Add Api Health checks

- VotingMonitor health check
- Redis health check
- Windows Azure health check
- Firebase health check

Redis, Windows Azure and Firebase are configured
to be checked only on specific conditions
that depend on their configuration settings

Runtime configuration changes are considered
so if you enable a health check while the
application is running, then this is executed
otherwise the health check is tagged as not run

Health Check endpoint /health is customized to
include specific details for each health check

The health checks are published on Application Insights

src/VotingIrregularities.sln

@@ -48,6 +48,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 		.editorconfig = .editorconfig
 	EndProjectSection
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "VoteMonitor.Api.Tests", "test\VoteMonitor.Api.Tests\VoteMonitor.Api.Tests.csproj", "{C19B6C2B-D63C-426A-ADED-00C4F5B78929}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -126,6 +128,10 @@ Global
 		{674C9094-58B8-4749-9EB1-2FFD054B8D7D}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{674C9094-58B8-4749-9EB1-2FFD054B8D7D}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{674C9094-58B8-4749-9EB1-2FFD054B8D7D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{C19B6C2B-D63C-426A-ADED-00C4F5B78929}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C19B6C2B-D63C-426A-ADED-00C4F5B78929}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C19B6C2B-D63C-426A-ADED-00C4F5B78929}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C19B6C2B-D63C-426A-ADED-00C4F5B78929}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -149,6 +155,7 @@ Global
 		{DD341123-8FD7-4506-AA0D-4280A5112A6F} = {8A09B442-FB79-4293-BF9B-E34DD3AE70F3}
 		{C7767496-1BC5-41AD-98D1-439BAA2ACEAE} = {388C55EB-26FF-46AB-9395-549E1A7A99AD}
 		{674C9094-58B8-4749-9EB1-2FFD054B8D7D} = {8A09B442-FB79-4293-BF9B-E34DD3AE70F3}
+		{C19B6C2B-D63C-426A-ADED-00C4F5B78929} = {388C55EB-26FF-46AB-9395-549E1A7A99AD}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {AF1523BC-7F31-4564-8E1B-D2DB4552FFCB}

src/api/VoteMonitor.Api.Core/Services/CacheService.cs

@@ -12,7 +12,7 @@ public class CacheService : ICacheService
         private readonly IDistributedCache _cache;
         private readonly ILogger _logger;
 
-        public CacheService(IDistributedCache cache, ILogger logger)
+        public CacheService(IDistributedCache cache, ILogger<CacheService> logger)
         {
             _cache = cache;
             _logger = logger;

src/api/VoteMonitor.Api/Extensions/HealthChecks/AzureBlobStorageHealthChecksExtensions.cs

@@ -0,0 +1,54 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Options;
+using Microsoft.WindowsAzure.Storage;
+using Microsoft.WindowsAzure.Storage.Auth;
+using Microsoft.WindowsAzure.Storage.Blob;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using VoteMonitor.Api.Core.Options;
+
+namespace VoteMonitor.Api.Extensions.HealthChecks
+{
+    public static class AzureBlobStorageHealthChecksExtensions
+    {
+        public static IHealthChecksBuilder AddAzureBlobStorage(this IHealthChecksBuilder builder, string name)
+            => builder.Add(new HealthCheckRegistration(
+                   name,
+                   sp => new AzureBlobStorageHealthCheck(sp.GetService<IOptionsSnapshot<BlobStorageOptions>>()), null, null, null));
+    }
+
+    public class AzureBlobStorageHealthCheck : IHealthCheck
+    {
+        private IOptions<BlobStorageOptions> _storageOptions;
+
+        public AzureBlobStorageHealthCheck(IOptions<BlobStorageOptions> storageOptions)
+        {
+            _storageOptions = storageOptions;
+        }
+
+        public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
+        {
+            try
+            {
+                var credentials = new StorageCredentials(_storageOptions.Value.AccountName, _storageOptions.Value.AccountKey);
+                var blobClient = new CloudStorageAccount(credentials, _storageOptions.Value.UseHttps).CreateCloudBlobClient();
+
+                var serviceProperties = await blobClient.GetServicePropertiesAsync(
+                    new BlobRequestOptions(),
+                    operationContext: null,
+                    cancellationToken: cancellationToken);
+
+                var container = blobClient.GetContainerReference(_storageOptions.Value.Container);
+                await container.FetchAttributesAsync();
+
+                return HealthCheckResult.Healthy();
+            }
+            catch (Exception ex)
+            {
+                return new HealthCheckResult(context.Registration.FailureStatus, exception: ex);
+            }
+        }
+    }
+}

src/api/VoteMonitor.Api/Extensions/HealthChecks/ConditionalHealthCheck.cs

@@ -0,0 +1,71 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Logging;
+using System;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace VoteMonitor.Api.Extensions.HealthChecks
+{
+    public static class ConditionalHealthChecksExtensions
+    {
+        public static IHealthChecksBuilder CheckOnlyWhen(this IHealthChecksBuilder builder, string name, Func<bool> predicate)
+        {
+            builder.Services.Configure<HealthCheckServiceOptions>(options =>
+            {
+                var registration = options.Registrations.FirstOrDefault(c => c.Name == name);
+
+                if (registration == null)
+                {
+                    throw new InvalidOperationException($"A health check registration named `{name}` is not found in the health registrations list, so its conditional check cannot be configured. The registration must be added before configuring the conditional predicate.");
+                }
+
+                var factory = registration.Factory;
+                registration.Factory = sp => new ConditionalHealthCheck(
+                       () => factory(sp),
+                       predicate,
+                       sp.GetService<ILogger<ConditionalHealthCheck>>()
+                   );
+            });
+
+            return builder;
+        }
+    }
+
+    public class ConditionalHealthCheck : IHealthCheck
+    {
+        private const string NotChecked = "NotChecked";
+        private readonly Func<bool> _predicate;
+        private readonly ILogger<ConditionalHealthCheck> _logger;
+
+        public ConditionalHealthCheck(Func<IHealthCheck> healthCheckFactory,
+            Func<bool> predicate,
+            ILogger<ConditionalHealthCheck> logger)
+        {
+            HealthCheckFactory = healthCheckFactory;
+            _predicate = predicate;
+            _logger = logger;
+        }
+
+        public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
+        {
+            context.Registration.Tags.Remove(NotChecked);
+
+            if (!_predicate())
+            {
+                _logger.LogDebug("Healthcheck `{0}` will not be executed as its checking condition is not met.", context.Registration.Name);
+
+                context.Registration.Tags.Add(NotChecked);
+
+                return new HealthCheckResult(HealthStatus.Healthy, $"Health check on `{context.Registration.Name}` will not be evaluated " +
+                    $"as its checking condition is not met. This does not mean your dependency is healthy, " +
+                    $"but the health check operation on this dependency is not configured to be executed yet.");
+            }
+
+            return await HealthCheckFactory().CheckHealthAsync(context, cancellationToken);
+        }
+
+        internal Func<IHealthCheck> HealthCheckFactory { get; set; }
+    }
+}

src/api/VoteMonitor.Api/Extensions/HealthChecks/FirebaseHealthChecksExtensions.cs

@@ -0,0 +1,44 @@
+using FirebaseAdmin;
+using FirebaseAdmin.Auth;
+using Google.Apis.Auth.OAuth2;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace VoteMonitor.Api.Extensions.HealthChecks
+{
+    public static class FirebaseHealthChecksExtensions
+    {
+        public static IHealthChecksBuilder AddFirebase(this IHealthChecksBuilder builder, string name)
+            => builder.Add(new HealthCheckRegistration(
+                   name,
+                   sp => new FirebaseHealthCheck(), null, null, null));
+    }
+
+    public class FirebaseHealthCheck : IHealthCheck
+    {
+        public Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default)
+        {
+            try
+            {
+                if (FirebaseApp.DefaultInstance == null)
+                {
+                    FirebaseApp.Create(new AppOptions()
+                    {
+                        Credential = GoogleCredential.GetApplicationDefault(),
+                    });
+                }
+
+                var defaultAuth = FirebaseAuth.DefaultInstance;
+
+                return Task.FromResult(HealthCheckResult.Healthy());
+            }
+            catch (Exception ex)
+            {
+                return Task.FromResult(new HealthCheckResult(context.Registration.FailureStatus, exception: ex));
+            }
+        }
+    }
+}

src/api/VoteMonitor.Api/Extensions/HealthChecksConfiguration.cs

@@ -0,0 +1,66 @@
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Hosting;
+using System;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.Json;
+using System.Threading.Tasks;
+
+namespace VoteMonitor.Api.Extensions
+{
+    public static class HealthChecksConfiguration
+    {
+        public static async Task WriteResponse(HttpContext context, HealthReport result, IWebHostEnvironment env)
+        {
+            context.Response.ContentType = "application/json; charset=utf-8";
+
+            var options = new JsonSerializerOptions
+            {               
+                IgnoreNullValues = true
+            };
+
+            using var stream = new MemoryStream();
+
+            var healthResponse = new
+            {
+                status = result.Status.ToString(),
+                totalDuration = result.TotalDuration.ToString(),
+                entries = result.Entries.Select(e => new
+                {
+                    name = e.Key,
+                    status = e.Value.Status.ToString(),
+                    tags = e.Value.Tags,
+                    description = e.Value.Description,
+                    data = env.IsDevelopment() && e.Value.Data?.Count > 0 ? e.Value.Data : null,
+                    exception = env.IsDevelopment() ? ExtractSerializableExceptionData(e.Value.Exception) : null
+                }).ToList()
+            };
+
+            await JsonSerializer.SerializeAsync(stream, healthResponse, healthResponse.GetType(), options);
+            var json = Encoding.UTF8.GetString(stream.ToArray());
+
+            await context.Response.WriteAsync(json);
+
+            static object ExtractSerializableExceptionData(Exception exception)
+            {
+                if (exception == null)
+                {
+                    return exception;
+                }
+
+                return new
+                {
+                    type = exception.GetType().ToString(),
+                    message = exception.Message,
+                    stackTrace = exception.StackTrace,
+                    source = exception.Source,
+                    data = exception.Data?.Count > 0 ? exception.Data : null,
+                    innerException = exception.InnerException != null ? ExtractSerializableExceptionData(exception.InnerException) : null
+                };
+            };
+        }
+    }
+}

src/api/VoteMonitor.Api/Extensions/ServicesExtensions.cs

@@ -5,6 +5,8 @@
 using VoteMonitor.Api.Core.Extensions;
 using VoteMonitor.Api.Core.Options;
 using VoteMonitor.Api.Core.Services;
+using VoteMonitor.Api.Extensions.HealthChecks;
+using VoteMonitor.Entities;
 
 namespace VoteMonitor.Api.Extensions
 {
@@ -89,5 +91,19 @@ public static IServiceCollection AddFirebase(this IServiceCollection services,
 
             return services;
         }
+
+        public static IServiceCollection AddHealthChecks(this IServiceCollection services, IConfiguration configuration)
+        {
+            services.AddHealthChecks()
+                .AddDbContextCheck<VoteMonitorContext>()
+                .AddRedis(configuration["RedisCacheOptions:Configuration"], "Redis")
+                    .CheckOnlyWhen("Redis", () => configuration["ApplicationCacheOptions:Implementation"] == "RedisCache")
+                .AddAzureBlobStorage("AzureBlobStorage")
+                    .CheckOnlyWhen("AzureBlobStorage", () => !(configuration["FileServiceOptions:Type"] == "LocalFileService"))
+                .AddFirebase("Firebase")
+                    .CheckOnlyWhen("Firebase", () => !string.IsNullOrEmpty(configuration["FirebaseServiceOptions:ServerKey"]))
+                .AddApplicationInsightsPublisher();
+            return services;
+        }
     }
 }

src/api/VoteMonitor.Api/Properties/launchSettings.json

@@ -20,7 +20,16 @@
     "VoteMonitor.Api": {
       "commandName": "Project",
       "launchBrowser": true,
-      "launchUrl": "weatherforecast",
+      "launchUrl": "swagger",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      },
+      "applicationUrl": "https://localhost:5001;http://localhost:5000"
+    },
+    "VoteMonitor.Api HealthChecks": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "launchUrl": "health",
       "environmentVariables": {
         "ASPNETCORE_ENVIRONMENT": "Development"
       },

src/api/VoteMonitor.Api/Startup.cs

@@ -1,21 +1,24 @@
 using AutoMapper;
 using MediatR;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Diagnostics.HealthChecks;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
-using Microsoft.Extensions.Logging;
+using System.Runtime.CompilerServices;
 using VoteMonitor.Api.Core.Extensions;
 using VoteMonitor.Api.Extensions;
+using VoteMonitor.Api.Form;
 using VoteMonitor.Api.Location.Services;
 using VoteMonitor.Entities;
-using VoteMonitor.Api.Form;
 
+[assembly: InternalsVisibleTo("VoteMonitor.Api.Tests")]
 namespace VoteMonitor.Api
 {
     public class Startup
@@ -49,6 +52,7 @@ public void ConfigureServices(IServiceCollection services)
             services.ConfigureSwagger();
             services.AddApplicationInsightsTelemetry();
             services.AddCachingService(Configuration);
+            services.AddHealthChecks(Configuration);
         }
 
         // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
@@ -69,6 +73,10 @@ public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<
 
             app.UseEndpoints(endpoints =>
             {
+                endpoints.MapHealthChecks("/health", new HealthCheckOptions
+                {
+                    ResponseWriter = async (context, result) => await HealthChecksConfiguration.WriteResponse(context, result, env)
+                });
                 endpoints.MapControllers();
             });
         }
@@ -84,7 +92,7 @@ private IEnumerable<Assembly> GetAssemblies()
             yield return typeof(Form.Controllers.FormController).GetTypeInfo().Assembly;
             yield return typeof(Location.Controllers.PollingStationController).GetTypeInfo().Assembly;
             yield return typeof(Note.Controllers.NoteController).GetTypeInfo().Assembly;
-            yield return typeof(Notification.Controllers.NotificationController).GetTypeInfo().Assembly;            
+            yield return typeof(Notification.Controllers.NotificationController).GetTypeInfo().Assembly;
             yield return typeof(Observer.Controllers.ObserverController).GetTypeInfo().Assembly;
             yield return typeof(Statistics.Controllers.StatisticsController).GetTypeInfo().Assembly;
             yield return typeof(PollingStation.Controllers.PollingStationController).GetTypeInfo().Assembly;