Logging with log4net

This topic provides developers and system administrators with an introduction to the standard implementation of the Logging API using log4net in the Episerver platform, including CMS and Commerce. It describes how to configure logging in Episerver, and how to interpret the logged information, plus some best practices.  When you deploy the EPiServer.Logging.Log4Net package in your solution, any logging by the system uses the log4net framework.  

Note: You should read the introduction at the Log4net website for a better understanding before reading this topic.

Logging levels

The following levels of logging are assigned according to priority level, with OFF having the highest value and ALL the lowest value:

1. OFF
2. FATAL
3. ERROR
4. WARN
5. INFO
6. DEBUG
7. ALL

Enabling logging

You control logging from EPiServerLog.config. Place it in the same directory as the application’s web.config file. The logging configuration is separated from web.config in case you want to enable logging when the application has entered a bad state and you have to change and save the configuration file. If the information is in web.config, the web application is restarted when you save web.config, possibly clearing the cause for the problem that you wanted to log. Keeping the log configuration separate from web.config eliminates this problem.

A very simple log configuration file may look like this:

<log4net>
   <appender name="ErrorAppender" type="log4net.Appender.FileAppender" >
      <file value="e:\\episerverlogfiles\\log-file.txt" />
      <appendToFile value="true" />
      <layout type="log4net.Layout.PatternLayout">
         <conversionPattern value="%d [%t] %l - %m%n" />
      </layout>
   </appender>
   <root>
       <level value="WARN" />
       <appender-ref ref="ErrorAppender" />
   </root>
</log4net>

If you want to enable full logging, simply change the level value in the root tag to ALL; this gives you a lot of data.

Disabling logging

You have the following ways to disable active logging:

• Set the level to OFF in EPiServerLog.config.
• Remove the file and restart the website by saving the system settings/web.config again, killing the process, or resetting IIS. It is not enough to just remove the file because the website must be restarted to disable logging.

Logging site information

The site information is primarily concerned with logging various problems and unusual events. Basically you should always monitor events with log level WARN and above. Events with lower levels are primarily intended to get information to track down specific errors and/or bugs. A developer might want to enable full logging to a RollingFileAppender (see the log4net documentation) in the development environment to check what has happened in Episerver if a specific problem occurs. However, during regular production use, you would probably want to just monitor WARN events and higher.

Exceptions are logged with the complete stack trace to let you track down exception errors. Be aware that exceptions are expensive in terms of performance. Avoid writing code that generates exceptions as part of the normal program flow.

Organizing log file storage

For a production site, it is essential to have a policy regarding log files to avoid problems, such as exposing log files on your website, filling up a system partition with log data, and so on. The Episerver logging functions are intended to monitor the health of your web application and should not (under normal operation) cause excessive logging, as long as you do not enable logging of events below the WARN level. 

Note: If you are using remoting, UDP appenders or any type of appender that does not write log files to the local drives, the actual storage of log data will probably not happen on the web server, although other restrictions may apply.

• Store log files outside the folder structure exposed by the web server. This means that if your EPiServer CMS application is installed in the C:\EPiServer\EPiServerSite1 folder, do not store your log files in the C:\EPiServer\EPiServerSite1\App_Data folder (default storage). Depending on web server configuration and file access rights, this could expose your logs to any visitor to your website.
• Do not store log files on the system partition. This means that if your web server has the operating system installed on the C: drive, store the log files on another drive. Even though Episerver’s log functions should not cause large log files during normal operation, the log files may grow very large if you enable full debugging. If the logging takes all free space on your system partition, you will experience a range of problems, most likely making your website unavailable until the situation is resolved.

Related topics

• Logging API in Episerver
• About the log4net framework