Logging from ASP.NET 5 application hosted as Azure Web App

Question

I have an ASP.NET 5 Web API that I host in Azure as a Web App. I want to log messages from my code using Azure Diagnostics. There are multiple article including Azure docs that suggest that it should be as easy as System.Diagnostics.Trace.WriteLine once enabled. The logs should show up under LogsFiles/Application and in log stream in Azure.

I enabled application logging for the web app:

But the following calls produces no logs:

System.Diagnostics.Trace.TraceError("TEST");
System.Diagnostics.Trace.TraceInformation("TEST");
System.Diagnostics.Trace.TraceWarning("TEST");
System.Diagnostics.Trace.WriteLine("TEST");

I tried to manually define TRACE symbol, but with no luck:

I also tried to use the new Microsoft.Extensions.Logging framework and use ILogger.Log API, but without any results again:

public void Configure(IApplicationBuilder app, 
                      IHostingEnvironment env, 
                      ILoggerFactory loggerFactory)
{
    loggerFactory.MinimumLevel = LogLevel.Debug;

    var sourceSwitch = new SourceSwitch("Sandbox.AspNet5.ApiApp-Demo");
    sourceSwitch.Level = SourceLevels.All;
    loggerFactory.AddTraceSource(sourceSwitch, 
                                 new ConsoleTraceListener(false));
    loggerFactory.AddTraceSource(sourceSwitch, 
                                 new EventLogTraceListener("Application"));
}

Any ideas on what am I doing wrong?

Answer 1

If you look at your web.config, it probably has stdoutLogEnabled="false". If you set that to true, then anything that is written to standard output will be written to a file. And the stdoutLogFile determines where it goes, which by default is under d:\home\logfiles.

Now you need to make sure that your logging actually goes to stdout. Doing Console.WriteLine would definitely work. I think it's probably possible to also configure things via ILoggerFactory in your startup.cs to make logs go to stdout.

Answer 2

I've found an simple trick for azure app ,see https://github.com/aspnet/Logging/tree/dev/src/Microsoft.Extensions.Logging.AzureAppServices, please add the package "Microsoft.Extensions.Logging.AzureAppServices": "1.0.0-preview1-final" and update related dependencies, add the azure diagnostics in startup.cs like this :

loggerFactory.AddConsole(Configuration.GetSection("Logging"));
loggerFactory.AddDebug();
loggerFactory.AddAzureWebAppDiagnostics(); // for default setting.

or for custom setting:

loggerFactory.AddAzureWebAppDiagnostics(new AzureAppServicesDiagnosticsSettings( ...)); // add custom setting.
// see here for detailed member properties: https://github.com/aspnet/Logging/blob/dev/src/Microsoft.Extensions.Logging.AzureAppServices/AzureAppServicesDiagnosticsSettings.cs

And enable the diagnostics log on azure, both logging on blob and file are work well. No need for any extra configuration. :)