Reporting Service for Microsoft.Extensions.Diagnostics.HealthChecks -> App Metrics

HealthMetricsHostedService.cs

using App.Metrics;
using App.Metrics.Gauge;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace JonasMH.AspNetCore
{
	public class HealthMetricsHostedService : IHostedService
	{
		public static readonly string Context = "Application.Health";

		public static GaugeOptions Checks => new GaugeOptions
		{
			Context = Context,
			Name = "Results",
			MeasurementUnit = Unit.Items
		};

		private readonly HealthCheckService _healthCheckService;
		private System.Timers.Timer _timer;
		private readonly ILogger<HealthMetricsHostedService> _logger;
		private readonly IMetrics _metrics;

		public HealthMetricsHostedService(
			HealthCheckService healthCheckService,
			ILogger<HealthMetricsHostedService> logger,
			IMetrics metrics)
		{
			_healthCheckService = healthCheckService;
			_logger = logger;
			_metrics = metrics;
		}

		public Task StartAsync(CancellationToken cancellationToken)
		{
			_logger.LogInformation("Health metrics service started");
			DoWork(cancellationToken);

			_timer = new System.Timers.Timer();
			_timer.Elapsed += (sender, e) => DoWork(cancellationToken);
			_timer.Interval = TimeSpan.FromSeconds(30).TotalMilliseconds;
			_timer.Start();

			return Task.CompletedTask;
		}

		public Task StopAsync(CancellationToken cancellationToken)
		{
			_logger.LogInformation("Health metrics service stopped");
			_timer.Stop();
			_timer.Dispose();

			return Task.CompletedTask;
		}

		private Task DoWork(CancellationToken cancellationToken) {
			return Task.Run(async () => await SendUpdates(cancellationToken), cancellationToken);
		}

		private async Task SendUpdates(CancellationToken cancellationToken)
		{
			_logger.LogInformation("Getting healthchecks");

			var result = await _healthCheckService.CheckHealthAsync(cancellationToken);

			foreach (var item in result.Entries)
			{
				var tags = new MetricTags("health_check_name", item.Key);
				float healthScore = -1;

				switch (item.Value.Status)
				{
					case HealthStatus.Healthy:
						healthScore = 1f;
						break;
					case HealthStatus.Degraded:
						healthScore = 0.5f;
						break;
					case HealthStatus.Unhealthy:
						healthScore = 0f;
						break;
					default:
						_logger.LogWarning($"Healthcheck '${item.Key}' did not have a known service status ${item.Value.Status.ToString()}");
						continue;
				}

				_metrics.Measure.Gauge.SetValue(Checks, tags, healthScore);
			}

			_timer.Interval = TimeSpan.FromSeconds(30).TotalMilliseconds;
			_timer.Start();
		}
	}
}

Startup.cs

[...]
namespace JonasMH.AspNetCore
{
	public class Startup
	{
		[...]

		// This method gets called by the runtime. Use this method to add services to the container.
		public void ConfigureServices(IServiceCollection services)
		{
			[...]

			// Add you own health checks or use https://github.com/xabaril/AspNetCore.Diagnostics.HealthChecks as I did here
			services
				.AddHealthChecks();
				//.AddNpgSql(connectionString) 
				//.AddElasticsearch("http://elasticsearch:9200")

			// Register service
			services.AddHostedService<HealthMetricsHostedService>();
			
			[...]
		}
		
		[...]
	}
}