Windows Azure compute

Windows Azure compute service enables developers to run any applications starting from .NET, Java, PHP etc… Developers now have the ability to choose the size of VMs to run their application based on the applications resource requirements. Windows Azure compute instances come in four unique sizes to enable complex applications and workloads.                   

Compute Instance Size	CPU	Memory	Instance Storage	I/O Performance
Small	1.6 GHz	1.75 GB	225 GB	Moderate
Medium	2 x 1.6 GHz	3.5 GB	490 GB	High
Large	4 x 1.6 GHz	7 GB	1,000 GB	High
Extra large	8 x 1.6 GHz	14 GB	2,040 GB	High

In Windows Azure for an application to scale out, it will run multiple copy of the code in various virtual machines.  Windows Azure application consists of Web role instances and/or Worker role instances, each of which runs in its own Windows virtual machine.

Web role instance nothing but which accepts a HTTP/HTTPS request and respond back to customer web request via IIS 7 (ASP.NET Application). This instance needs to run in an IIS 7 Web Server only.

Worker role instance will do some background job (similar to Windows Service) and doesn’t expose to outside world directly. For instance one can use Worker role process to do some parallel bulk computing operations and then share with web role instance. A worker role can have any number of HTTP, HTTPS, or TCP endpoints.

Windows Azure services may be comprised of one or both types of roles and can run multiple instances of each type. Web / Worker Role instances can be added or removed based on demand and allow applications to quickly and economically scale-up or down as per the need. Windows Azure also exposes set of API’s to programmatically control the role instances.