Support health check

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

@@ -0,0 +1,41 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using System;
+using System.Threading.Tasks;
+using System.Threading;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
+{
+    internal class AzureAppConfigurationHealthCheck : IConfigurationHealthCheck
+    {
+        private AzureAppConfigurationProvider _provider = null;
+
+        internal void SetProvider(AzureAppConfigurationProvider provider)
+        {
+            _provider = provider ?? throw new ArgumentNullException(nameof(provider));
+        }
+
+        public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
+        {
+            if (_provider == null)
+            {
+                return HealthCheckResult.Unhealthy("Configuration provider is not set.");
+            }
+
+            if (!_provider.LastSuccessfulAttempt.HasValue)
+            {
+                return HealthCheckResult.Unhealthy("The initial load is not completed.");
+            }
+
+            if (_provider.LastFailedAttempt.HasValue &&
+                _provider.LastSuccessfulAttempt.Value < _provider.LastFailedAttempt.Value)
+            {
+                return HealthCheckResult.Unhealthy("The last refresh attempt failed.");
+            }
+
+            return HealthCheckResult.Healthy();
+        }
+    }
+}

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

@@ -2,7 +2,7 @@
 // Licensed under the MIT license.
 //
 using Azure.Core;
-using Azure.Core.Pipeline;
+using Azure.Core.Pipeline;
 using Azure.Data.AppConfiguration;
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.AzureKeyVault;
 using Microsoft.Extensions.Configuration.AzureAppConfiguration.Extensions;
@@ -11,7 +11,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Net.Http;
+using System.Net.Http;
 using System.Threading.Tasks;
 
 namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
@@ -25,14 +25,15 @@ public class AzureAppConfigurationOptions
         private const int MaxRetries = 2;
         private static readonly TimeSpan MaxRetryDelay = TimeSpan.FromMinutes(1);
         private static readonly TimeSpan NetworkTimeout = TimeSpan.FromSeconds(10);
-        private static readonly KeyValueSelector DefaultQuery = new KeyValueSelector { KeyFilter = KeyFilter.Any, LabelFilter = LabelFilter.Null };
+        private static readonly KeyValueSelector DefaultQuery = new KeyValueSelector { KeyFilter = KeyFilter.Any, LabelFilter = LabelFilter.Null };
 
         private List<KeyValueWatcher> _individualKvWatchers = new List<KeyValueWatcher>();
         private List<KeyValueWatcher> _ffWatchers = new List<KeyValueWatcher>();
         private List<IKeyValueAdapter> _adapters;
         private List<Func<ConfigurationSetting, ValueTask<ConfigurationSetting>>> _mappers = new List<Func<ConfigurationSetting, ValueTask<ConfigurationSetting>>>();
         private List<KeyValueSelector> _selectors;
         private IConfigurationRefresher _refresher = new AzureAppConfigurationRefresher();
+        private IConfigurationHealthCheck _healthCheck = new AzureAppConfigurationHealthCheck();
         private bool _selectCalled = false;
 
         // The following set is sorted in descending order.
@@ -459,6 +460,15 @@ public IConfigurationRefresher GetRefresher()
             return _refresher;
         }
 
+        /// <summary>
+        /// Get an instance of <see cref="IConfigurationHealthCheck"/> that can be used to do health checks for the configuration provider.
+        /// </summary>
+        /// <returns>An instance of <see cref="IConfigurationHealthCheck"/>.</returns>
+        public IConfigurationHealthCheck GetHealthCheck()
+        {
+            return _healthCheck;
+        }
+
         /// <summary>
         /// Configures the Azure App Configuration provider to use the provided Key Vault configuration to resolve key vault references.
         /// </summary>
@@ -514,9 +524,9 @@ private static ConfigurationClientOptions GetDefaultClientOptions()
             clientOptions.Retry.Mode = RetryMode.Exponential;
             clientOptions.AddPolicy(new UserAgentHeaderPolicy(), HttpPipelinePosition.PerCall);
             clientOptions.Transport = new HttpClientTransport(new HttpClient()
-            {
+            {
                 Timeout = NetworkTimeout
-            });
+            });
 
             return clientOptions;
         }

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

@@ -58,6 +58,9 @@ private class ConfigurationClientBackoffStatus
             public DateTimeOffset BackoffEndTime { get; set; }
         }
 
+        public DateTimeOffset? LastSuccessfulAttempt { get; private set; } = null;
+        public DateTimeOffset? LastFailedAttempt { get; private set; } = null;
+
         public Uri AppConfigurationEndpoint
         {
             get
@@ -116,6 +119,9 @@ public AzureAppConfigurationProvider(IConfigurationClientManager configClientMan
             bool hasWatchers = watchers.Any();
             TimeSpan minWatcherRefreshInterval = hasWatchers ? watchers.Min(w => w.RefreshInterval) : TimeSpan.MaxValue;
 
+            var healthCheck = (AzureAppConfigurationHealthCheck)_options.GetHealthCheck();
+            healthCheck.SetProvider(this);
+
             if (options.RegisterAllEnabled)
             {
                 if (options.KvCollectionRefreshInterval <= TimeSpan.Zero)
@@ -255,6 +261,8 @@ public async Task RefreshAsync(CancellationToken cancellationToken)
 
                         _logger.LogDebug(LogHelper.BuildRefreshSkippedNoClientAvailableMessage());
 
+                        LastFailedAttempt = DateTime.UtcNow;
+
                         return;
                     }
 
@@ -1135,6 +1143,7 @@ private async Task<T> ExecuteWithFailOverPolicyAsync<T>(
                     success = true;
 
                     _lastSuccessfulEndpoint = _configClientManager.GetEndpointForClient(currentClient);
+                    LastSuccessfulAttempt = DateTime.UtcNow;
 
                     return result;
                 }
@@ -1143,6 +1152,7 @@ private async Task<T> ExecuteWithFailOverPolicyAsync<T>(
                     if (!IsFailOverable(rfe) || !clientEnumerator.MoveNext())
                     {
                         backoffAllClients = true;
+                        LastFailedAttempt = DateTime.UtcNow;
 
                         throw;
                     }
@@ -1152,6 +1162,7 @@ private async Task<T> ExecuteWithFailOverPolicyAsync<T>(
                     if (!IsFailOverable(ae) || !clientEnumerator.MoveNext())
                     {
                         backoffAllClients = true;
+                        LastFailedAttempt = DateTime.UtcNow;
 
                         throw;
                     }

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

@@ -0,0 +1,14 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+
+namespace Microsoft.Extensions.Configuration.AzureAppConfiguration
+{
+    /// <summary>
+    /// An interface for Azure App Configuration health check.
+    /// </summary>
+    public interface IConfigurationHealthCheck : IHealthCheck
+    {
+    }
+}

src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Microsoft.Extensions.Configuration.AzureAppConfiguration.csproj

@@ -19,6 +19,7 @@
     <PackageReference Include="Azure.Messaging.EventGrid" Version="4.7.0" />
     <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.6.0" />
     <PackageReference Include="DnsClient" Version="1.7.0" />
+    <PackageReference Include="Microsoft.Extensions.Diagnostics.HealthChecks" Version="6.0.36" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="6.0.0" />
     <PackageReference Include="Microsoft.Extensions.Logging" Version="6.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="6.0.1" />

tests/Tests.AzureAppConfiguration/HealthCheckTest.cs

@@ -0,0 +1,110 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+//
+using Azure;
+using Azure.Data.AppConfiguration;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Configuration.AzureAppConfiguration;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Moq;
+using System.Threading;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Xunit;
+using System;
+using System.Linq;
+
+namespace Tests.AzureAppConfiguration
+{
+    public class HealthCheckTest
+    {
+        readonly List<ConfigurationSetting> kvCollection = new List<ConfigurationSetting>
+        {
+            ConfigurationModelFactory.ConfigurationSetting("TestKey1", "TestValue1", "label",
+                eTag: new ETag("0a76e3d7-7ec1-4e37-883c-9ea6d0d89e63"),
+                contentType:"text"),
+            ConfigurationModelFactory.ConfigurationSetting("TestKey2", "TestValue2", "label",
+                eTag: new ETag("31c38369-831f-4bf1-b9ad-79db56c8b989"),
+                contentType: "text"),
+            ConfigurationModelFactory.ConfigurationSetting("TestKey3", "TestValue3", "label",
+
+                eTag: new ETag("bb203f2b-c113-44fc-995d-b933c2143339"),
+                contentType: "text"),
+            ConfigurationModelFactory.ConfigurationSetting("TestKey4", "TestValue4", "label",
+                eTag: new ETag("3ca43b3e-d544-4b0c-b3a2-e7a7284217a2"),
+                contentType: "text"),
+        };
+
+        [Fact]
+        public async Task HealthCheckTests_ReturnsHealthyWhenInitialLoadIsCompleted()
+        {
+            IHealthCheck healthCheck = null;
+
+            var mockResponse = new Mock<Response>();
+            var mockClient = new Mock<ConfigurationClient>(MockBehavior.Strict);
+
+            mockClient.Setup(c => c.GetConfigurationSettingsAsync(It.IsAny<SettingSelector>(), It.IsAny<CancellationToken>()))
+                .Returns(new MockAsyncPageable(kvCollection));
+
+            var config = new ConfigurationBuilder()
+                .AddAzureAppConfiguration(options =>
+                {
+                    options.ClientManager = TestHelpers.CreateMockedConfigurationClientManager(mockClient.Object);
+                    healthCheck = options.GetHealthCheck();
+                })
+                .Build();
+
+            Assert.True(config["TestKey1"] == "TestValue1");
+            var result = await healthCheck.CheckHealthAsync(new HealthCheckContext());
+            Assert.Equal(HealthStatus.Healthy, result.Status);
+        }
+
+        [Fact]
+        public async Task HealthCheckTests_ReturnsUnhealthyWhenRefreshFailed()
+        {
+            IConfigurationRefresher refresher = null;
+            IHealthCheck healthCheck = null;
+            var mockResponse = new Mock<Response>();
+            var mockClient = new Mock<ConfigurationClient>(MockBehavior.Strict);
+
+            mockClient.SetupSequence(c => c.GetConfigurationSettingsAsync(It.IsAny<SettingSelector>(), It.IsAny<CancellationToken>()))
+                       .Returns(new MockAsyncPageable(kvCollection))
+                       .Throws(new RequestFailedException(503, "Request failed."))
+                       .Returns(new MockAsyncPageable(Enumerable.Empty<ConfigurationSetting>().ToList()))
+                       .Returns(new MockAsyncPageable(Enumerable.Empty<ConfigurationSetting>().ToList()));
+
+            var config = new ConfigurationBuilder()
+                .AddAzureAppConfiguration(options =>
+                {
+                    options.ClientManager = TestHelpers.CreateMockedConfigurationClientManager(mockClient.Object);
+                    options.MinBackoffDuration = TimeSpan.FromSeconds(2);
+                    options.ConfigurationSettingPageIterator = new MockConfigurationSettingPageIterator();
+                    options.ConfigureRefresh(refreshOptions =>
+                    {
+                        refreshOptions.RegisterAll()
+                            .SetRefreshInterval(TimeSpan.FromSeconds(1));
+                    });
+                    refresher = options.GetRefresher();
+                    healthCheck = options.GetHealthCheck();
+                })
+                .Build();
+
+            var result = await healthCheck.CheckHealthAsync(new HealthCheckContext());
+            Assert.Equal(HealthStatus.Healthy, result.Status);
+
+            // Wait for the refresh interval to expire
+            Thread.Sleep(1000);
+
+            await refresher.TryRefreshAsync();
+            result = await healthCheck.CheckHealthAsync(new HealthCheckContext());
+            Assert.Equal(HealthStatus.Unhealthy, result.Status);
+
+            // Wait for client backoff to end
+            Thread.Sleep(3000);
+
+            await refresher.RefreshAsync();
+            result = await healthCheck.CheckHealthAsync(new HealthCheckContext());
+            Assert.Equal(HealthStatus.Healthy, result.Status);
+        }
+    }
+}

tests/Tests.AzureAppConfiguration/RefreshTests.cs

@@ -320,7 +320,7 @@ Response<ConfigurationSetting> GetIfChanged(ConfigurationSetting setting, bool o
                     foreach (var setting in keyValueCollection)
                     {
                         copy.Add(TestHelpers.CloneSetting(setting));
-                    };
+                    }
 
                     return new MockAsyncPageable(copy);
                 });
@@ -392,7 +392,7 @@ Response<ConfigurationSetting> GetIfChanged(ConfigurationSetting setting, bool o
                     foreach (var setting in keyValueCollection)
                     {
                         copy.Add(TestHelpers.CloneSetting(setting));
-                    };
+                    }
 
                     return new MockAsyncPageable(copy);
                 });
@@ -461,7 +461,7 @@ public async Task RefreshTests_SingleServerCallOnSimultaneousMultipleRefresh()
                     foreach (var setting in keyValueCollection)
                     {
                         copy.Add(TestHelpers.CloneSetting(setting));
-                    };
+                    }
 
                     return new MockAsyncPageable(copy, operationDelay);
                 });