How can I view console or trace output in an azure app service? Console.WriteLine or Trace.TraceError

I finally figured it out myself. I needed to add configuring AzureFileLoggerOptions. Without those options, nothing showed up in the Azure output.

.ConfigureLogging(logging => logging.AddAzureWebAppDiagnostics())
.ConfigureServices(serviceCollection => serviceCollection
    .Configure<AzureFileLoggerOptions>(options =>
    {
        options.FileName = "azure-diagnostics-";
        options.FileSizeLimit = 50 * 1024;
        options.RetainedFileCountLimit = 5;
    }).Configure<AzureBlobLoggerOptions>(options =>
    {
        options.BlobName = "log.txt";
    })
)

In summary, for .Net Core 3.1, to get your messages to show up in the "Log Stream", you need to enable "Application Logging" in the "App Service Logs" section of Azure. In your code you need to reference:

using Microsoft.Extensions.DependencyInjection;

using Microsoft.Extensions.Logging.AzureAppServices;

Also, in my case, I am using Blazor/SignalR and don't have an MVC Controller, so I couldn't figure out how to access the Logging framework in my class. I am sure there is a better way, but by exposing the ILogger as in the code below I was able to reference it from anywhere within my code base.

I have a static method I call to write to the log (console when I am actively debugging on my pc, or Azure "Log Stream" when running in Azure:

public static void WriteToLog(string message)
{
    Program.Logger.LogError(message);
}

Code in my Program.cs looks like this:

public class Program
    {
        public static ILogger Logger;
        public static void Main(string[] args)
        {
            //CreateHostBuilder(args).Build().Run();

            var host = CreateHostBuilder(args).Build();

            var LoggerF = LoggerFactory.Create(builder =>
            {
                builder.AddFilter("BlazorDiceRoller", LogLevel.Warning)
                .AddConsole().AddAzureWebAppDiagnostics()
                .AddFilter("Microsoft", LogLevel.Warning)
                .AddFilter("System", LogLevel.Warning);
            });
            Logger = LoggerF.CreateLogger<Program>();
            host.Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
            .ConfigureLogging(logging => logging.AddAzureWebAppDiagnostics())
            .ConfigureServices(serviceCollection => serviceCollection
                .Configure<AzureFileLoggerOptions>(options =>
                {
                    options.FileName = "azure-diagnostics-";
                    options.FileSizeLimit = 50 * 1024;
                    options.RetainedFileCountLimit = 5;
                }).Configure<AzureBlobLoggerOptions>(options =>
                {
                    options.BlobName = "log.txt";
                })
            )
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
    }