Add fail-over support to config provider.

Microsoft.Extensions.Configuration.AzureAppConfiguration.sln

@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 16
-VisualStudioVersion = 16.0.29920.165
+# Visual Studio Version 17
+VisualStudioVersion = 17.3.32503.460
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Configuration.AzureAppConfiguration", "src\Microsoft.Extensions.Configuration.AzureAppConfiguration\Microsoft.Extensions.Configuration.AzureAppConfiguration.csproj", "{7B793D44-EC46-4C12-B71F-3A5005290C75}"
 EndProject
@@ -19,6 +19,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Azure.AppConfigur
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Tests.AzureAppConfiguration.Functions.Worker", "tests\Tests.AzureAppConfiguration.Functions.Worker\Tests.AzureAppConfiguration.Functions.Worker.csproj", "{A9287214-6689-479F-A9F8-D0C02DE433F0}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ConsoleAppWithFailOver", "examples\ConsoleAppWithFailOver\ConsoleAppWithFailOver.csproj", "{A6C611F1-D687-4262-8904-828C239CF2E5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -57,6 +59,10 @@ Global
 		{A9287214-6689-479F-A9F8-D0C02DE433F0}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A9287214-6689-479F-A9F8-D0C02DE433F0}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A9287214-6689-479F-A9F8-D0C02DE433F0}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A6C611F1-D687-4262-8904-828C239CF2E5}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A6C611F1-D687-4262-8904-828C239CF2E5}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A6C611F1-D687-4262-8904-828C239CF2E5}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A6C611F1-D687-4262-8904-828C239CF2E5}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

examples/ConsoleAppWithFailOver/ConsoleAppWithFailOver.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Azure.Identity" Version="1.5.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="5.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.Extensions.Configuration.AzureAppConfiguration\Microsoft.Extensions.Configuration.AzureAppConfiguration.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>

examples/ConsoleAppWithFailOver/Program.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+
+using Azure.Identity;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration.Examples.ConsoleApplicationWithFailOver
+{
+    class Program
+    {
+        static IConfiguration Configuration { get; set; }
+
+        static void Main(string[] args)
+        {
+            Configure();
+
+            Console.WriteLine($"The AppName is: {Configuration?["AppName"]}.");
+        }
+
+        private static void Configure()
+        {
+            var builder = new ConfigurationBuilder();
+
+            // Load a subset of the application's configuration from a json file and environment variables
+            builder.AddJsonFile("appsettings.json")
+                   .AddEnvironmentVariables();
+
+            IConfiguration configuration = builder.Build();
+
+            IConfigurationSection endpointsSection = configuration.GetSection("AppConfig:Endpoints");
+            IEnumerable<Uri> endpoints = endpointsSection.GetChildren().Select(endpoint => new Uri(endpoint.Value));
+
+            if (endpoints == null || !endpoints.Any())
+            {
+                Console.WriteLine("Endpoints not found.");
+                Console.WriteLine("Please set the array 'Appconfig:Endpoints' in appsettings.json with valid Azure App Configuration replica endpoints and re-run this example.");
+                return;
+            }
+
+            // Augment the configuration builder with Azure App Configuration
+            builder.AddAzureAppConfiguration(options =>
+            {
+                options.Connect(endpoints, new DefaultAzureCredential());
+            });
+
+            Configuration = builder.Build();
+        }
+    }
+}

examples/ConsoleAppWithFailOver/appsettings.json

@@ -0,0 +1,6 @@
+{
+  "AppName": "Azure App Configuration Console App with FailOver support",
+  "AppConfig": {
+    "Endpoints": [ ]
+  }
+}

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationExtensions.cs

@@ -58,13 +58,5 @@ public static IServiceCollection AddAzureAppConfiguration(this IServiceCollectio
             services.AddSingleton<IConfigurationRefresherProvider, AzureAppConfigurationRefresherProvider>();
             return services;
         }
-
-        internal static IConfigurationBuilder AddAzureAppConfiguration(
-            this IConfigurationBuilder configurationBuilder,
-            Action<AzureAppConfigurationOptions> action,
-            IConfigurationClientFactory configurationClientFactory)
-        {
-            return configurationBuilder.Add(new AzureAppConfigurationSource(action, optional: false, configurationClientFactory));
-        }
     }
 }

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationOptions.cs

@@ -42,14 +42,14 @@ public class AzureAppConfigurationOptions
         internal string ConnectionString { get; private set; }
 
         /// <summary>
-        /// The endpoint of the Azure App Configuration.
+        /// The list of endpoints of an Azure App Configuration store.
         /// If this property is set, the <see cref="Credential"/> property also needs to be set.
         /// </summary>
-        internal Uri Endpoint { get; private set; }
+        internal IEnumerable<Uri> Endpoints { get; private set; }
 
         /// <summary>
-        /// The connection string to use to connect to Azure App Configuration.
-        /// If this property is set, the <see cref="Endpoint"/> property also needs to be set.
+        /// The credential used to connect to the Azure App Configuration.
+        /// If this property is set, the <see cref="Endpoints"/> property also needs to be set.
         /// </summary>
         internal TokenCredential Credential { get; private set; }
 
@@ -83,9 +83,10 @@ internal IEnumerable<IKeyValueAdapter> Adapters
         internal IEnumerable<string> KeyPrefixes => _keyPrefixes;
 
         /// <summary>
-        /// An optional client that can be used to communicate with Azure App Configuration. If provided, the connection string property will be ignored.
+        /// An optional configuration client manager that can be used to provide clients to communicate with Azure App Configuration.
         /// </summary>
-        internal ConfigurationClient Client { get; set; }
+        /// <remarks>This property is used only for unit testing.</remarks>
+        internal IConfigurationClientManager ClientManager { get; set; }
 
         /// <summary>
         /// Options used to configure the client used to communicate with Azure App Configuration.
@@ -256,7 +257,7 @@ public AzureAppConfigurationOptions Connect(string connectionString)
                 throw new ArgumentNullException(nameof(connectionString));
             }
 
-            Endpoint = null;
+            Endpoints = null;
             Credential = null;
             ConnectionString = connectionString;
             return this;
@@ -279,9 +280,30 @@ public AzureAppConfigurationOptions Connect(Uri endpoint, TokenCredential creden
                 throw new ArgumentNullException(nameof(credential));
             }
 
+            return Connect(new List<Uri>() { endpoint }, credential);
+        }
+
+        /// <summary>
+        /// Connect the provider to an Azure App Configuration store and its replicas using a list of endpoints and a token credential.
+        /// </summary>
+        /// <param name="endpoints">The list of endpoints of an Azure App Configuration store and its replicas to connect to.</param>
+        /// <param name="credential">Token credential to use to connect.</param>
+        public AzureAppConfigurationOptions Connect(IEnumerable<Uri> endpoints, TokenCredential credential)
+        {
+            if (endpoints == null || !endpoints.Any())
+            {
+                throw new ArgumentNullException(nameof(endpoints));
+            }
+
+            if (endpoints.Distinct(new EndpointComparer()).Count() != endpoints.Count())
+            {
+                throw new ArgumentException($"All values in '{nameof(endpoints)}' must be unique.");
+            }
+
+            Credential = credential ?? throw new ArgumentNullException(nameof(credential));
+
+            Endpoints = endpoints;
             ConnectionString = null;
-            Endpoint = endpoint;
-            Credential = credential;
             return this;
         }