Azure diagnostics and Class onStop (on scale down) - How to prevent log loss?

Question

I am initializing my Azure Diagnostics inside onStart of my Web Role, and have it scheduled to transfer logs every 5 minutes. But when the auto-scale shuts down one my roles we are loosing the logs since the last transfer. What can I do in onStop to prevent this from happening? Is there a way to force the log transfer and prevent onStop from finishing until it's done? Thanks!

Answer 1

Just have your log transfer in the onStop method. Or alternatively, if that's done in a thread, use a flag and a loop in the onStop method to sleep until the flag is set.

SaveLogAsync();
while(!saved)
{
    Thread.Sleep(100);
}

There is still a max amount of time the onStop method will run for before it's forced to shut down. I think it's 5 minutes.

Answer 2

To transfer diagnostics data when role is shutting down, you would need to perform an operation called On-Demand Transfer. This will start transferring the data stored in buffer to diagnostics storage account. You may find this link helpful in performing On-Demand Transfer: http://msdn.microsoft.com/en-us/library/windowsazure/gg433075.aspx.

And David is correct. You get about 5 minutes to perform this operation. See this link for more details: http://msdn.microsoft.com/en-us/library/microsoft.windowsazure.serviceruntime.roleentrypoint.onstop.aspx. To handle OnStop event gracefully, you may find this blog post useful: http://blogs.msdn.com/b/windowsazure/archive/2013/01/14/the-right-way-to-handle-azure-onstop-events.aspx.