Reverse Proxy to Make SPARQL Endpoint Available on Nice URI

When you set up an RDF repository such as Sesame2, you are likely to get a SPARQL endpoint at a URI such as http://my.server.org:8080/openrdf-sesame/repositories/repname. That's ok, but it doesn't look very nice. In order to serve the same endpoint at a nicer URI, say http://my.server.org/sparql, you can set up something called a reverse proxy on your Apache server. Here is how to do it on Debian:

Add the Reverse Proxy Rule

In /etc/apache2/conf.d, add a new configuration file sparql.conf. Make it look like this:

# Make the SPARQL endpoint of the Sesame server running on port 8080
# available as http://my.server.org/sparql.
#
# Configuration is done as per the Basic Example for Reverse Proxies
# in http://httpd.apache.org/docs/2.2/mod/mod_proxy.html .

<Proxy *>
 Order deny,allow
 Allow from all
</Proxy>
ProxyPass /sparql http://my.server.org:8080/openrdf-sesame/repositories/repname
ProxyPassReverse /sparql http://my.server.org:8080/openrdf-sesame/repositories/repname

Enable the Proxy Modules

In order for this to work, Apache has to load a number of modules having to do with proxies. The easiest and safest way to load them is by using the a2enmod command and select all proxy-related modules:

knumoe@exp3:/etc/apache2/conf.d$ sudo a2enmod
Your choices are: actions alias asis auth_basic auth_digest authn_alias authn_anon authn_dbd authn_dbm authn_default authn_file authnz_ldap authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cern_meta cgi cgid charset_lite dav dav_fs dav_lock dbd deflate dir disk_cache dump_io env expires ext_filter file_cache filter headers ident imagemap include info ldap log_forensic mem_cache mime mime_magic negotiation php5 proxy proxy_ajp proxy_balancer proxy_connect proxy_ftp proxy_http rewrite setenvif speling ssl status substitute suexec unique_id userdir usertrack version vhost_alias
Which module(s) do you want to enable (wildcards ok)?
proxy*

Restart Apache

sudo /etc/init.d/apache2 restart

WordPress Blank Screen of Death

I'm using subversion to keep my WordPress installation updated. This always worked perfectly fine, but recently I did an update and wasn't able to access any php driven part of the blog anymore (so, basically everything). All I would get is the dreaded WordPress Blank Screen of Death.

I looked in the error logs (WP had a special error log in the Apache log folder) and saw that there was a Parse Error: parse error, unexpected T_SL reported for one of the php files. After some googling, this post here made me realise that the problem could be related to a subversion conflict, which will lead to < signs showing up in the source files, rendering them invalid. I checked the offending files and really, it turned out that my last svn update had introduced a conflict. To resolve it, I simply deleted the offending files, executed svn update again, and all my troubles were gone!

Let Regular Web Sites Coexist with a CMS like Drupal

I have a server setup where I want Drupal (could be any other CMS, though) to be served from the document root. I.e., I don't want a URL like http://my.server/drupal/interesting-page, but instead I want http://my.server/interesting-page. This is easy to achieve in Apache2: I simply have to set the document root to the Drupal folder. Here is an example from an Apache2 configuration file:

  <VirtualHost *>
  ...
  DocumentRoot /var/www/drupal
  <Directory />
    Options FollowSymLinks
    AllowOverride None
  </Directory>
  <Directory /var/www/drupal>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride all
    Order allow,deny
    allow from all
  </Directory>
  ...
  </VirtualHost>

Another requirement I have is that certain folders should be served alongside Drupal. E.g., let's assume I have a folder called dumps, which I want to serve at http://my.server/dumps. Now, I could of course just put it into the drupal folder at /var/www/drupal/dumps. However, I would like the drupal folder to only contain drupal stuff. Otherwise things might get messy when I do updates, etc. This is where the Alias directive in Apache's mod_alias module comes in handy. I can put dumps at /var/www/dumps and then map requests to http://my.server/dumps to that folder. Here is what that looks like in my Virtual Host definition (including some settings for how to handle that folder):

Alias /dumps "/var/www/dumps"
<Directory "/var/www/dumps">
  Options Indexes MultiViews
  AllowOverride None
  Order deny,allow
  Allow from all
</Directory>

Installing Drupal6.4 on Debian4 + Apache2

I had to install Drupal today on one of our servers. I ran into a few minor problems:

• There were some problems with file permissions in the drupal/sites folder, so I changed owner and group of some files and folders to www-data.
• Drupal complained that the PHP GD library is not installed: just run apt-get install php5-gd and restart Apache.
• Drupal couldn't send mails, so I installed postfix (sudo apt-get install postfix), set the server for outgoing mail (here called the "smart server") to our institute's smtp server, and used mailx to test it.