.NET Core下NLog读取Azure Blob连接串及日志异常排查

1. UpdateNLogConfig 方法调用位置 #

你需要在加载NLog配置之前，先完成appsettings配置的加载和GDC值的写入，正确调用位置如下：

public class Program
{
    public static void Main(string[] args)
    {
        // 第一步：先加载appsettings配置
        var config = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
            .Build();

        // 第二步：调用UpdateNLogConfig，将连接字符串存入GDC
        UpdateNLogConfig(config);

        // 第三步：再加载NLog配置，此时GDC已赋值可以正常读取
        var logger = NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
        try
        {
            logger.Debug("应用启动初始化");
            CreateHostBuilder(args).Build().Run();
        }
        catch (Exception exception)
        {
            logger.Error(exception, "程序因异常终止");
            throw;
        }
        finally
        {
            NLog.LogManager.Shutdown();
        }
    }

    // UpdateNLogConfig示例实现
    private static void UpdateNLogConfig(IConfiguration config)
    {
        // 从appsettings读取Blob连接字符串，key替换为你实际的配置项
        var blobConnStr = config.GetValue<string>("AzureBlobStorage:ConnectionString");
        // 存入GDC，key要和nlog.config里引用的${gdc:item=BlobConnectionString}保持一致
        NLog.GlobalDiagnosticsContext.Set("BlobConnectionString", blobConnStr);
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            })
            .ConfigureLogging(logging =>
            {
                logging.ClearProviders();
                logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
            })
            .UseNLog();
}

同步修改nlog.config里Blob target的connectionString属性为${gdc:item=BlobConnectionString}即可。

2. 切换到appsettings配置NLog后LocalTarget不生效的问题 #

当前代码和配置存在4个明显错误，逐一修正即可：

• 错误1：Program.cs中构建了nlogConfig但未传递给NLog，还是加载了默认空配置
• 错误2：JSON配置中路径使用了单斜杠\，未做转义，导致解析后路径错误
• 错误3：NLog的extensions配置格式错误，应为数组而非对象
• 错误4：JSON结构错误，targets节点的闭合括号缺失

修正后的Program.cs代码 #

public class Program
{
    public static void Main(string[] args)
    {
        var config = new ConfigurationBuilder()
            .SetBasePath(System.IO.Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
            .Build();

        // 直接将构建好的NLog配置赋值给LogManager
        NLog.LogManager.Configuration = new NLogLoggingConfiguration(config.GetSection("NLog"));
        var logger = NLog.LogManager.GetCurrentClassLogger();

        try
        {
            logger.Debug("Initialize main");
            CreateHostBuilder(args).Build().Run();
        }
        catch (Exception ex)
        {
            logger.Error(ex, "Stopped program because of exception.");
        }
        finally
        {
            NLog.LogManager.Shutdown();
        }
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            })
            .ConfigureLogging(logging =>
            {
                logging.ClearProviders();
                logging.SetMinimumLevel(Microsoft.Extensions.Logging.LogLevel.Trace);
            })
            // 告诉NLog使用已加载的配置，不要重新加载
            .UseNLog(config =>
            {
                config.Configuration = NLog.LogManager.Configuration;
                config.LoadConfigurationFromSection = false;
            });
}

修正后的appsettings.json配置 #

"NLog": {
  "internalLogLevel": "Info",
  "internalLogFile": "c:\\temp\\NLog\\internal-nlog.txt",
  "extensions": [
    { "assembly": "NLog.Web.AspNetCore" }
  ],
  "targets": {
    "LocalTarget": {
      "type": "File",
      "fileName": "c:\\temp\\NLog\\PayDocs_${shortdate}.log",
      "layout": "${longdate} | ${uppercase:${level}} | ${callsite} | ${message}"
    }
  },
  "rules": [
    {
      "logger": "Microsoft.*",
      "maxLevel": "Info",
      "final": "true"
    },
    {
      "logger": "*",
      "minLevel": "Trace",
      "writeTo": "LocalTarget"
    }
  ]
}

注：这里调整了规则顺序，优先过滤Microsoft前缀的日志，避免无效日志写入LocalTarget

内容的提问来源于stack exchange，提问作者Caverman