Surface Program class logging pattern

aspnetcore/fundamentals/logging/index.md

@@ -5,7 +5,7 @@ description: Learn how to use the logging framework provided by the Microsoft.Ex
 monikerRange: '>= aspnetcore-2.1'
 ms.author: riande
 ms.custom: mvc
-ms.date: 10/08/2019
+ms.date: 11/05/2019
 uid: fundamentals/logging/index
 ---
 # Logging in .NET Core and ASP.NET Core
@@ -125,6 +125,69 @@ To write logs in the `Program` class of an ASP.NET Core app, get an `ILogger` in
 
 [!code-csharp[](index/samples/3.x/TodoApiSample/Program.cs?name=snippet_LogFromMain&highlight=9,10)]
 
+Logging during host construction isn't directly supported. However, a separate logger can be used. In the following example, a [Serilog](https://serilog.net/) logger is used to log in `CreateHostBuilder`. `AddSerilog` uses the static configuration specified in `Log.Logger`:
+
+```csharp
+using System;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+public class Program
+{
+    public static void Main(string[] args)
+    {
+        CreateHostBuilder(args).Build().Run();
+    }
+
+    public static IHostBuilder CreateHostBuilder(string[] args)
+    {
+        var builtConfig = new ConfigurationBuilder()
+            .AddJsonFile("appsettings.json")
+            .AddCommandLine(args)
+            .Build();
+
+        Log.Logger = new LoggerConfiguration()
+            .WriteTo.Console()
+            .WriteTo.File(builtConfig["Logging:FilePath"])
+            .CreateLogger();
+
+        try
+        {
+            return Host.CreateDefaultBuilder(args)
+                .ConfigureServices((context, services) =>
+                {
+                    services.AddRazorPages();
+                })
+                .ConfigureAppConfiguration((hostingContext, config) =>
+                {
+                    config.AddConfiguration(builtConfig);
+                })
+                .ConfigureLogging(logging =>
+                {   
+                    logging.AddSerilog();
+                })
+                .ConfigureWebHostDefaults(webBuilder =>
+                {
+                    webBuilder.UseStartup<Startup>();
+                });
+        }
+        catch (Exception ex)
+        {
+            Log.Fatal(ex, "Host builder error");
+
+            throw;
+        }
+        finally
+        {
+            Log.CloseAndFlush();
+        }
+    }
+}
+```
+
 ### Create logs in the Startup class
 
 To write logs in the `Startup.Configure` method of an ASP.NET Core app, include an `ILogger` parameter in the method signature:
@@ -162,6 +225,66 @@ To write logs in the `Program` class, get an `ILogger` instance from DI:
 
 [!code-csharp[](index/samples/2.x/TodoApiSample/Program.cs?name=snippet_LogFromMain&highlight=9,10)]
 
+Logging during host construction isn't directly supported. However, a separate logger can be used. In the following example, a [Serilog](https://serilog.net/) logger is used to log in `CreateWebHostBuilder`. `AddSerilog` uses the static configuration specified in `Log.Logger`:
+
+```csharp
+using System;
+using Microsoft.AspNetCore;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging;
+
+public class Program
+{
+    public static void Main(string[] args)
+    {
+        CreateWebHostBuilder(args).Build().Run();
+    }
+
+    public static IWebHostBuilder CreateWebHostBuilder(string[] args)
+    {
+        var builtConfig = new ConfigurationBuilder()
+            .AddJsonFile("appsettings.json")
+            .AddCommandLine(args)
+            .Build();
+
+        Log.Logger = new LoggerConfiguration()
+            .WriteTo.Console()
+            .WriteTo.File(builtConfig["Logging:FilePath"])
+            .CreateLogger();
+
+        try
+        {
+            return WebHost.CreateDefaultBuilder(args)
+                .ConfigureServices((context, services) =>
+                {
+                    services.AddMvc();
+                })
+                .ConfigureAppConfiguration((hostingContext, config) =>
+                {
+                    config.AddConfiguration(builtConfig);
+                })
+                .ConfigureLogging(logging =>
+                {
+                    logging.AddSerilog();
+                })
+                .UseStartup<Startup>();
+        }
+        catch (Exception ex)
+        {
+            Log.Fatal(ex, "Host builder error");
+
+            throw;
+        }
+        finally
+        {
+            Log.CloseAndFlush();
+        }
+    }
+}
+```
+
 ::: moniker-end
 
 ### No asynchronous logger methods