程序员开发程序，是“生”的过程，运维人员负责日常运维，是“养”的过程，在养的过程，运维人员希望在第一时间了解程序的状况，健康检查，是最基础的手段。
var builder = WebApplication.CreateBuilder(args);
//注入健康检查服务
builder.Services.AddHealthChecks();
var app = builder.Build();
app.MapGet("/test", () =>
{ return DateTime.Now;
});
//添加中间件，设置健康检查的访问路径是/health
app.MapHealthChecks("/health");
app.Run();
还可以通过重写来改变返回的字符串：
app.MapHealthChecks("/health", new HealthCheckOptions
{ResponseWriter = (context, result) =>{var backContent = "this is health";return context.Response.WriteAsync(backContent);}
});当然，这样的健康检查只是host有没有启动，如果有更深层次的检查，可以通过实现IHealthCheck来实现。
using Microsoft.Extensions.Diagnostics.HealthChecks;var builder = WebApplication.CreateBuilder(args);
//注入自定义健康检查类
builder.Services.AddHealthChecks().AddCheck<TestHealthCheck>("test_health_check");
var app = builder.Build();
app.MapGet("/test", () =>
{return DateTime.Now;
});
//添加中间件，设置健康检查的访问路径是/health
app.MapHealthChecks("/health");
app.Run();public class TestHealthCheck : IHealthCheck
{public Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default){//这是一个三方的获取空闲内存的库var client = new MemoryMetricsClient();var metrics = client.GetMetrics(); Console.WriteLine("Free : " + metrics.Free);//假业务要求，内存大于1000M，就健康var healthCheckResultHealthy = metrics.Free > 1000;if (healthCheckResultHealthy){return Task.FromResult(HealthCheckResult.Healthy("healthy"));}return Task.FromResult(new HealthCheckResult(context.Registration.FailureStatus,"unhealthy"));}
}有了这个实现，就可以很方便地实现业务中的各种判定服务是否健康了。
上面的所有健康检查都是拉模式，意思就是外部监控服务会请求本服务的/health，获取信息，来判定是否健康，在asp.net core也提供了推的模式，如下：
using Microsoft.Extensions.Diagnostics.HealthChecks;
using MiniDemo05;var builder = WebApplication.CreateBuilder(args);builder.Services.AddHealthChecks().AddCheck<TestHealthCheck>("test_health_check");
//配置推送的参数
builder.Services.Configure<HealthCheckPublisherOptions>(options =>
{options.Delay = TimeSpan.FromSeconds(1);options.Period = TimeSpan.FromSeconds(5);
});
//注入推送服务
builder.Services.AddSingleton<IHealthCheckPublisher, HealthPublisher>();var app = builder.Build();app.MapGet("/test", () =>
{return DateTime.Now;
});app.Run();public class TestHealthCheck : IHealthCheck
{public Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default){var client = new MemoryMetricsClient();var metrics = client.GetMetrics();Console.WriteLine("Total: " + metrics.Total);Console.WriteLine("Used : " + metrics.Used);Console.WriteLine("Free : " + metrics.Free);var healthCheckResultHealthy = metrics.Free > 6000;if (healthCheckResultHealthy){return Task.FromResult(HealthCheckResult.Healthy("healthy"));}return Task.FromResult(new HealthCheckResult(context.Registration.FailureStatus,"unhealthy"));}
}
public class HealthPublisher : IHealthCheckPublisher
{private readonly ILogger<HealthPublisher> _logger;public HealthPublisher(ILogger<HealthPublisher> logger){_logger = logger;}public Task PublishAsync(HealthReport report, CancellationToken cancellationToken){_logger.LogInformation($"{DateTime.Now.ToString()},{ report.Status}");return Task.CompletedTask;}
}如果监控参数收集是一个url，我们可以在HealthPublisher中把健康的结果推送上去。
