Best practice to include log4Net external config file in ASP.NET

Question

I have seen at least two ways to include an external log4net config file in an ASP.NET web application:

Having the following attribute in your AssemblyInfo.cs file:

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log.config", Watch = true)]

Calling the XmlConfigurator in the Global.asax.cs:

protected void Application_Start()
{
    XmlConfigurator.Configure(new FileInfo("Log.config"));
}

What would be the best practice to do it?

Answer 1

At startup, call:

XmlConfigurator.Configure();

In your Web.config, specify log4net.Config in appSettings:

<add key="log4net.Config" value="Log.config" />

This special setting allows you to change the log configuration without having to recompile. Especially helpful for moving between multiple environments.

Example

Consider the following project file structure:

\config\log4net\debug.config
\config\log4net\staging.config
\config\log4net\release.config
\config\appSettings\debug.config
\config\appSettings\staging.config
\config\appSettings\release.config

Application and logging configurations are distinguished for each environment. References to the logging configurations are maintained in the application settings.

\config\appSettings\debug.config:

<appSettings>
    <add key="log4net.Config" value="config\log4net\debug.config" />
    ...
</appSettings>

\config\appSettings\staging.config:

<appSettings>
    <add key="log4net.Config" value="config\log4net\staging.config" />
    ...
</appSettings>

\config\appSettings\release.config:

<appSettings>
    <add key="log4net.Config" value="config\log4net\release.config" />
    ...
</appSettings>

Changing environments is a simple matter of updating the appSettings file in Web.config.

<appSettings file="config\appSettings\staging.config">
    ...
</appSettings>

Answer 2

I was dissatisfied with the "magic" configuration approach, because I wanted to specify my configuration in a path with an environment variable (%PUBLIC%\MyApp\MySettings.config).

So instead, I have this in my app.config:

<add key="MyLog4NetConfigFile" value="%PUBLIC%\MyApp\MySettings.config"/>

And do this to set my log4net configuration:

var configFile = ConfigurationManager.AppSettings.Get("MyLog4NetConfigFile");
if( !string.IsNullOrEmpty(configFile))
{
    configFile = Environment.ExpandEnvironmentVariables(configFile);
    XmlConfigurator.Configure(new FileInfo(configFile));
}