Cloudware Vendor Solutions - Guide to Cloud Computing for Business and Technology Managers - page 338

can be used to store large objects containing text or binary data. Based on
this service, Windows Azure Drive allows to format a binary data object to
be used as an NTFS volume. A queue service ensures a reliable data exchange
between the components. Finally, the virtual network service constitutes the
basis for a transparent communication between local and remote resources. It
can be used to integrate Windows Azure services into a local Active Directory.
In addition, the platform includes the Windows Azure AppFabric that uses
secure connectivity to bridge traditional IT systems to cloud applications.
With the Azure service platform, software products can be installed as cloud
services on the Internet or alternatively as applications in the in-house data
center. The two methods can also be combined to implement a flexibly scal-
able hybrid cloud. For this purpose, Web and business developers have the
choice of a variety of established tools, such as Microsoft.NET, Visual Studio,
or many other products that are available as commercial or open-source
software. Applications can be developed and tested locally before they are
finally uploaded and published to the Azure cloud.
Scaling, load balancing, memory management, and reliability are ensured
by a fabric controller, a distributed application replicated across a group
of machines that owns all of the resources in its environment—computers,
switches, load balancers—and it is aware of every Windows Azure
application.
The fabric controller decides where new applications should run; it chooses
the physical servers to optimize utilization using configuration information
uploaded with each Windows Azure application. The configuration infor-
mation is an XML-based description of how many Web role instances, how
many worker role instances, and what other resources the application needs.
The fabric controller uses this configuration file to determine how many
VMs to create.
Blobs, tables, queues, and drives are used as scalable storage. A blob con-
tains binary data; a container consists of one or more blobs. Blobs can be
up to a terabyte, and they may have associated metadata (e.g., the informa-
tion about where a JPEG photograph was taken). Blobs allow a Windows
Azure role instance to interact with persistent storage as though it were a
local NTFS6 file system. Queues enable Web role instances to communicate
asynchronously with worker role instances.
The Content Delivery Network (CDN) maintains cache copies of data to
speed up computations. The connect subsystem supports IP connections
between the users and their applications running on Windows Azure. The
API to Windows Azure is built on REST, HTTP, and XML. The platform
includes five services: Live Services, SQL Azure, AppFabric, SharePoint,
and Dynamics CRM. A client library and tools are also provided for devel-
oping cloud applications in Visual Studio.
The computations carried out by an application are implemented as one
or more roles; an application typically runs multiple instances of a role. For
the use of Windows Azure services, three different roles have been defined: