Hackery

Multiple Blosxom Instances

Mon 22 Oct 2007

The blosxom SourceForge developers have been foolish enough to give me a commit bit, so I've been doing some work lately on better separating code and configuration, primarily with a view to making blosxom easier to package.

One of the consequences of these changes is that it's now reasonably easy to run multiple blosxom instances on the same host from a single blosxom.cgi executable.

A typical cgi apache blosxom.conf might look something like this:

SetEnv BLOSXOM_CONFIG_DIR /etc/blosxom
Alias /blog /usr/share/blosxom/cgi
<Directory /usr/share/blosxom/cgi>
  DirectoryIndex blosxom.cgi
  RewriteEngine on
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteRule ^(.*)$ /blog/blosxom.cgi/$1 [L,QSA]
  <FilesMatch "\.cgi$">
    Options +ExecCGI
  </FilesMatch>
</Directory>

The only slightly tricky thing here is the use of mod_rewrite to allow the blosxom.cgi part to be omitted, so we can use URLs like:

http://www.example.com/blog/foo/bar

instead of:

http://www.example.com/blog/blosxom.cgi/foo/bar

That's nice, but completely optional.

The SetEnv BLOSXOM_CONFIG_DIR setting is the important bit for running multiple instances - it allows you to specify a location blosxom should look for all its configuration settings. If we can set this multiple times to different paths we get multiple blosxom instances quite straightforwardly.

With separate virtual hosts this is easy - just put the SetEnv BLOSXOM_CONFIG_DIR inside your virtual host declaration and it gets scoped properly and everything just works e.g.

<VirtualHost *:80>
ServerName bookmarks.example.com
DocumentRoot /usr/share/blosxom/cgi
AddHandler cgi-script .cgi
SetEnv BLOSXOM_CONFIG_DIR '/home/gavin/bloglets/bookmarks/config'
<Directory /usr/share/blosxom/cgi>
  DirectoryIndex blosxom.cgi
  RewriteEngine on
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteRule ^(.*)$ /blosxom.cgi/$1 [L,QSA]
  <FilesMatch "\.cgi$">
    Options +ExecCGI
  </FilesMatch>
</Directory>
</VirtualHost>

It's not quite that easy if you want two instances on same virtual host e.g. /blog for your blog proper, and /bookmarks for your link blog. You don't want the SetEnv to be global anymore, and you can't put it inside the <Directory> section either since you can't repeat that with a single directory.

One solution - the hack - would be to just make another copy your blosxom.cgi somewhere else, and use that to give you two separate directory sections.

The better solution, though, is to use an additional <Location> section for each of your instances. The only extra wrinkle with this is if you're using those optional rewrite rules, in which case you have to duplicate and further qualify them as well, since the rewrite rule itself is namespaced i.e.

Alias /blog /usr/share/blosxom/cgi
Alias /bookmarks /usr/share/blosxom/cgi
<Directory /usr/share/blosxom/cgi>
  DirectoryIndex blosxom.cgi
  RewriteEngine on
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_URI} ^/blog
  RewriteRule ^(.*)$ /blog/blosxom.cgi/$1 [L,QSA]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_URI} ^/bookmarks
  RewriteRule ^(.*)$ /bookmarks/blosxom.cgi/$1 [L,QSA]
  <FilesMatch "\.cgi$">
    Options +ExecCGI
  </FilesMatch>
</Directory>
<Location /blog>
  SetEnv BLOSXOM_CONFIG_DIR /home/gavin/blog/config
</Location>
<Location /bookmarks>
  SetEnv BLOSXOM_CONFIG_DIR /home/gavin/bloglets/bookmarks/config
</Location>

Because one blosxom just ain't enough ...