The GELF module requires the GELF PHP library.
To install, use one of the following methods:
-
Checkout the GELF PHP library from github like so:
git clone https://github.com/Graylog2/gelf-php.git sites/all/libraries/gelf-php
-
Install via Drush
drush gelf-download
Older versions of the GELF PHP library contained the file 'gelf.php'. Newer versions have split that out into GELFMessage.php and GELFMessagePublisher.php. If your instance of gelf-php doesn't have those two newer files, you probably need to do a 'git pull' in the gelf-php directory to get the latest version.