Musings on a Multiblog WordPress

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Update June 2007: Try WordPress Multi-User now.

I’ve used Shelley’s instructions using soft links. I tried Rubén’s proof-of-concept, but got stuck somewhere in the middle.

So I started thinking: how can we go about making WordPress MultiBlog-capable? Here is a rough transcript of my thoughts (I’ve removed some of the dead ends and hesitations) in the hope that they might contribute to the general resolution of the problem. I have to point out my position here: somebody with a dedicated server who’s thinking of setting up a “WordPress weblog-farm” (for my pupils, mainly). So I’m aware that I’m not the “standard user” and that my solution is going to be impractical to many. But hey, let’s see where it leads, all the same. Actually, I think I probably reconstructed most of Rubén’s strategy here — but I’m not sure to what extent what I suggest differs from what he has done.

From a system point of view, we want to have a unique installation of WordPress, and duplication of only the files which are different from one blog to another (index.php, wp-config.php, wp-comments.php, wp-layout.css, to name a few obvious ones). The whole point being that when the isntall needs to be upgraded, it only has to be upgraded in one place. When a plugin is downloaded and installed, it only has to be done once for all weblogs — though it can of course be activated individually for each weblog.

From the point of view of the weblogs themselves, they need to appear to be in different domains/subdomains/folders/whatever. What I’m most interested in is different subdomains, so I’ll stick to that in my thinking. (Then somebody can come and tell me that my “solution” doesn’t work for subfolders, and here’s one that works for subfolders and subdomains, and we’ll all be happy, thankyouverymuch.) So, when I’m working with blog1.example.com all the addresses need to refer to that subdomain (blog1.example.com/wp-admin/, etc); ditto for blog2.example.com, blog3.example.com, blogn.example.com (I used to like maths in High School a lot).

As Rubén puts it, the problem with symbolic links (”soft links”) is called “soft link hell”: think of a great number of rubber bands stretched all over your server. Ugh. So let’s try to go in his direction, for a while. First, map all the subdomains to the same folder on the server. Let’s say blog1.example.com, blog2.example.com (etc.) all point to /home/bunny/www/wordpress/. Neat, huh? Not so. They will all use the same wp-config.php file, and hence all be the same weblog.

This is where Rubén’s idea comes in: include a file at the top of wp-config.php which:

1. identifies which blog we are working with (in my case, by parsing $HTTP_HOST, for example — there might be a more elegant solution)
2. “replaces” the files in the master installation directory by the files in a special “blog” directory, if they exist

The second point is the tricky one, of course. We’d probably have a subfolder per blog in wordpress/blogs: wordpress/blogs/blog1, wordpress/blogs/blog2, etc. The included file would match the subdomain string with the equivalent folder, check if the page it’s trying to retrieve exists in the folder, and if it does, include that one and stop processing the initial script after that. Another (maybe more elegant) option would be to do some Apache magic (I’m dreaming, no idea if it’s possible) to systematically check if a file is available in the subdirectory matching the subdomain before using the one in the master directory. Anybody know if this is feasible?

The problem I see is with includes. We have (at least) three types of include calls:

• include (ABSPATH . 'wp-comments.php');
• require ('./wp-blog-header.php');
• require_once(dirname(__FILE__).'/' . '/wp-config.php');

As far as I see it, they’ll all break if the calling include is in /home/bunny/www/wordpress/blogs/blog1 and the file to be called is in /home/bunny/www/wordpress. What is wrong with relative includes? Oh, they would break too. Dammit.

We would need some intelligence to determine if the file to be included or called exists in the subdirectory or not, and magically adapt the include call to point to the “right” file. I suspect this could be done, but would require modifying all (at least, a lot of) the include/requires in WordPress.

Maybe another path to explore would be to create a table in the database to keep track of existing blogs, and of the files that need to be “overridden” for each blog. But again, I suspect that would mean recoding all the includes in WordPress.

Another problem would be .htaccess. Apache would be retrieving the same .htaccess for all subdomains, and that happens before PHP comes into play, if I’m not mistaken.

Any bright ideas to get us out of this fix? Alternate solutions? Comments? Things I missed or got wrong? The comments and trackbacks are yours. Thanks for your attention.

Tagged as: apache, change, farm, folder, hack, htaccess, modify, multi, multiblog, multiple, multisite, server, site, subdomain, weblog, wordpress