windows azure automatic scaling

Question

Hi I have a web app deployed as a Cloud Service on Windows Azure. Now I am performing some load/stress test against this app. In the Azure Management Portal I have configured the web role to scale automatically when the CPU goes over 40%.

I start the tests with only one instance of this web role. As the test progresses, I have set the number of concurrent users to increase over time up to 2000 users.

After I start the test, I connect via remote desktop to the web role instance on Azure and I monitor the CPU usage. After 10 mins or so, the CPU is constantly at 100% (and in fact my requests in the test take a very long time to complete) but if I check the CPU of the very same web role on the Azure management portal it says 1, 2 or 6, there was a peak of 70% but it sunk back immediately (but never the values I see in its task manager when I am connected in remote desktop) or even does not display any value (I go to the dashboard page of my cloud service), which means the graph is not updated any more.

Furthermore, and this is the point of my question, NO SCALING of the web role instances is performed whatsoever.

Any ideas where/what I am missing? Feel free to ask if my explanation is incomplete.

Answer 1

Autoscaling on the CPU metric for a Cloud Service or Virtual Machine doesn't occur as fast as you are expecting (~10+ minutes). In this scenario, the CPU metric is averaged across all instances of the services for a period of 1 hour. Therefore, your autoscaling actions will not be immediate.

You can read more about this and some recommendations for configuring your autoscale settings here .

If you want to tighten this up a little more then take a look at this post where I show how to set the TimeWindow using the Monitoring Service Management Library. You may be able to get closer to what you want taking this approach.

Answer 2

A few things to consider:

1) As Rick pointed out, by default CPU is taken at an hour average

2) If you start at only 1 server, and then autoscale up to 2, your first server will get yanked out of load balancer during the scale operation. You should really always have a minimum of 2 servers at all time.

3) Feel free to check out AzureWatch (link in my profile).. it was designed to perform decently advanced scaling scenarios and allows you to configure scaling rules without touching APIs