I work on Windows Azure billing at Microsoft. I guess you can blame me for what shows up on your bill (really, go for it: baslam at microsoft dot com, I'd love to hear from you). I want to use this blog post to briefly explain how Windows Azure billing works, and hopefully take some mystery out of what can seem like an opaque process.
Your bill's journey starts with you signing up for Windows Azure. If you haven't signed up, go visit our beautiful new site at windowsazure.com and give it a shot. Sign-up for Azure used to be like pulling teeth, but as of Dec. 10, 2011, it is a three-step wizard with a free 3-month trial (really, it's free).
If you click on this link and de-construct the follow-up link, you will see something interesting:
This Windows Live login link contain an offer ID. When you complete signup, you end up purchasing an offer. Specifically, you are purchasing MS-AZR-0018P, which is the Introductory 3-month Special offer.
Why is this important? An offer simply describes the price you will be charged for various resources and the _included quantities _you will receive. For example, MS-AZR-0018P gives you a certain rate at which you will be charged for compute, storage etc. and gives you a certain number of compute hours, storage, etc. Offers are actually _very _interesting - certain offers (like MSDN and Intro Special) have magical properties, such as one that prevents you from being charged until you specifically want to be charged.
Why are there are different offers? You guessed it - because Windows Azure has many different types of customers. MSDN subscribers, for example, get an awesome package. So do Enterprise Agreement customers (i.e. companies that sign large deals with Microsoft). You can see all the offers here and here.
Once you purchase an offer, it creates an instance of a Subscription.
A subscription is a living instance of an offer. It remembers what offer you purchased, and is the basic unit of billing in Windows Azure. In my account, for example, I have two subscriptions. It is interesting to note that all resources in the Windows Azure Management Portal have to be tied to exactly one subscription.
2. The journey begins..
Now you have signed up and purchased a subscription. Once you start using a resource, that resource starts emitting what are called usage meters. These meters snake their way down from the resource to the commerce engine, where they are rolled up, and saved off. For example, let's say you spin up a VM and run it for 4 hours. The VM resource will emit meters (let's say every hour), telling the Azure commerce engine that you (or, specifically, your Windows Live ID) has consumed a certain amount of resources. The same goes for storage, bandwidth, etc.
All of these meters will eventually add up to your bill.
3. And you end up with a bill...
Bills for Windows Azure are generated on your account anniversary date (i.e. the date of the month when you created your account). You will get an email and when you log into account.windowsazure.com, you will see your bill. Your bill is just a roll-up of your usage over the month.
Do you have any questions about Windows Azure billing? I'll be happy to answer them here!