVN because every developer will have his own path. That’s when PHP’s auto_prepend_file option come into play (and honestly, I would never have thought it’ll be useful one day).

I just create a file named /etc/php5/prepend.php with that one-liner:

<?php ini_set('error_log',sprintf('/var/log/php/errors_%s.log',substr($_SERVER['SERVER_NAME'], 0, strpos($_SERVER['SERVER_NAME'],'.'))));

And add this settings to php.ini:

auto_prepend_file = /etc/php5/prepend.php

Note that the directory /var/log/php will not be created out of the blue, so you have to take care of it, and it must be writeable by www-data. Files will be named errors_(first part of the url).log, so for example errors_remi.log in the previous example. Users belongs to group www-data, so as long as the logs are readable by the group (what they are by default) they’ll be able to read their logs.

And now the cherry on top of the cake, the logrotate configuration to rotate logs weekly, and keep one month (4 files) of archive:

/var/log/php/errors_*.log {
        weekly
        missingok
        rotate 4
        compress
        delaycompress
        notifempty
        create 640 www-data www-data
}

Et voilà!