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

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 got Streaming Log output working for an ASP.NET 5 web app by writing the following class (based on David Ebbo's example):

public class AzureApplicationLogTraceListener : TraceListener
{
    private readonly string _logPath;
    private readonly object _lock = new object();

    public AzureApplicationLogTraceListener()
    {
        string instanceId = Environment.GetEnvironmentVariable("WEBSITE_INSTANCE_ID");
        if (instanceId != null)
        {
            string logFolder = Environment.ExpandEnvironmentVariables(@"%HOME%\LogFiles\application");
            Directory.CreateDirectory(logFolder);
            instanceId = instanceId.Substring(0, 6);
            _logPath = Path.Combine(logFolder, $"logs_{instanceId}.txt");

        }
    }

    public override void Write(string message)
    {
        if (_logPath != null)
        {
            lock (this)
            {
                File.AppendAllText(_logPath, message);
            }
        }
    }

    public override void WriteLine(string message)
    {
        Write(message + Environment.NewLine);
    }
}

and then putting this in my Startup.Configure:

Trace.Listeners.Add(new AzureApplicationLogTraceListener());

This only supports filesystem-based logging (which is sufficient for live log streams).

Answer 3

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. :)