log4net items not shown in AppServiceAppLogs

Question

We are using log4net for our application logging in azure. We configured it according to this document , the logs are stored in

d:/home/LogFiles/Application/Log4netfile-[%processid].txt

we can download the files from https://xxxx.scm.azurewebsites.net/api/dump and I can also see them in Log stream, there it looks like this

2022-02-06T18:22:57  PID[29616] Verbose     log4net: Adding appender named [FileAppender] to logger [root].
2022-02-06T18:22:57  PID[29616] Verbose     log4net: Hierarchy Threshold []
2022-02-06T18:22:58  PID[29616] Verbose     LOG4NET Fatal LOG4NET LOG4NET
2022-02-06T18:22:58  PID[29616] Verbose     LOG4NET Debug Message Message

Line items like:

log4net: Adding appender named  

are created by log4net during internal setup (using debug=true), and those show up in our AppServiceAppLogs, however, items which are genereted by the logger using:

Logger.Fatal("LOG4NET Fatal LOG4NET LOG4NET");

are visible in stream and files but they are not showing up in AppServiceLogs.

I tried multiple different appenders the only one which shows up in Log-Streams and in files is FileAppender (or RollingFileAppender), all others are not showing in LogStreams or (as expected) in the files.

Based on this https://learn.microsoft.com/en-us/azure/app-service/troubleshoot-diagnostic-logs#send-logs-to-azure-monitor I assume that everything writen to the files should be than sent to azure-monitor - but in our case this is not hapening. Could you provide some reference about implementation / code how the sending of the files is done, and which process does that ?

I am wandering is there anything which we could configure differently to get the log-items to end up in AppServiceLogs? Or should we use some other appender?

I am aware of the issue in AspNetTraceAppender and I am trying to avoid implementation of new appender.

Answer 1

There are a few things you can look into:

Call log4net configure before writing to your log file (only once is enough):

log4net.Config.XmlConfigurator();

or

log4net.Config.XmlConfigurator.Configure();

and then you can add flushing to your configuration:

<appender name="AzureTraceAppender" type="log4net.Appender.TraceAppender">
  <param name="ImmediateFlush" value="true" />
  <layout type="log4net.Layout.PatternLayout">
    <!-- can be any pattern you like -->
    <conversionPattern value="%logger - %message" />
  </layout>
</appender>

Immediately, this will flush the message.

In Global.asax, To make log4net read your configuration.

void Application_Start(object sender, EventArgs e) 
{
    // Code that runs on application startup

    // Initialize log4net.
    log4net.Config.XmlConfigurator.Configure();
}

Make sure Azure Diagnostics has configured to all information needed for debugging.

After that, you can enable internal log4net debugging. Refer internal debugging on this log4net faq page. Standard it should log to your listener you have configured. To the trace element Add the autoflush="true" option . Or find directory on the worker role you can write to and access to read your logs.