定义Azure Web角色的扩展阈值

Question

Azure embraces the notion of elastic scaling and I've been able to acheive this with my Worker Roles . However, when it comes to my Web Roles ( eg MVC Apps ) I am not sure what to monitor ( or how ) to determine when its a good time to increase ( or descrease ) the number of running instances. I'm assuming I need to monitor one or many Performance Counters but not sure where to start.

Can anyone recommend a best practice for assessing an MVC Web Role instances load relative to scaling decisions?

Answer 1

This question is a bit open-ended, as monitoring is typically app-specific. Having said that:

Start with simple measurements that you'd look at on a local server, representing KPIs for your app. For instance: Maybe look at network utilization. This TechNet article describes performance counters collected by System Center for Windows Azure. For instance:

• ASP.NET Applications Requests/sec
• Network Interface Bytes
• Received/sec
• Network Interface Bytes Sent/sec
• Processor % Processor Time Total
• LogicalDisk Free Megabytes
• LogicalDisk % Free Space
• Memory Available Megabytes

You may also want to watch # of requests queued and request wait time.

Network utilization is interesting, since your NIC provides approx. 100Mbps per core and could end up being a bottleneck even when CPU and other resources are underutilized. You may need to scale out to more instances to handle high-bandwidth scenarios.

Also: I tend to give less importance to CPU utilization, even though it's so easy to measure (and shows up so frequently in examples). Running a CPU at near capacity is a good thing usually, since you're paying for it and might as well use as much as possible.

As far as decreasing : This needs to be handled a bit more carefully. Windows Azure compute is billed by the hour. If, say, you scale out to an extra instance at 11:50 and scale in again at 12:10, you've just incurred two cpu-hours. Also: You don't want to scale out, then take new measurements and deciding you can now scale back again (effectively creating a constant pulse of adding and decreasing instances). To make things easier, consider the Autoscaling Application Block (WASABi), found in the Enterprise Library . This has all the scale rules baked in (such as the ones I just mentioned) and is very straightforward to use.