.net core使用NLog+Elasticsearch记录日志

     在微服务或分布式系统中，如果将日志作为文件输出，查看系统日志将非常不便；如果将日志保存到数据库中，又不能进行全文搜索。在这里我们将日志输出到ElasticSearch中，借助Kibana再查找日志。

添加Nuget引用

       需要添加两个Nuget引用：NLog.Web.AspNetCore和NLog.Targets.ElasticSearch

配置

       新增nlog.config配置文件，并设置属性生成操作为内容，复制到输出目录为始终复制，内容如下。

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      internalLogToConsole="true">
  <extensions>
    <add assembly="NLog.Targets.ElasticSearch"/>
  </extensions>

  <targets>
    <!--ElasticSearch保存日志信息-->
    <target name="ElasticSearch" xsi:type="ElasticSearch" ConnectionStringName="ElasticSearchServerAddress"  
            index="userapi-${date:format=yyyy.MM.dd}" documentType="doc" includeAllProperties="true"
                 layout="[${date:format=yyyy-MM-dd HH:mm:ss}][${level}] ${logger} ${message} ${exception:format=toString}">
      <field name="MachineName" layout="${machinename}" />
      <field name="Time" layout="${longdate}" />
      <field name="level" layout="${level:uppercase=true}" />
      <field name="logger" layout=" ${logger}" />
      <field name="message" layout=" ${message}" />
      <field name="exception" layout=" ${exception:format=toString}" />
      <field name="processid" layout=" ${processid}" />
      <field name="threadname" layout=" ${threadname}" />
      <field name="stacktrace" layout=" ${stacktrace}" />
      <field name="Properties" layout="${machinename} ${longdate} ${level:uppercase=true} ${logger} ${message} ${exception}|${processid}|${stacktrace}|${threadname}" />
    </target>
  </targets>
  <rules>
    <logger name="*" minlevel="INFO" writeTo="ElasticSearch" />
  </rules>
</nlog>

      修改appsettings.json，增加如下节点，注意，经调试源码才发现，这里必须将连接增加到ConnectionStrings节点下，ElasticSearchServerAddress节点名称对应nlog.config中ConnectionStringName的名称。

"ConnectionStrings": {
    "ElasticSearchServerAddress": "http://192.168.2.97:9200,http://192.168.2.101:9200,http://192.168.2.102:9200"
}

修改代码

     修改Program.cs文件：

public static void Main(string[] args)
{
      NLogBuilder.ConfigureNLog("nlog.config");
      BuildWebHost(args).Run();
 }

public static IWebHost BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseNLog()
                .UseStartup<Startup>()
                .Build();

　　修改Startup.cs文件：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
   loggerFactory.AddNLog();
}

测试

    public class ValuesController : Controller
    {
        private ILogger _logger;

        public ValuesController(ILogger<ValuesController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IEnumerable<string> Get()
        {
            _logger.LogInformation("测试一下，不要紧张!");
            return new string[] { "value1", "value2" };
        }
}

      kibana里查询截图：