Asp.net 核心健康检查随机失败并出现 TaskCanceledException 或 OperationCanceledException

Question

我已经在我的 asp.net 核心应用程序中实现了健康检查。 一项运行状况检查执行 2 项检查 - DbContext 连接和自定义一项检查 NpgsqlConnection。

在超过 99% 的情况下一切正常。有时运行状况检查失败并抛出 TaskCanceledException 或 OperationCanceledException。从我的日志中，我可以看到这个异常是在大约 2ms​​-25ms 后引发的（所以不可能发生任何超时）。

重要提示：

当我多次点击 healthchecks（浏览器中的简单 F5）时，它会引发异常。在之前的健康检查完成之前，您似乎无法点击 /health 端点。如果是这种情况 - 为什么？即使我将 Thread.Sleep(5000); 放入自定义运行状况检查（根本没有数据库连接检查），如果我在 5 秒过去之前点击 /health 端点，它也会失败。

问题：healtheck 是否以某种方式“神奇地”单线程（当您再次点击该端点时，它会取消先前的 healthcheck 调用）？

Startup.cs 配置服务

services
    .AddHealthChecks()
    .AddCheck<StorageHealthCheck>("ReadOnly Persistance")
    .AddDbContextCheck<MyDbContext>("EFCore persistance");

Startup.cs 配置

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}
else
{
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseCors(options => options.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader());

app.UseMiddleware<RequestLogMiddleware>();
app.UseMiddleware<ErrorLoggingMiddleware>();

if (!env.IsProduction())
{
    app.UseSwagger();

    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "V1");
        c.SwaggerEndpoint($"/swagger/v2/swagger.json", $"V2");
    });
}

app.UseHealthChecks("/health", new HealthCheckOptions()
{
    ResponseWriter = WriteResponse
});

app.UseMvc();

StorageHealthCheck.cs

public class StorageHealthCheck : IHealthCheck
    {
        private readonly IMediator _mediator;

        public StorageHealthCheck(IMediator mediator)
        {
            _mediator = mediator;
        }

        public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken = default(CancellationToken))
        {
            var isReadOnlyHealthy = await _mediator.Send(new CheckReadOnlyPersistanceHealthQuery());

            return new HealthCheckResult(isReadOnlyHealthy ? HealthStatus.Healthy : HealthStatus.Unhealthy, null);
        }
    }

CheckReadOnlyPersistanceHealthQueryHandler：

NpgsqlConnectionStringBuilder csb = new NpgsqlConnectionStringBuilder(_connectionString.Value);

string sql = $@"
    SELECT * FROM pg_database WHERE datname = '{csb.Database}'";

try
{
    using (IDbConnection connection = new NpgsqlConnection(_connectionString.Value))
    {
        connection.Open();

        var stateAfterOpening = connection.State;
        if (stateAfterOpening != ConnectionState.Open)
        {
            return false;
        }

        connection.Close();
        return true;
    }
}
catch
{
    return false;
}

TaskCanceledException：

System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at Npgsql.TaskExtensions.WithCancellation[T](Task`1 task, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnector.ConnectAsync(NpgsqlTimeout timeout, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnector.RawOpen(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnector.Open(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnection.<>c__DisplayClass32_0.<<Open>g__OpenLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlDatabaseCreator.ExistsAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Diagnostics.HealthChecks.DbContextHealthCheck`1.CheckHealthAsync(HealthCheckContext context, CancellationToken cancellationToken)
   at Microsoft.Extensions.Diagnostics.HealthChecks.DefaultHealthCheckService.CheckHealthAsync(Func`2 predicate, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Diagnostics.HealthChecks.HealthCheckMiddleware.InvokeAsync(HttpContext httpContext)
   at Microsoft.AspNetCore.Builder.Extensions.MapWhenMiddleware.Invoke(HttpContext context)

操作取消​​异常：

System.OperationCanceledException: The operation was canceled.
   at System.Threading.CancellationToken.ThrowOperationCanceledException()
   at Microsoft.Extensions.Diagnostics.HealthChecks.DefaultHealthCheckService.CheckHealthAsync(Func`2 predicate, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Diagnostics.HealthChecks.HealthCheckMiddleware.InvokeAsync(HttpContext httpContext)
   at Microsoft.AspNetCore.Builder.Extensions.MapWhenMiddleware.Invoke(HttpContext context)

Answer 1

我终于找到答案了。

最初的原因是当HTTP请求中止时，然后httpContext.RequestAbortedCancellationToken被触发，并抛出异常（OperationCanceledException）。

我的应用程序中有一个全局异常处理程序，并且我一直将每个未处理的异常转换为 500 错误。即使客户端中止了请求，并且从未收到 500 响应，我的日志仍然记录了这一点。

我实现的解决方案是这样的：

public async Task Invoke(HttpContext context)
{
    try
    {
        await _next(context);
    }
    catch (Exception ex)
    {
        if (context.RequestAborted.IsCancellationRequested)
        {
            _logger.LogWarning(ex, "RequestAborted. " + ex.Message);
            return;
        }

        _logger.LogCritical(ex, ex.Message);
        await HandleExceptionAsync(context, ex);
        throw;
    }
}

private static Task HandleExceptionAsync(HttpContext context, Exception ex)
{
    var code = HttpStatusCode.InternalServerError; // 500 if unexpected

    //if (ex is MyNotFoundException) code = HttpStatusCode.NotFound;
    //else if (ex is MyUnauthorizedException) code = HttpStatusCode.Unauthorized;
    //else if (ex is MyException) code = HttpStatusCode.BadRequest;

    var result = JsonConvert.SerializeObject(new { error = ex.Message });
    context.Response.ContentType = "application/json";
    context.Response.StatusCode = (int)code;
    return context.Response.WriteAsync(result);
}

希望对某人有所帮助。

Answer 2

在大型生产环境中进行测试后，我最好的理论是，您需要在健康检查中等待任何写入 http 上下文输出流的写入器。我在返回未等待的任务的方法中遇到此错误。等待任务似乎已经解决了问题。 await 的好处在于，您还可以捕获 TaskCancelledException 并直接吃掉它。

例子：

// map health checks
endpoints.MapHealthChecks("/health-check", new HealthCheckOptions
{
    ResponseWriter = HealthCheckExtensions.WriteJsonResponseAsync,
    Predicate = check => check.Name == "default"
});

/// <summary>
/// Write a json health check response
/// </summary>
/// <param name="context">Http context</param>
/// <param name="report">Report</param>
/// <returns>Task</returns>
public static async Task WriteJsonResponseAsync(HttpContext context, HealthReport report)
{
    try
    {
        HealthReportEntry entry = report.Entries.Values.FirstOrDefault();
        context.Response.ContentType = "application/json; charset=utf-8";
        await JsonSerializer.SerializeAsync(context.Response.Body, entry.Data,entry.Data.GetType());
    }
    catch (TaskCancelledException)
    {
    }
}