System.Diagnostics.Trace Application Logging Log Stream on Azure App Service Function App

By Benjamin Perkins · · , , ,

Here is what I wanted to do.

Add some code like this to my ASP.NET application.

using System.Diagnostics;
...
System.Diagnostics.Trace.WriteLine("System.Diagnostics.Trace.WriteLine() in the Page_Load method");
Trace.Write("Trace.Write() in the Page_Load method");
System.Diagnostics.Trace.TraceError("System.Diagnostics.Trace.TraceError() in the Page_Load method");
System.Diagnostics.Trace.TraceWarning("System.Diagnostics.Trace.TraceWarning() in the Page_Load method");
System.Diagnostics.Trace
       .TraceInformation("System.Diagnostics.Trace.TraceInformation() in the Page_Load method");

Then I wanted to write those logs out to the Application Logging (File System), Figure 1, Application Logging (Blob), Figure 2 and to the Log stream window in the portal, Figure 3.

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Figure 1, how to write System.Diagnostics.Trace logs to application logging (file system)

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Figure 2, how to write System.Diagnostics.Trace logs to application logging (blob)

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Figure 3, how to write System.Diagnostics.Trace logs to application Log stream

Obviously, you can see that I did it.  But how Benjamin, HOW!?  Well, first enable it, as seen in Figure 4.

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Figure 4, how to enable Application Logging to log System.Diagnostics.Trace

Then, the way I got this to work was to add the following to the top of the page which I wanted to log the traces from, Figure 5.

#define TRACE

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Figure 5, how to enable Application Logging to log System.Diagnostics.Trace

For other application types you may be required to enable the tracing in a different way.  If you have some examples please add a comment below.  However, the point I learned is that more than simply adding the System.Diagnostics.Trace() method wasn’t enough to get the logs to be output.