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.Net C# Logging NLog

NLog FallbackGroup Target

In the past I have written few blog posts on NLog and discussed several techniques:

Programatically configuring NLog in C#

NLog in .Net Applications

Some NLog configuration examples for writing into different log management systems

How to log debug level logs only when an exception occurs in ASP.Net using NLog

And I have discussed about a possibility of capturing more information in logs only when needed such as in the case of errors or exceptions in the following blog post:

An abnormal way of logging – open for discussion

My use-case explanation:

I am planning to use Gelf logging for easier compatibility reasons. Gelf logs can be ingested into pretty much every major centralized logging platforms such as: Kibana, GrayLog, Seq, Grafana. Some would require some intermediary software to accept Gelf formatted logs and some can directly ingest Gelf formatted logs. However, for various reasons, sometimes the logging server might not be available, specifically when the log ingestors are not in a cluster. Log files can be easily ingested into the above mentioned centralized logging agents using different sofware.

Based on the above use-case I wanted to use Gelf for directly logging into the centralized logging server and as a failover, I want to write the logs to a file that would get ingested at a later point by some other software.

Now, by combing the previous post example, we can achieve AspNetBuffering and ingest different levels of logs only when errors occur. The code samples should be very easy to understand.

Read the How to log debug level logs only when an exception occurs in ASP.Net using NLog prior to continuing.

    <add assembly="NLog.Web.AspNetCore"/>
    <add assembly="NLog.Targets.Gelf"/>

    <target xsi:type="AspNetBufferingWrapper" name="aspnetbuffer" bufferGrowLimit="100000" growBufferAsNeeded="true">
        <target xsi:type="PostFilteringWrapper" defaultFilter="level &gt;= LogLevel.Info">
            <target xsi:type="FallbackGroup" returnToFirstOnSuccess="true">
                <target xsi:type="gelf" endpoint="tcp://logs.local:12201" facility="console-runner" sendLastFormatParameter="true">
                    <parameter name="param1" layout="${longdate}"/>
                    <parameter name="param2" layout="${callsite}"/>
		<target xsi:type="File" fileName="c:\temp\nlog-AspNetCore-all-${shortdate}.log" layout="${longdate}|${event-properties:item=EventId:whenEmpty=0}|${level:uppercase=true}|${logger}|${message} ${exception:format=tostring}" />
              <when exists="level &gt;= LogLevel.Warn" filter="level &gt;= LogLevel.Debug"/>

    <logger name="*" minlevel="Debug" writeTo="aspnetbuffer" />

In the above code we have wrapped Gelf logger, File logger inside a FallBackGroup logger. The FallBackGroup logger is wrapped inside a PostFilteringWrapper. The PostFilteringWrapper is wrapped inside a AspNetBufferingWrapper.

In the above code in the <rules> section we are sending all Debug and above logs to the AspNetBufferingWrapper.

Now AspNetBufferingWrapper buffers the log messages for an entire request, response cycle and sends the log messages to the PostFilteringWrapper.

The PostFilteringWrapper sees if there are any Warnings or above loglevel, if yes sends all the messages that have Debug and above loglevels. Else sends Info and above messages. The target of PostFilteringWrapper is the FallbackGroup logger which receives these messages.

The FallBackGroup logger attempts to use the Gelf logger, if the Gelf logger is unable to process the messages, the logs are sent to the File logger.

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Mr. Kanti Kalyan Arumilli

Arumilli Kanti Kalyan, Founder & CEO
Arumilli Kanti Kalyan, Founder & CEO

B.Tech, M.B.A






Founder & CEO, Lead Full-Stack .Net developer

ALight Technology And Services Limited

ALight Technologies USA Inc




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