Azure Functions v4 InProcess模式下host.json采样设置未生效求助

问题场景 #

使用.NET6 InProcess模式的Azure Functions v4，尝试通过host.json配置Application Insights仅对依赖项进行采样收集，但配置未生效：

当前host.json配置：

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "includedTypes": "Dependency"
      }
    }
  }
}

预期仅收集依赖项数据，但实际无效果。尝试设置enableDependencyTracking: false会完全停止依赖项收集，不符合需求。项目配置如下：

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Azure.Functions.Extensions" Version="1.1.0" />
    <PackageReference Include="Microsoft.Azure.WebJobs.Extensions.ServiceBus" Version="5.11.0" />
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="4.2.0" />
    <PackageReference Include="Microsoft.Extensions.Http" Version="6.0.0" />
    <PackageReference Include="Microsoft.Extensions.Http.Polly" Version="6.0.18" />
    <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
</Project>

排查与解决方法 #

1. 修正采样配置逻辑 #

includedTypes的作用是指定哪些类型日志会进入采样评估流程，而非仅保留该类型数据。默认采样会关联请求链路，若父请求被采样排除，依赖项作为子项也会被过滤。要实现仅收集依赖项，需明确排除其他类型并确保依赖项采样率：

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "includedTypes": "Dependency",
        "excludedTypes": "Request;Trace;Exception;Event",
        "percentage": 100
      },
      "enableDependencyTracking": true
    }
  }
}

• 明确排除请求、追踪等其他日志类型
• 设置percentage:100确保所有依赖项都被采样（可按需调整比例）

2. 升级依赖包版本 #

当前使用的Microsoft.NET.Sdk.Functions 4.2.0版本存在Application Insights采样逻辑的已知问题，建议升级至较新版本（如4.11.0及以上），同步更新相关依赖：

<PackageReference Include="Microsoft.NET.Sdk.Functions" Version="4.11.0" />
<PackageReference Include="Microsoft.Azure.WebJobs.Extensions.ServiceBus" Version="5.17.0" />

3. 检查环境采样设置冲突 #

• 本地调试时，需确保local.settings.json未强制关闭采样：

{
  "Values": {
    "APPINSIGHTS_INSTRUMENTATIONKEY": "你的密钥",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    "APPINSIGHTS_SAMPLING_PERCENTAGE": "100"
  }
}

• 部署到Azure后，检查Application Insights门户中的采样设置是否覆盖了host.json配置，门户设置优先级更高。

4. 确认HttpClient依赖追踪正确性 #

若使用自定义HttpClient发起请求，必须通过依赖注入方式创建实例，而非直接new HttpClient()，否则依赖追踪无法正常捕获请求：

public class MyFunction
{
    private readonly HttpClient _httpClient;
    public MyFunction(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    [FunctionName("MyFunction")]
    public async Task Run([ServiceBusTrigger("queue", Connection = "ServiceBusConnection")] string myQueueItem)
    {
        await _httpClient.GetAsync("https://example.com");
    }
}

内容的提问来源于stack exchange，提问作者klucyszy