ASP.NET Core API中Application Insights缺失日志条目问题求助

问题现象 #

使用Application Insights监控ASP.NET Core Web API时，发现代码中按顺序执行的两条LogInformation日志，仅"edit order: ending handling request"条目被记录，"edit order: start handling request"条目缺失。

相关代码片段 #

命令处理类代码 #

public class EditOrderCommandHandler : IRequestHandler<EditOrderCommand, EditOrderResponseStatus>
{
    readonly ILogger<EditOrderCommandHandler> _logger;
    readonly CqgHostService _cqgHostService;

    public EditOrderCommandHandler(ILogger<EditOrderCommandHandler> logger, CqgHostService cqgHostService)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _cqgHostService = cqgHostService;
    }

    public async Task<EditOrderResponseStatus> Handle(EditOrderCommand request, CancellationToken cancellationToken)
    {
        _logger.LogInformation($"edit order: start handling request: {request.SerializeObject()} -- at: {DateTime.UtcNow}");
        await _cqgHostService.SendEditOrderAsync(request.AccountId, request.ClOrderId, request.Qty, request.LimitPrice,
            request.StopPrice, request.Duration, request.TenantId, request.OnBehalfOf);

        var editOrderResponseStatus = new EditOrderResponseStatus();
        _logger.LogInformation($"edit order: ending handling request: {request.SerializeObject()} -- at: {DateTime.UtcNow}");
        return await Task.FromResult(editOrderResponseStatus);
    }
}

日志配置代码 #

builder.Logging
    .AddApplicationInsights(builder.Configuration.ApplicationInsightsInstrumentationKey())
    .AddFilter<ApplicationInsightsLoggerProvider>(typeof(Program).FullName, LogLevel.Trace)
    .AddFilter<ApplicationInsightsLoggerProvider>(typeof(Startup).FullName, LogLevel.Trace)
    .AddFilter<ApplicationInsightsLoggerProvider>("", LogLevel.Information)
    .AddFilter<ApplicationInsightsLoggerProvider>("Microsoft", LogLevel.Information)
    .AddFilter<ApplicationInsightsLoggerProvider>("Default", LogLevel.Information);

查询语句与结果 #

初始Kusto查询 #

traces
| where timestamp >= datetime('2023-10-12T17:24:00Z') and timestamp <= datetime('2023-10-12T17:26:00Z')
| where message contains "edit order"
| project timestamp, message, customDimensions, operation_Id
| order by timestamp desc

查询结果 #

2023-10-12T17:25:50.8118518Z
edit order: ending handling request: {"ClOrderId":"OHPW-1745-00622_24582026746","Duration":2,"Qty":{"Significand":1,"HasSignificand":true,"Exponent":0,"HasExponent":true},"LimitPrice":5.2350,"StopPrice":0,"CreationDate":"2023-10-12T12:25:50.6475684-05:00","Instrument":"F.US.ZCEZ24","TenantId":"2347ef30-a972-4c99-ac2f-23e4c971adad","AccountId":1769007,"OnBehalfOf":"JBenson2"} -- at: 10/12/2023 5:25:50 PM

补充排查操作 #

执行采样率检查的Kusto查询：

union requests, dependencies, pageViews, browserTimings, exceptions, traces
| where timestamp >= datetime('2023-10-12T17:24:00Z') and timestamp <= datetime('2023-10-12T17:26:00Z')
| summarize RetainedPercentage = 100 / avg(itemCount) by bin(timestamp, 1h), itemType
| order by itemType, timestamp asc

查询结果：

原因分析与解决方案 #

原因定位 #

从采样率查询结果可见，traces类型日志的保留率仅为10%，说明Application Insights启用了自适应采样。自适应采样会根据系统流量自动调整采样比例，流量高峰时部分Information级别日志会被随机丢弃，导致启动日志未被采集。

解决方案建议 #

1. 全局禁用自适应采样
   在appsettings.json中配置固定100%采样率：

{
  "ApplicationInsights": {
    "Sampling": {
      "AdaptiveSamplingEnabled": false,
      "FixedRateSamplingPercentage": 100
    }
  }
}

2. 针对特定日志保留采样
   如果需要保留采样机制但确保关键日志不丢失，可添加自定义采样筛选器，强制保留EditOrderCommandHandler相关日志：

builder.Services.Configure<TelemetryConfiguration>(config =>
{
    var samplingProcessor = config.DefaultTelemetrySink.TelemetryProcessors
        .OfType<AdaptiveSamplingTelemetryProcessor>()
        .FirstOrDefault();
    
    if (samplingProcessor != null)
    {
        // 自定义筛选逻辑：包含包含"edit order"的日志
        config.TelemetryProcessors.Add(new CustomTraceSamplingProcessor(samplingProcessor));
    }
});

// 自定义采样处理器示例
public class CustomTraceSamplingProcessor : ITelemetryProcessor
{
    private readonly ITelemetryProcessor _nextProcessor;

    public CustomTraceSamplingProcessor(ITelemetryProcessor nextProcessor)
    {
        _nextProcessor = nextProcessor;
    }

    public void Process(ITelemetry item)
    {
        if (item is TraceTelemetry trace && trace.Message.Contains("edit order"))
        {
            // 强制保留该日志
            item.Context.SamplingPercentage = 100;
        }
        _nextProcessor.Process(item);
    }
}

3. 确保日志发送完成
   日志异步发送时，若应用在日志发送前终止可能导致丢失，可在请求结束时等待日志发送完成：

app.Use(async (context, next) =>
{
    await next();
    var telemetryClient = context.RequestServices.GetRequiredService<ITelemetryClient>();
    await telemetryClient.FlushAsync();
    await Task.Delay(500); // 给足够时间完成日志发送
});

内容的提问来源于stack exchange，提问作者nop