ILoggerFactory vs serviceCollection.AddLogging vs WebHostBuilder.ConfigureLogging

问题

I have typical logging requirement for my asp.net core 2.x app:

• use application insight in production,
• console and debug logger in development env
• setup some filters based on category and log level

Now I see at least three different API's to configure the logging:

1. WebHostBuilder.ConfigureLogging()in Program.cs

   public static void Main(string[] args)
   {
       var webHost = new WebHostBuilder()               
           .ConfigureLogging((hostingContext, logging) =>
           {
               logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
               logging.AddConsole();
               logging.AddDebug();
               logging.AddAzureWebAppDiagnostics();
           })
           .UseStartup<Startup>()
           .Build();
   
       webHost.Run();
   }
   

2. Inject ILoggerFactory to Startup.Configure method:

   public void Configure(IApplicationBuilder app, ILoggerFactory loggerFactory, IServiceProvider serviceProvider)
   {
       loggerFactory.AddConsole();
       loggerFactory.AddAzureWebAppDiagnostics();
       loggerFactory.AddApplicationInsights(app.ApplicationServices, 
           (category, level) => level >= (category == "Microsoft" ? LogLevel.Error : LogLevel.Information));
       }
   

3. in Startup.ConfigureServices:

   public void ConfigureServices(IServiceCollection services)
   {
       services.AddLogging(logging => 
       {
           logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
           logging.AddConsole();
           logging.AddDebug();
           logging.AddAzureWebAppDiagnostics();
       }
   }
   

What is the difference between those? When to use which?

回答1:

The third one use ConfigureServices which is a public method in the WebHostBuilder. And the first one use ConfigureLogging which is one of IHostBuilder's extension method in HostingHostBuilderExtensions.

And they both call the IServiceCollection's extension method AddLogging in LoggingServiceCollectionExtensions under Microsoft.Extensions.Logging package. The AddLogging method first try to add two singleton ILoggerFactory and ILogger<> and an enumerable of LoggerFilterOptions. Then do the action for logging(ILoggingBuilder) which finally calls AddProvider method to add the log providers implemented by these providers(Console, Azure) and calls SetMinimumLevel to add LoggerFilterOptions

The second method directly adds the log providers to LoggerFactory. And these providers are called in LoggerFactory when logging methods are called.

As for orders, the second and third methods are called by WebHostBuilder's UseStartup<TStartup> method.

来源：https://stackoverflow.com/questions/50744024/iloggerfactory-vs-servicecollection-addlogging-vs-webhostbuilder-configureloggin