netstandard2.1 only, update to Serilog.Extensions.Hosting 4.0.0 to pull in CreateBootstrapLogger(), one sample (showing two-stage intialization), simplified README

Author: nblumhardt

README.md

@@ -22,7 +22,6 @@ public class Program
     public static int Main(string[] args)
     {
         Log.Logger = new LoggerConfiguration()
-            .MinimumLevel.Debug()
             .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
             .Enrich.FromLogContext()
             .WriteTo.Console()
@@ -81,7 +80,7 @@ That's it! With the level bumped up a little you will see log output resembling:
 
 **Tip:** to see Serilog output in the Visual Studio output window when running under IIS, either select _ASP.NET Core Web Server_ from the _Show output from_ drop-down list, or replace `WriteTo.Console()` in the logger configuration with `WriteTo.Debug()`.
 
-A more complete example, showing `appsettings.json` configuration, can be found in [the sample project here](https://github.com/serilog/serilog-aspnetcore/tree/dev/samples/EarlyInitializationSample).
+A more complete example, including `appsettings.json` configuration, can be found in [the sample project here](https://github.com/serilog/serilog-aspnetcore/tree/dev/samples/Sample).
 
 ### Request logging
 
@@ -188,59 +187,73 @@ app.UseSerilogRequestLogging(options =>
 });
 ```
 
-### Inline initialization
+### Two-stage initialization
 
-You can alternatively configure Serilog inline, in `BuildWebHost()`, using a delegate as shown below:
+The example at the top of this page shows how to configure Serilog immediately when the application starts. This has the benefit of catching and reporting exceptions thrown during set-up of the ASP.NET Core host.
 
-```csharp
-    .UseSerilog((hostingContext, services, loggerConfiguration) => loggerConfiguration
-        .ReadFrom.Configuration(hostingContext.Configuration)
-        .Enrich.FromLogContext()
-        .WriteTo.Console())
-```
+The downside of initializing Serilog first is that services from the ASP.NET Core host, including the `appsettings.json` configuration and dependency injection, aren't available yet.
 
-This has the advantage of making a service provider and the `hostingContext`'s `Configuration` object available for [configuration of the logger](https://github.com/serilog/serilog-settings-configuration), but at the expense of losing `Exception`s raised earlier in program startup.
+To address this, Serilog supports two-stage initialization. An initial "bootstrap" logger is configured immediately when the program starts, and this is replaced by the fully-configured logger once the host has loaded.
 
-If this method is used, `Log.Logger` is assigned implicitly, and closed when the app is shut down.
+To use this technique, first replace the initial `CreateLogger()` call with `CreateBoostrapLogger()`:
 
-A complete example, showing this approach, can be found in [the _InlineIntializationSample_ project](https://github.com/serilog/serilog-aspnetcore/tree/dev/samples/InlineInitializationSample).
+```csharp
+using Serilog;
 
-### Enabling `Microsoft.Extensions.Logging.ILoggerProvider`s
+public class Program
+{
+    public static int Main(string[] args)
+    {
+        Log.Logger = new LoggerConfiguration()
+            .MinimumLevel.Override("Microsoft", LogEventLevel.Information)
+            .Enrich.FromLogContext()
+            .WriteTo.Console()
+            .CreateBootstrapLogger(); <-- this line!
+```
 
-Serilog sends events to outputs called _sinks_, that implement Serilog's `ILogEventSink` interface, and are added to the logging pipeline using `WriteTo`. _Microsoft.Extensions.Logging_ has a similar concept called _providers_, and these implement `ILoggerProvider`. Providers are what the default logging configuration creates under the hood through methods like `AddConsole()`.
+Then, pass a callback to `UseSerilog()` that creates the final logger:
 
-By default, Serilog ignores providers, since there are usually equivalent Serilog sinks available, and these work more efficiently with Serilog's pipeline. If provider support is needed, it can be optionally enabled.
+```csharp
+        public static IHostBuilder CreateHostBuilder(string[] args) =>
+            Host.CreateDefaultBuilder(args)
+                .UseSerilog((context, services, configuration) => configuration
+                    .ReadFrom.Configuration(context.Configuration)
+                    .ReadFrom.Services(services)
+                    .Enrich.FromLogContext()
+                    .WriteTo.Console())
+                .ConfigureWebHostDefaults(webBuilder =>
+                {
+                    webBuilder.UseStartup<Startup>();
+                });
+```
 
-**Using the recommended configuration:**
+It's important to note that the final logger **completely replaces** the bootstrap logger: if you want both to log to the console, for instance, you'll need to specify `WriteTo.Console()` in both places, as the example shows.
 
-In the recommended configuration (in which startup exceptions are caught and logged), first create a `LoggerProviderCollection` in a static field in _Program.cs_:
+#### Consuming `appsettings.json` configuration
 
-```csharp
-        // using Serilog.Extensions.Logging;
-        static readonly LoggerProviderCollection Providers = new LoggerProviderCollection();
-```
+**Using two-stage initialization**, insert the `ReadFrom.Configuration(context.Configuration)` call shown in the example above. The JSON configuration syntax is documented in [the _Serilog.Settings.Configuration_ README](https://github.com/serilog/serilog-settings-configuration)/
 
-Next, add `WriteTo.Providers()` to the logger configuration:
+#### Injecting services into enrichers and sinks
 
-```csharp
-                .WriteTo.Providers(Providers)
-```
+**Using two-stage initialization**, insert the `ReadFrom.Services(services)` call shown in the example above. The `ReadFrom.Services()` call will configure the logging pipeline with any registred implementations of the following services:
 
-Finally, pass the provider collection into `UseSerilog()`:
+ * `IDestructuringPolicy`
+ * `ILogEventEnricher`
+ * `ILogEventFilter`
+ * `ILogEventSink`
+ * `LoggingLevelSwitch`
 
-```csharp
-                   .UseSerilog(providers: Providers)
-```
+#### Enabling `Microsoft.Extensions.Logging.ILoggerProvider`s
 
-Providers registered in _Startup.cs_ with `AddLogging()` will then receive events from Serilog.
+Serilog sends events to outputs called _sinks_, that implement Serilog's `ILogEventSink` interface, and are added to the logging pipeline using `WriteTo`. _Microsoft.Extensions.Logging_ has a similar concept called _providers_, and these implement `ILoggerProvider`. Providers are what the default logging configuration creates under the hood through methods like `AddConsole()`.
 
-**Using inline initialization:**
+By default, Serilog ignores providers, since there are usually equivalent Serilog sinks available, and these work more efficiently with Serilog's pipeline. If provider support is needed, it can be optionally enabled.
 
-If [inline initialization](#inline-initialization) is used, providers can be enabled by adding `writeToProviders: true` to the `UseSerilog()` method call:
+To have Serilog pass events to providers, **using two-stage initialization** as above, pass `writeToProviders: true` in the call to `UseSerilog()`:
 
 ```csharp
     .UseSerilog(
-        (hostingContext, loggerConfiguration) => /* snip! */,
+        (hostingContext, services, loggerConfiguration) => /* snip! */,
         writeToProviders: true)
 ```
 
@@ -278,7 +291,7 @@ The Azure Diagnostic Log Stream ships events from any files in the `D:\home\LogF
 
 ### Pushing properties to the `ILogger<T>`
 
-If you want to add extra properties to all logevents in a specific part of your code, you can add them to the **`ILogger<T>`** in **Microsoft.Extensions.Logging** with the following code. For this code to work, make sure you have added the `.Enrich.FromLogContext()` to the `.UseSerilog(...)` statement, as specified in the samples above.
+If you want to add extra properties to all log events in a specific part of your code, you can add them to the **`ILogger<T>`** in **Microsoft.Extensions.Logging** with the following code. For this code to work, make sure you have added the `.Enrich.FromLogContext()` to the `.UseSerilog(...)` statement, as specified in the samples above.
 
 ```csharp
 // Microsoft.Extensions.Logging ILogger<T>

global.json

@@ -1,7 +1,7 @@
 {
   "sdk": {
     "allowPrerelease": false,
-    "version": "3.1.201",
+    "version": "5.0.102",
     "rollForward": "latestFeature"
   }
 }