How can I forward IIS logs to a syslog deamon?

Friday, October 4th, 2002

How can I forward IIS logs to a syslog deamon?

Created on 2002-10-04 by Rainer Gerhards.

MonitorWare Agent can forward Microsoft Internet Information Server (IIS) log files to any syslog deamon (or syslo server, if you like). Fortunately, IIS stores web log files as plain text files in the file system. Even better, other processes are allowed to read these files while IIS adds information to them. This enables MonitorWare Agent to forward them in near real-time.

MonitorWare Agent’s file monitor is optimized to pick up application log files. This includes IIS log files. Specific logic enables it to gather only the valid part of the currently being written log file (IIS writes files in 64K increments and there is garbage after the valid log data lines). Special replacement characters inside the file name allow to handle changing file names, so monitoring even works while rolling over to new names.

To activate log forwarding, create one file monitor per IIS log file to monitor. Be sure to use the proper replacement characters if IIS modifies the log file name (by default, it includes the day of month). Details on them can be found in the manual. Then be sure to send all file lines to a rule base that has syslog forwarding enabled. There is a sample in the Step-By-Step Guides inside the manual.

IIS log file data is like any other event data in MonitorWare Agent. So it can not only be forwarded by syslog but also be filtered, acted on, alerts generated and so on. Another possible approach is to generate alerts if specific attack patterns show up in the logs. As long as the pattern is known and can be seen in the log file line, this can easily be configured.

Just a reminder: besides IIS, all other text logs can be processed. Prominent examples include the DHCP log or database message log files.