Azure web site questions

Question

I currently have a web application deployed to "Web Sites" - This is configured in standard mode and it performs really well from what I have seen so far.

I have a few questions:

1)My instance size is currently small - however I can scale out to 10 instances. Does this also mean that if I change my instance size to medium or large, I can still have 10 instances?

2)What is the maximum number of instances I can have for an azure web site?

3)Is there any SLA for a single azure instance?

4)Is it possible to change the instance size programatically or is better to just change the instance count

Answer 1

1. Yes, the default limit is 10 instances regardless of the size.

2. The default limit is 10 instances, but you can contact Azure Support to have the limit increased. Default and "real" limits for Azure services are documented here.

3. According to the Websites pricing page Free and Shared sites have no SLA and Basic and Standard sites have 99.9% uptime SLA. Having a single instance means that during the 0.1% outage time (43.8 minutes per month) your site will be down. If you have multiple instances then most likely at least one will be up at any given time.

4. Typically instance auto-scaling is used to handle variation in demand while instance size would be used for application performance. If you only get 100 requests per day but each request is slow because it's maxing out CPU then adding more instances won't help you. Likewise if you're getting millions of requests that are being processed quickly but the volume is maxing out your resources then adding more instances is probably the better solution.

Answer 2

1) Yes

2) 10 for standard.

3) Yes, for Websites Basic and Standard, MS guarantee a 99.9% monthly availability.

4) It depends on a lot of factors. The real question is "Is it better for your app to scale up or scale out?"