Windows Azure is the paradigm for the platform-as-a-Service (PaaS) model for cloud services. It provides a high-level, service-hosting environment into which services can be inserted. The hosting environment is modeled on services, roles, and instances.
Only two role types are available prior to Windows Azure SDK v1.3: web roles and worker roles. The primary difference between them is that web roles are designed to host web applications in IIS whereas worker roles are for other types of applications. However, both roles share the same restrictions on the software that can be installed on them.
The Windows Azure SDK v1.3 release added support for a new role type, VM role. This role allows a Guest OS image to be uploaded into a hosted service. The image can have any desired software installed on it prior to upload. However, it is important to remember that VM roles are still stateless and any changes made to instances after they are deployed will not survive an instance failure...