Defensive logging on ASP.NET Core

ASP.NET Core logging framework is intelligent one and it supports also so called defensive logging that helps us to have intelligent logs but still avoid putting additonal load to system when it’s not needed. This blog post is short overview of defensive logging on ASP.NET Core.

Defensive logging is supported by ASP.NET Core logging framework. Let’s suppose there’s some information-level logging code that asks additional information from service or data layer.

public IActionResult ConfirmOrder(int id)
{
    var order = _orderService.GetById(id);
 
    var user = _userService.GetById(User.Identity.Name);
    _logger.LogInformation("User " + user.FullName + " confirmed order " + order.OrderNo);
 
    ... //
}

Although the code forms a nice logging message with all information needed the message is useless when information level is not in use. Logging framework doesn’t throw any exceptions but message is not logged. Some expensive code is running on server but the outcome of it is nothing.

Let’s try now to avoid this situation and let’s write to log only if information level is allowed. For this ILogger provides IsEnabled() method.

public IActionResult ConfirmOrder(int id)
{
    var order = _orderService.GetById(id);
 
    if (_logger.IsEnabled(LogLevel.Information))
    {
        var user = _userService.GetById(User.Identity.Name);
        _logger.LogInformation("User " + user.FullName + " confirmed order " + order.OrderNo);
    }
 
    ... //
}

Now information-level message is created only when information-level logging is enabled. This code saves one expensive round-trip to service layer in production environment.

Wrapping up

ASP.NET Core logging framework provides us with intelligent logging options like defensive logging. For test and QA environments we can enable more logging and we can completely switch off same powerful logging code depending on if given log level is enabled.