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.NET Core 3.0之深入源码理解HealthCheck(一)

写在前面

我们的系统可能因为正在部署、服务异常终止或者其他问题导致系统处于非健康状态,这个时候我们需要知道系统的健康状况,而健康检查可以帮助我们快速确定系统是否处于正常状态。一般情况下,我们会提供公开的HTTP接口,用于专门化健康检查。

NET Core提供的健康检查库包括Microsoft.Extensions.Diagnostics.HealthChecks.Abstractions和Microsoft.Extensions.Diagnostics.HealthChecks。这两个库共同为我们提供了最基础的健康检查的解决方案,后面扩展的组件主要有下面几个,本文不作其他说明。

AspNetCore.HealthChecks.System
AspNetCore.HealthChecks.Network
AspNetCore.HealthChecks.SqlServer
AspNetCore.HealthChecks.MongoDb
AspNetCore.HealthChecks.Npgsql
AspNetCore.HealthChecks.Redis
AspNetCore.HealthChecks.AzureStorage
AspNetCore.HealthChecks.AzureServiceBus
AspNetCore.HealthChecks.MySql
AspNetCore.HealthChecks.DocumentDb
AspNetCore.HealthChecks.SqLite
AspNetCore.HealthChecks.Kafka
AspNetCore.HealthChecks.RabbitMQ
AspNetCore.HealthChecks.IdSvr
AspNetCore.HealthChecks.DynamoDB
AspNetCore.HealthChecks.Oracle
AspNetCore.HealthChecks.Uris

源码探究

Microsoft.Extensions.Diagnostics.HealthChecks.Abstractions是.NET Core健康检查的抽象基础,从中我们可以看出这个库的设计意图。它提供了一个统一的接口IHealthCheck,用于检查应用程序中各个被监控组件的状态,包括后台服务、数据库等。这个接口只有一个方法CheckHealthAsync,

该方法有一个参数是HealthCheckContext,它表示当前健康检查执行时所关联的上下文对象,它的返回值HealthCheckResult表示当前健康检查结束后所产生的被监控组件的运行状态。

源码如下所示:

   1:  public interface IHealthCheck
   2:  {
   3:      Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default);
   4:  }

HealthCheckRegistration

HealthCheckContext里面只有一个成员就是HealthCheckRegistration实例。

HealthCheckRegistration是一个相当重要的对象,它体现了健康检查需要关注和注意的地方,其内部涉及到五个属性,分别用于:

  • 标识健康检查名称
  • 创建IHealthCheck实例
  • 健康检查的超时时间(防止我们因为健康检查而过多占用资源)
  • 失败状态标识
  • 一个标签集合(可用于健康检查过滤)

这五个属性的相关源码如下:

   1:  public Func<IServiceProvider, IHealthCheck> Factory
   2:  {
   3:      get => _factory;
   4:      set
   5:      {
   6:          if (value == null)
   7:          {
   8:              throw new ArgumentNullException(nameof(value));
   9:          }
  10:      
  11:          _factory = value;
  12:      }
  13:  }
  14:      
  15:  public HealthStatus FailureStatus { get; set; }
  16:      
  17:  public TimeSpan Timeout
  18:  {
  19:      get => _timeout;
  20:      set
  21:      {
  22:          if (value <= TimeSpan.Zero && value != System.Threading.Timeout.InfiniteTimeSpan)
  23:          {
  24:              throw new ArgumentOutOfRangeException(nameof(value));
  25:          }
  26:      
  27:          _timeout = value;
  28:      }
  29:  }
  30:      
  31:  public string Name
  32:  {
  33:      get => _name;
  34:      set
  35:      {
  36:          if (value == null)
  37:          {
  38:              throw new ArgumentNullException(nameof(value));
  39:          }
  40:      
  41:          _name = value;
  42:      }
  43:  }
  44:      
  45:  public ISet<string> Tags { get; }

 

HealthCheckResult

HealthCheckResult是一个结构体,可以看出这里更多的是基于承担数据存储和性能问题的考量。

HealthCheckResult用于表示健康检查的相关结果信息,同样的,通过该类,我们知道了健康检查需要关注的几个点:

  • 组件的当前状态
  • 异常信息
  • 友好的描述信息(不管是异常还是正常)
  • 额外可描述当前组件的键值对,这是一个开放式的属性,方面我们记录更多信息

该类含有四个公共属性,和三个方法,相关源码如下:

   1:  public struct HealthCheckResult
   2:  {
   3:      private static readonly IReadOnlyDictionary<string, object> _emptyReadOnlyDictionary = new Dictionary<string, object>();
   4:   
   5:      public HealthCheckResult(HealthStatus status, string description = null, Exception exception = null, IReadOnlyDictionary<string, object> data = null)
   6:      {
   7:          Status = status;
   8:          Description = description;
   9:          Exception = exception;
  10:          Data = data ?? _emptyReadOnlyDictionary;
  11:      }
  12:   
  13:      public IReadOnlyDictionary<string, object> Data { get; }
  14:   
  15:      public string Description { get; }
  16:   
  17:      public Exception Exception { get; }
  18:   
  19:      public HealthStatus Status { get; }
  20:   
  21:      public static HealthCheckResult Healthy(string description = null, IReadOnlyDictionary<string, object> data = null)
  22:      {
  23:          return new HealthCheckResult(status: HealthStatus.Healthy, description, exception: null, data);
  24:      }
  25:   
  26:      public static HealthCheckResult Degraded(string description = null, Exception exception = null, IReadOnlyDictionary<string, object> data = null)
  27:      {
  28:          return new HealthCheckResult(status: HealthStatus.Degraded, description, exception: exception, data);
  29:      }
  30:      
  31:      public static HealthCheckResult Unhealthy(string description = null, Exception exception = null, IReadOnlyDictionary<string, object> data = null)
  32:      {
  33:          return new HealthCheckResult(status: HealthStatus.Unhealthy, description, exception, data);
  34:      }
  35:  }

可以看出这个三个方法都是基于HealthStatus这个枚举而创建不同状态的HealthCheckResult实例,这个枚举表达了健康检查需要关注的几种状态,健康、异常以及降级。

HealthStatus的源码如下:

   1:  public enum HealthStatus
   2:  {
   3:      Unhealthy = 0,
   4:   
   5:      Degraded = 1,
   6:   
   7:      Healthy = 2,
   8:  }

IHealthCheckPublisher

健康检查功能本质上是一种轮询功能,需要定期执行,.NET Core 抽象定期执行的接口,即IHealthCheckPublisher,我们可以通过实现这个接口,并与我们自定义的定时功能相结合。

同时,作为一次健康检查,我们还需要关注相关的健康检查报告,那么我们需要关注那些点呢?

  • 额外可描述当前组件的键值对,这是一个开放式的属性,方面我们记录更多信息
  • 友好的描述信息(不管是异常还是正常)
  • 组件的当前状态
  • 异常信息
  • 当前这次检查所耗费的时间
  • 相关的标签信息

HealthReportEntry表示单个健康检查报告,HealthReport表示一组健康检查报告。HealthReport内部维护了一个HealthReportEntry的字典数据,HealthReport源码如下所示:

   1:  public sealed class HealthReport
   2:  {
   3:      public HealthReport(IReadOnlyDictionary<string, HealthReportEntry> entries, TimeSpan totalDuration)
   4:      {
   5:          Entries = entries;
   6:          Status = CalculateAggregateStatus(entries.Values);
   7:          TotalDuration = totalDuration;
   8:      }
   9:   
  10:      public IReadOnlyDictionary<string, HealthReportEntry> Entries { get; }
  11:   
  12:      public HealthStatus Status { get; }
  13:   
  14:      public TimeSpan TotalDuration { get; }
  15:   
  16:      private HealthStatus CalculateAggregateStatus(IEnumerable<HealthReportEntry> entries)
  17:      {
  18:          var currentValue = HealthStatus.Healthy;
  19:          foreach (var entry in entries)
  20:          {
  21:              if (currentValue > entry.Status)
  22:              {
  23:                  currentValue = entry.Status;
  24:              }
  25:   
  26:              if (currentValue == HealthStatus.Unhealthy)
  27:              {
  28:                  // Game over, man! Game over!
  29:                  // (We hit the worst possible status, so there's no need to keep iterating)
  30:                  return currentValue;
  31:              }
  32:          }
  33:   
  34:          return currentValue;
  35:      }
  36:  }

总结

通过以上内容,我们知道了,一个完整的健康检查需要关注健康检查上下文、健康状态的维护、健康检查结果、健康检查报告,同时,为了更好的维护健康检查,我们可以将健康检查发布抽象出来,并与外部的定时器相结合,共同守护健康检查程序。

本文转载自博客园,原文链接:https://www.cnblogs.com/edison0621/p/11968102.html

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