Controlling the log level of your application

5/3/2023

In this blog post, we will have a look at the different log levels and how to control them.

appsettings.json

If you just created a new ASP.NET Core project, you will find a file called appsettings.json in the root of your project. This file contains a section called Logging, which is used to configure the logging behavior of your application. The default configuration looks like this:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
    }
  }
}

Here you can control your default log level and the log level of specific namespaces. The default log level is used for all namespaces that are not explicitly configured. In the example above, the default log level is set to Information and the log level of the Microsoft.AspNetCore namespace is set to Warning. So when you use logger.LogWarning in your code, it will be logged, but when you use logger.LogInformation it will not be logged.

Custom objects

Let's assume you have a class like this:

namespace MyDomain;

public class MyClass
{
    private readonly ILogger<MyClass> _logger;

    public MyClass(ILogger<MyClass> logger)
    {
        _logger = logger;
    }

    public void Do()
    {
        _logger.LogDebug("Hey");
    }
}

Normally if you call Do it will not be logged, because the default log level is Information. But with the following LogLevel inside the appsettings.json file, it will be logged:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "MyDomain": "Debug"
    }
  }
}

The terminal will show:

dbug: MyDomain.MyClass.Do[0]
      Hey

So as long as your full qualified class name is part of the configured namespace inside the appsettings.json file, it will override the default log level. The logger will take the most specific log level. So if you have a class called MyDomain.MyClass and you configure the log level for MyDomain and MyDomain.MyClass, the log level for MyDomain.MyClass will be used.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "MyDomain": "Debug",
      "MyDomain.MyClass": "Warning"
    }
  }
}

In this case, Do will not log anything out.

Conclusion

In this blog post, we have seen how to control the log level of your application. You can configure the default log level and the log level of specific namespaces. The logger will take the most specific log level. So if you have a class called MyDomain.MyClass and you configure the log level for MyDomain and MyDomain.MyClass, the log level for MyDomain.MyClass will be used.

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