The correct option is Trace.TraceWarning("message").

Trace.TraceWarning emits a trace at the warning level which the tracing infrastructure and App Service diagnostic listeners recognize. That message will be recorded when the application's logging level is set to include warnings so it appears only at the warning threshold and above.

Trace.TraceInformation("message") is an information level trace and it will not be shown when logging is configured to only include warnings and errors because it is a lower severity than a warning.

Trace.WriteLine("message") writes a general trace string through trace listeners but it does not declare a warning level. It is treated as an untyped trace and will not be filtered or guaranteed to appear as a warning message.

Console.WriteLine("message") writes to standard output and is not tied to the trace severity levels. App Service may not capture or filter console output the same way as trace warnings so it will not reliably appear only when the logging level is set to warnings.

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