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

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).