如何在.NET Core 6.0中配置NLog的Azure Event Hub目标（AppSettings版）

使用NLog.Extensions.AzureEventHub连接Azure Event Hub时配置出错，传入连接字符串参数仍报错，官方文档仅提供XML配置示例，需要适用于C# .NET Core 6.0的AppSettings配置示例。

原有配置 #

"NLog":{
"internalLogLevel":"Info",
"internalLogFile":"c:\\temp\\internal-nlog.txt",
"extensions": [
  { "assembly": "NLog.Extensions.Logging" },
  { "assembly": "NLog.Web.AspNetCore" },
  { "assembly": "NLog.Extensions.AzureEventHub" }
],
"targets": {
  "allfile": {
    "type": "File",
    "fileName": "c:\\temp\\nlog-all-${shortdate}.log",
    "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}"
  },
  "ownFile-web": {
    "type": "File",
    "fileName": "c:\\temp\\nlog-own-${shortdate}.log",
    "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}"
  },

  "eh": {
    "type": "AzureEventHub",
    "credentials": {
      "name": "eventhub1",
      "connectionString": "Endpoint=sb://eventhubnp198007.servicebus.windows.net/;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=4z/JbjHp7UqxCWPD343434343GZbJpfG5E="
    },
    "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}"
  }

},
"rules":[
    {
        "logger":"*",
        "minLevel":"Trace",
        "writeTo":"allfile"
    },
    {
        "logger":"Microsoft.*",
        "maxLevel":"Info",
        "final":"true"
    },
    {
        "logger":"*",
        "minLevel":"Trace",
        "writeTo":"ownFile-web"
    }
]
}

报错信息 #

2022-08-23 12:59:10.0781 Error AzureEventHub(Name=eh): Failed to
create EventHubClient with connectionString= to EventHubName=.
Exception: System.ArgumentException: Value cannot be an empty string.
(Parameter 'connectionString') at
Azure.Core.Argument.AssertNotNullOrEmpty(String value, String name)
at
Azure.Messaging.EventHubs.Producer.EventHubProducerClient..ctor(String
connectionString, String eventHubName, EventHubProducerClientOptions
clientOptions) at
NLog.Targets.EventHubTarget.EventHubService.Connect(String
connectionString, String eventHubName, String serviceUri, String
tenantIdentity, String resourceIdentity, String clientIdentity) at
NLog.Targets.EventHubTarget.InitializeTarget()

错误原因是AzureEventHub目标的配置参数结构不符合组件要求，JSON配置无需嵌套credentials对象，直接将参数作为目标的一级属性即可。

修改后的完整AppSettings配置：

{
  "NLog":{
    "internalLogLevel":"Info",
    "internalLogFile":"c:\\temp\\internal-nlog.txt",
    "extensions": [
      { "assembly": "NLog.Extensions.Logging" },
      { "assembly": "NLog.Web.AspNetCore" },
      { "assembly": "NLog.Extensions.AzureEventHub" }
    ],
    "targets": {
      "allfile": {
        "type": "File",
        "fileName": "c:\\temp\\nlog-all-${shortdate}.log",
        "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}"
      },
      "ownFile-web": {
        "type": "File",
        "fileName": "c:\\temp\\nlog-own-${shortdate}.log",
        "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}"
      },
      "eh": {
        "type": "AzureEventHub",
        "eventHubName": "eventhub1",
        "connectionString": "Endpoint=sb://eventhubnp198007.servicebus.windows.net/;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=4z/JbjHp7UqxCWPD343434343GZbJpfG5E=",
        "layout": "${longdate}|${event-properties:item=EventId_Id}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}|url: ${aspnet-request-url}|action: ${aspnet-mvc-action}"
      }
    },
    "rules":[
      {
        "logger":"*",
        "minLevel":"Trace",
        "writeTo":"allfile"
      },
      {
        "logger":"Microsoft.*",
        "maxLevel":"Info",
        "final":"true"
      },
      {
        "logger":"*",
        "minLevel":"Trace",
        "writeTo":"ownFile-web"
      },
      {
        "logger":"*",
        "minLevel":"Trace",
        "writeTo":"eh"
      }
    ]
  }
}

关键修改点 #

• 移除credentials嵌套对象，将eventHubName（对应原配置中的name）和connectionString作为eh目标的一级配置项
• 在rules中添加日志写入Azure Event Hub的规则（原配置缺少此规则，即使目标配置正确也不会有日志输出）

报错原因说明 #

原配置使用的credentials嵌套结构并非NLog.Extensions.AzureEventHub的JSON配置支持的格式，导致组件无法读取到connectionString和eventHubName参数，从而抛出空字符串异常。

内容的提问来源于stack exchange，提问作者sansalk