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When I run a worker role instance on Azure, is it a complete VM running in a shared host (like EC2)? Or is it running in a shared system (like Heroku)?
For example, what happens if my application starts requesting 100 GB of memory? Will it get killed off automatically for violation of limits (á la Google App Engine), or will it just exhaust the VM, so that the Azure fabric restarts it?
Do two roles ever run in the same system?
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There are two types of Azure Cloud Services roles. The only difference between the two is how your role is hosted on the VMs: Web role: Automatically deploys and hosts your app through IIS. Worker role: Does not use IIS, and runs your app standalone.
Define role instance in Azure. A role instance is nothing but a virtual machine where the application code runs with the help of running role configurations. There can also be multiple instances of a role as per the definition in the cloud service configuration files.
The Windows Azure VM role lets you run a virtual hard disk image, store that image in the cloud and load and run it on demand. You understand benefits of cloud computing, the efficiencies to be gained, the ability to scale your infrastructure based on immediate need and make more strategic use of IT staff.
Account Administrator, Service Administrator, and Co-Administrator are the three classic subscription administrator roles in Azure.
It's a whole VM, and the resources allocated are based directly on the size of VM you choose, from 1.75GB (Small) to 14GB (XL), with 1-8 cores. There's also an Extra Small instance with 768MB RAM and shared core. Full VM size details are here.
With Windows Azure, your VM is allocated on a physical server, and it's the fabric's responsibility of finding such servers to properly allocate all of your web or worker role instances. If you have multiple instances, this means allocating these VMs across fault domains.
With your VM, you don't have to worry about being killed off if you try allocating too much in the resource dep't: it's just like having a machine, and you can't go beyond what's there.
As far as two roles running on the same system: Each role has instances, and with multiple instances, as I mentioned above, your instances are divided into fault domains. If, say, you had 4 instances and 2 fault domains, it's possible that you may have two instances on the same rack (or maybe same server).
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