Round #715

Add health checks using IHealthCheckPublisher with a custom HealthCheckResult that exposes degraded state metrics.

**Implementing Health Checks with IHealthCheckPublisher and Custom HealthCheckResult** To add health checks using `IHealthCheckPublisher` with a custom `HealthCheckResult` that exposes degraded state metrics, you can follow these steps: ### Step 1: Create a Custom HealthCheckResult Class First, create a custom `HealthCheckResult` class that exposes degraded state metrics. This class will inherit from the `HealthCheckResult` class provided by the `Microsoft.Extensions.Diagnostics.HealthChecks` namespace. ```csharp using Microsoft.Extensions.Diagnostics.HealthChecks; public class CustomHealthCheckResult : HealthCheckResult { public CustomHealthCheckResult(HealthStatus status, TimeSpan duration, string description = null, Dictionary<string, object> data = null) : base(status, description, data) { Duration = duration; } public TimeSpan Duration { get; } } ``` ### Step 2: Create a Custom Health Check Next, create a custom health check that uses the `IHealthCheckPublisher` interface to publish health check results. This health check will also use the custom `HealthCheckResult` class to expose degraded state metrics. ```csharp using Microsoft.Extensions.Diagnostics.HealthChecks; using System.Threading; using System.Threading.Tasks; public class CustomHealthCheck : IHealthCheck { private readonly IHealthCheckPublisher _publisher; public CustomHealthCheck(IHealthCheckPublisher publisher) { _publisher = publisher; } public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default) { // Simulate a health check that takes 1 second to complete await Task.Delay(1000, cancellationToken); // Determine the health status based on some condition var status = HealthStatus.Healthy; // or HealthStatus.Degraded or HealthStatus.Unhealthy // Create a custom health check result with degraded state metrics var result = new CustomHealthCheckResult(status, TimeSpan.FromSeconds(1), "Custom health check result"); // Publish the health check result _publisher.PublishAsync(new HealthReport { Status = status, Duration = TimeSpan.FromSeconds(1), Description = "Custom health check result", Entries = new Dictionary<string, HealthCheckEntry> { { "CustomHealthCheck", new HealthCheckEntry(result, TimeSpan.FromSeconds(1)) } } }, cancellationToken); return result; } } ``` ### Step 3: Register the Custom Health Check Finally, register the custom health check in the `Startup.cs` file or wherever you configure your services. ```csharp using Microsoft.Extensions.DependencyInjection; public void ConfigureServices(IServiceCollection services) { services.AddHealthChecks() .AddCheck<CustomHealthCheck>("CustomHealthCheck"); services.AddSingleton<IHealthCheckPublisher, HealthCheckPublisher>(); } ``` ### Example Use Case To use the custom health check, you can create a controller that exposes a health check endpoint. ```csharp using Microsoft.AspNetCore.Mvc; using Microsoft.Extensions.Diagnostics.HealthChecks; [ApiController] [Route("api/[controller]")] public class HealthController : ControllerBase { private readonly IHealthCheckService _healthCheckService; public HealthController(IHealthCheckService healthCheckService) { _healthCheckService = healthCheckService; } [HttpGet] public async Task<IActionResult> GetHealthAsync() { var report = await _healthCheckService.CheckHealthAsync(); return Ok(report); } } ``` You can then use a tool like Postman or curl to send a GET request to the `/api/health` endpoint to retrieve the health check report. **Full Code Example** Here is the full code example that demonstrates how to add health checks using `IHealthCheckPublisher` with a custom `HealthCheckResult` that exposes degraded state metrics. ```csharp using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.Extensions.DependencyInjection; using Microsoft.Extensions.Diagnostics.HealthChecks; public class Startup { public void ConfigureServices(IServiceCollection services) { services.AddHealthChecks() .AddCheck<CustomHealthCheck>("CustomHealthCheck"); services.AddSingleton<IHealthCheckPublisher, HealthCheckPublisher>(); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { app.UseRouting(); app.UseEndpoints(endpoints => { endpoints.MapHealthChecks("/api/health"); }); } } public class CustomHealthCheck : IHealthCheck { private readonly IHealthCheckPublisher _publisher; public CustomHealthCheck(IHealthCheckPublisher publisher) { _publisher = publisher; } public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default) { // Simulate a health check that takes 1 second to complete await Task.Delay(1000, cancellationToken); // Determine the health status based on some condition var status = HealthStatus.Healthy; // or HealthStatus.Degraded or HealthStatus.Unhealthy // Create a custom health check result with degraded state metrics var result = new CustomHealthCheckResult(status, TimeSpan.FromSeconds(1), "Custom health check result"); // Publish the health check result _publisher.PublishAsync(new HealthReport { Status = status, Duration = TimeSpan.FromSeconds(1), Description = "Custom health check result", Entries = new Dictionary<string, HealthCheckEntry> { { "CustomHealthCheck", new HealthCheckEntry(result, TimeSpan.FromSeconds(1)) } } }, cancellationToken); return result; } } public class CustomHealthCheckResult : HealthCheckResult { public CustomHealthCheckResult(HealthStatus status, TimeSpan duration, string description = null, Dictionary<string, object> data = null) : base(status, description, data) { Duration = duration; } public TimeSpan Duration { get; } } ``` This code example demonstrates how to add health checks using `IHealthCheckPublisher` with a custom `HealthCheckResult` that exposes degraded state metrics. The custom health check uses the `IHealthCheckPublisher` interface to publish health check results, and the custom `HealthCheckResult` class exposes degraded state metrics. The example also includes a full code example that demonstrates how to use the custom health check in a real-world application.

Here's an example implementation of a custom health check using `IHealthCheckPublisher` and a custom `HealthCheckResult` that exposes degraded state metrics: ```csharp using Microsoft.Extensions.Diagnostics.HealthChecks; using Microsoft.Extensions.Hosting; using System; using System.Threading; using System.Threading.Tasks; // Custom HealthCheckResult that exposes degraded state metrics public class CustomHealthCheckResult : HealthCheckResult { public CustomHealthCheckResult(HealthStatus status, TimeSpan duration, string description = null, Exception exception = null, IReadOnlyDictionary<string, object> data = null) : base(status, description, exception, data) { Duration = duration; } public TimeSpan Duration { get; } } // Custom health check that exposes degraded state metrics public class CustomHealthCheck : IHealthCheck { private readonly IHostApplicationLifetime _lifetime; public CustomHealthCheck(IHostApplicationLifetime lifetime) { _lifetime = lifetime; } public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default) { try { // Simulate a health check that may take some time await Task.Delay(1000, cancellationToken); // Check if the application is shutting down if (_lifetime.ApplicationStopping.IsCancellationRequested) { // Return a degraded state if the application is shutting down return new CustomHealthCheckResult(HealthStatus.Degraded, TimeSpan.FromSeconds(1), "Application is shutting down"); } // Return a healthy state if the application is running normally return new CustomHealthCheckResult(HealthStatus.Healthy, TimeSpan.FromSeconds(1)); } catch (Exception ex) { // Return an unhealthy state if an exception occurs return new CustomHealthCheckResult(HealthStatus.Unhealthy, TimeSpan.FromSeconds(1), "An error occurred", ex); } } } // Register the custom health check with the IHealthCheckPublisher public class Startup { public void ConfigureServices(IServiceCollection services) { services.AddHealthChecks() .AddCheck<CustomHealthCheck>("custom_health_check"); services.AddSingleton<IHealthCheckPublisher, HealthCheckPublisher>(); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { app.UseRouting(); app.UseEndpoints(endpoints => { endpoints.MapHealthChecks("/health"); }); } } // HealthCheckPublisher that publishes health check results public class HealthCheckPublisher : IHealthCheckPublisher { private readonly ILogger<HealthCheckPublisher> _logger; public HealthCheckPublisher(ILogger<HealthCheckPublisher> logger) { _logger = logger; } public void PublishAsync(HealthReport report) { foreach (var entry in report.Entries) { var result = entry.Value; if (result.Status == HealthStatus.Degraded) { _logger.LogWarning($"Health check {entry.Key} is in a degraded state: {result.Description}"); } else if (result.Status == HealthStatus.Unhealthy) { _logger.LogError($"Health check {entry.Key} is in an unhealthy state: {result.Description}"); } else { _logger.LogInformation($"Health check {entry.Key} is healthy"); } } } } ``` This implementation includes a custom `CustomHealthCheckResult` class that exposes degraded state metrics, a custom `CustomHealthCheck` class that performs a health check and returns a `CustomHealthCheckResult`, and a `HealthCheckPublisher` class that publishes health check results. The `CustomHealthCheck` class simulates a health check that may take some time and checks if the application is shutting down. If the application is shutting down, it returns a degraded state. If an exception occurs, it returns an unhealthy state. The `HealthCheckPublisher` class publishes health check results by logging warnings for degraded states, errors for unhealthy states, and information for healthy states. The custom health check is registered with the `IHealthCheckPublisher` in the `Startup` class, and the `HealthCheckPublisher` is registered as a singleton instance. You can test the health check by visiting the `/health` endpoint, which will return a JSON response indicating the health status of the application.