Question

What are the better ways to achieve low overhead distributed logging on Azure?

Answer 1

We use log4net as the logging library for our multi-tennant Azure Web Role. The log4net ADO.Net appender is used to log all errors to a SQL Azure database. To filter logs by client/user, we use a few log4net.GlobalContext properties, like so:

log4net.GlobalContext.Properties["Domain"] = new Log4netDomainProvider();
log4net.GlobalContext.Properties["Username"] = new Log4netUsernameProvider();

Each “Provider” is just a simple class that overrides the ToString() method. When ToString() is called by log4net, we grab a value from the current session (this technique is discussed in this SO answer).

public class Log4netDomainProvider
{
    public override string ToString()
    {
        string retval = null;

        if (HttpContext.Current == null)
            retval = "HttpContext is null";
        else if (HttpContext.Current.Session == null)
            retval = "HttpContext.Current.Session is null";
        else
            retval = HttpContext.Current.Session["Domain"];

        return retval;
    }
}

I hope this addresses your question. If so, you might want to check out this good write-up on log4net logging contexts.