NejCommon.NET/Health.cs

using System.Text.Json;
using Microsoft.AspNetCore.Diagnostics.HealthChecks;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using NejCommon.Utils;

namespace NejCommon;

public static class HealthUtils
{
    public static TBuilder AddDefaultHealthChecks<TBuilder>(this TBuilder builder) where TBuilder : IHostApplicationBuilder
    {
        builder.Services.AddHealthChecks()
            // ========================================
            // Kubernetes Probes
            // ========================================

            // Liveness Probe: "Is the application running?"
            // If it fails, Kubernetes RESTARTS the pod
            .AddCheck("self",
                () => HealthCheckResult.Healthy("Application is running"),
                tags: ["live"])

            // Readiness Probe: "Is the application ready to receive traffic?"
            // If it fails, Kubernetes REMOVES the pod from Service
            .AddCheck("readiness",
                () => HealthCheckResult.Healthy("Application is ready"),
                tags: ["ready"])

            // ========================================
            // Critical Dependencies (Database)
            // ========================================

            // PostgreSQL - Main database
            .Add(new HealthCheckRegistration(
                name: "postgres",
                factory: sp => new PostgresSqlHealthCheck(
                    sp.GetRequiredService<IConfiguration>(),
                    sp.GetRequiredService<ILogger<PostgresSqlHealthCheck>>(),
                    sp),
                failureStatus: HealthStatus.Degraded,  // Degraded allows app to continue
                tags: ["dependency", "critical", "database"],
                timeout: TimeSpan.FromSeconds(15)));

        // ========================================
        // Health Check Publisher (Periodic Checks)
        // ========================================

        builder.Services.Configure<HealthCheckPublisherOptions>(options =>
        {
            options.Delay = TimeSpan.FromSeconds(5);   // Wait 5s after startup
            options.Period = TimeSpan.FromSeconds(30); // Execute every 30s
        });

        return builder;
    }

    private static async Task WriteHealthCheckResponse(HttpContext context, HealthReport report)
    {
        context.Response.ContentType = "application/json";

        var response = new
        {
            Status = report.Status.ToString(),
            Timestamp = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ"),
            TotalDuration = $"{report.TotalDuration.TotalMilliseconds}ms",
            Results = report.Entries.Select(e => new
            {
                Name = e.Key,
                Status = e.Value.Status.ToString(),
                Duration = $"{e.Value.Duration.TotalMilliseconds}ms",
                Description = e.Value.Description,
                Error = e.Value.Exception?.Message,
                Data = e.Value.Data?.Count > 0 ? e.Value.Data : null,
                Tags = e.Value.Tags?.ToList()
            }).ToList(),
            Summary = new
            {
                Total = report.Entries.Count,
                Healthy = report.Entries.Count(e => e.Value.Status == HealthStatus.Healthy),
                Degraded = report.Entries.Count(e => e.Value.Status == HealthStatus.Degraded),
                Unhealthy = report.Entries.Count(e => e.Value.Status == HealthStatus.Unhealthy)
            }
        };

        await context.Response.WriteAsync(
            JsonSerializer.Serialize(response, new JsonSerializerOptions
            {
                WriteIndented = true,
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase
            }));
    }
    public static WebApplication MapHealthEndpoints(this WebApplication app)
    {
        var healthCheckOptions = new HealthCheckOptions
        {
            Predicate = _ => true,  // All dependencies
            ResponseWriter = WriteHealthCheckResponse,
            ResultStatusCodes = new Dictionary<HealthStatus, int>
            {
                [HealthStatus.Healthy] = StatusCodes.Status200OK,
                [HealthStatus.Degraded] = StatusCodes.Status200OK,
                [HealthStatus.Unhealthy] = StatusCodes.Status503ServiceUnavailable
            }
        };

        var liveOptions = new HealthCheckOptions
        {
            Predicate = r => r.Tags.Contains("live"),
            ResponseWriter = WriteHealthCheckResponse,
            ResultStatusCodes = new Dictionary<HealthStatus, int>
            {
                [HealthStatus.Healthy] = StatusCodes.Status200OK,
                [HealthStatus.Degraded] = StatusCodes.Status200OK,
                [HealthStatus.Unhealthy] = StatusCodes.Status503ServiceUnavailable
            }
        };

        var readyOptions = new HealthCheckOptions
        {
            Predicate = r => r.Tags.Contains("ready"),
            ResponseWriter = WriteHealthCheckResponse,
            ResultStatusCodes = new Dictionary<HealthStatus, int>
            {
                [HealthStatus.Healthy] = StatusCodes.Status200OK,
                [HealthStatus.Degraded] = StatusCodes.Status200OK,
                [HealthStatus.Unhealthy] = StatusCodes.Status503ServiceUnavailable
            }
        };

        // Map endpoints to both /health and /healthz (K8s compatibility)
        MapDetailedHealthEndpoints(app, "/health",
            healthCheckOptions, liveOptions, readyOptions);
        MapDetailedHealthEndpoints(app, "/healthz",
            healthCheckOptions, liveOptions, readyOptions);

        return app;
    }

    private static void MapDetailedHealthEndpoints(WebApplication app, string v, HealthCheckOptions healthCheckOptions, HealthCheckOptions liveOptions, HealthCheckOptions readyOptions)
    {
        app.MapHealthChecks(v, healthCheckOptions);
        app.MapHealthChecks(v + "/live", liveOptions);
        app.MapHealthChecks(v + "/ready", readyOptions);
    }
}