How do I need to log to see my logs in App Service logs

Question

I have enabled logging to Application logging to both FileSystem and Blob. I log messages using ILogger<T>.LogInformation() and Trace.WriteLine(). None of those are visible in blob. I also cannot find them on filesystem. I also can't see them when I enable log streaming.

Do I need to configure something in my ASP.NET Core application?

Answer 1

Here is a simple way(the referred article is here):

I tested it with .NET core 2.2 mvc project.

The necessary nuget package:

Microsoft.Extensions.Logging.AzureAppServices, version 2.2.0

1.In Startup.cs -> ConfigureServices method, add this line of code:

services.AddSingleton<ILoggerFactory>(new LoggerFactory());

In Startup.cs -> Configure method, change it looks like below:

       public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            //add the following code here
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            loggerFactory.AddAzureWebAppDiagnostics(
                new AzureAppServicesDiagnosticsSettings
                {
                    OutputTemplate = "{Timestamp:yyyy-MM-dd HH:mm:ss zzz} [{Level}] {RequestId}-{SourceContext}: {Message}{NewLine}{Exception}"
                }
                );

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }

then add following code in the HomeController.cs:

        private readonly ILogger _logger;
        public HomeController(ILoggerFactory loggerFactory)
        {
            _logger = loggerFactory.CreateLogger<HomeController>();
        }

        public IActionResult Index()
        {
            _logger.LogInformation("This is a Log information!!!");
            _logger.LogError("This is a Logger error!!!");
            return View();
        }

2.After publish to azure, in azure portal -> the web app -> App service logs, set the blob storage. The screenshot as below:

3.Run the web, and check the logs in the specified blob storage:

Answer 2

The [Microsoft.Extensions.Logging.AzureAppServices][1] provider package writes logs to text files in an Azure App Service app's file system and to blob storage in an Azure Storage account.

The provider package isn't included in the shared framework. To use the provider, add the provider package to the project.

To configure provider settings, use AzureFileLoggerOptions and AzureBlobLoggerOptions, as shown in the following example:

public static void Main(string[] args)
{
    var host = CreateHostBuilder(args).Build();

    var todoRepository = host.Services.GetRequiredService<ITodoRepository>();
    todoRepository.Add(new Core.Model.TodoItem() { Name = "Feed the dog" });
    todoRepository.Add(new Core.Model.TodoItem() { Name = "Walk the dog" });

    var logger = host.Services.GetRequiredService<ILogger<Program>>();
    logger.LogInformation("Seeded the database.");

    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>();
        });

You can refer below link for additional reference:

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-3.1#azure-app-service-provider

Hope it helps.