restart_aspnet_app_domain.cs

// adapted from Umbraco and NopCommerce source

public static void RestartAppDomain()
{
    if (GetTrustLevel() > AspNetHostingPermissionLevel.Medium)
    {
        //full trust
        HttpRuntime.UnloadAppDomain();
        TryWriteWebConfig();
        TryWriteGlobalAsax();
    }
    else
    {
        //medium trust
        bool success = TryWriteWebConfig();
        if (!success)
        {
            throw new ApplicationException(
                "The application needs needs to be restarted due to a configuration change, but was unable to do so." +
                Environment.NewLine +
                "To prevent this issue in the future, a change to the web server configuration is required:" +
                Environment.NewLine +
                "- run the application in a full trust environment, or" + Environment.NewLine +
                "- give the application write access to the 'web.config' file.");
        }

        success = TryWriteGlobalAsax();
        if (!success)
        {
            throw new ApplicationException(
                "The application needs to be restarted due to a configuration change, but was unable to do so." +
                Environment.NewLine +
                "To prevent this issue in the future, a change to the web server configuration is required:" +
                Environment.NewLine +
                "- run the application in a full trust environment, or" + Environment.NewLine +
                "- give the application write access to the 'Global.asax' file.");
        }
    }
}

#region Private Methods

private static AspNetHostingPermissionLevel? _trustLevel = null;

/// <summary>
/// Finds the trust level of the running application (http://blogs.msdn.com/dmitryr/archive/2007/01/23/finding-out-the-current-trust-level-in-asp-net.aspx)
/// </summary>
/// <returns>The current trust level.</returns>
private static AspNetHostingPermissionLevel GetTrustLevel()
{
    if (!_trustLevel.HasValue)
    {
        //set minimum
        _trustLevel = AspNetHostingPermissionLevel.None;

        //determine maximum
        foreach (var trustLevel in
            new[]
            {
                AspNetHostingPermissionLevel.Unrestricted,
                AspNetHostingPermissionLevel.High,
                AspNetHostingPermissionLevel.Medium,
                AspNetHostingPermissionLevel.Low,
                AspNetHostingPermissionLevel.Minimal
            })
        {
            try
            {
                new AspNetHostingPermission(trustLevel).Demand();
                _trustLevel = trustLevel;
                break; //we've set the highest permission we can
            }
            catch (System.Security.SecurityException)
            {
                continue;
            }
        }
    }
    return _trustLevel.Value;
}

private static bool TryWriteWebConfig()
{
    try
    {
        //Do an explicit write
        var webConfigFile = MapPath("~/web.config");
        var contents = File.ReadAllText(webConfigFile);
        contents = contents.Substring(0, contents.IndexOf("</configuration>", StringComparison.OrdinalIgnoreCase) + 16) + "\n<!-- restart at " + DateTime.Now.ToString("u") + " -->";
        File.WriteAllText(webConfigFile, contents);

        //File.SetLastWriteTimeUtc(webConfigFile, DateTime.UtcNow);
        return true;
    }
    catch
    {
        return false;
    }
}

private static bool TryWriteGlobalAsax()
{
    try
    {
        File.SetLastWriteTimeUtc(MapPath("~/global.asax"), DateTime.UtcNow);
        return true;
    }
    catch
    {
        return false;
    }
}

#endregion