serilog 动态更新日志级别

使用这个库，更新配置文件，就可以动态更新 日志输出级别。

new LoggerConfiguration().ReadFrom.Configuration(hostingContext.Configuration)

这个Configuration 定义在这儿。

return settingConfiguration.Settings(
                new ConfigurationReader(
                    configuration.GetSection(sectionName),
                    assemblyFinder,
                    configuration));

进到这个 reader 里面，有 实现接口的方法：这个 Configure method 会在 上面的方法直接调用。

public void Configure(LoggerConfiguration loggerConfiguration)
        {
            ProcessLevelSwitchDeclarations();
            ProcessFilterSwitchDeclarations();

            ApplyMinimumLevel(loggerConfiguration);
            ApplyEnrichment(loggerConfiguration);
            ApplyFilters(loggerConfiguration);
            ApplyDestructuring(loggerConfiguration);
            ApplySinks(loggerConfiguration);
            ApplyAuditSinks(loggerConfiguration);
        }

其中有ApplyMinimumLevel， 这是设置日志级别的地方：

这下面会调用 ChangeToken.OnChange... 

that is when IConfiguration changed, a delegate will be trigger.

and this will change the LoggerConfiguration's MinimumLevel.ControlledBy(levelSwitch)

so below code also can change the level dynamicly:

public static LoggingLevelSwitch loggingLevelSwitch = new LoggingLevelSwitch();
        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureLogging((hostingContext, loggingBuilder) =>
                {

                    Log.Logger = new LoggerConfiguration()
                        .MinimumLevel.ControlledBy(loggingLevelSwitch)
                        .WriteTo.Console()
                        .CreateBootstrapLogger();
                    
                    loggingBuilder.ClearProviders();
                    loggingBuilder.AddSerilog();
                })
                .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); });

we can change the level at any time without the application restarting.