Cloud Services with Windows Azure : Windows Azure Platform Overview

• Windows Azure (application container)

• Microsoft SQL Azure

• Windows Azure platform AppFabric
  

The Windows Azure platform is part of the Microsoft cloud, which consists of multiple categories of services:

• cloud-based applications– These are services that are always available and highly scalable. They run in the Microsoft cloud that consumers can directly utilize. Examples include Bing, Windows Live Hotmail, Office Live, etc.

• software services– These services are hosted instances of Microsoft’s enterprise server products that consumers can use directly. Examples include Exchange Online, SharePoint Online, Office Communications Online, etc.

• platform services– This is where the Windows Azure platform itself is positioned. It serves as an application platform public cloud that developers can use to deploy next-generation, Internet-scale, and always available solutions.

• infrastructure services– There is a limited set of elements of the Windows Azure platform that can support cloud-based infrastructure resources.

Figure 1 illustrates the service categories related to the Windows Azure platform. Given that Windows Azure is itself a platform, let’s explore it as an implementation of the PaaS delivery model.

Figure 1. A high-level representation of categories of services available in the Windows Azure cloud.

The Windows Azure platform was built from the ground up using Microsoft technologies, such as the Windows Server Hyper-V-based system virtualization layer. However, the Windows Azure platform is not intended to be just another off-premise Windows Server hosting environment. It has a cloud fabric layer, called the Windows Azure Fabric Controller, built on top of its underlying infrastructure.

The Windows Azure Fabric Controller pools an array of virtualized Windows Server instances into a logical entity and automatically manages the following:

• resources

• load balancing

• fault-tolerance

• geo-replication

• application lifecycle

These are managed without requiring the hosted applications to explicitly deal with the details. The fabric layer provides a parallel management system that abstracts the complexities in the infrastructure and presents a cloud environment that is inherently elastic. As a form of PaaS, it also supports the access points for user and application interactions with the Windows Azure platform.

The Windows Azure platform essentially provides a set of cloud-based services that are symmetric with existing mainstream on-site enterprise application platforms (Figure 2).

Figure 2. An overview of common Windows Azure platform capabilities.

For example:

• storage services – a scalable distributed data storage system that supports many types of storage models, including hash map or table-like structured data, large binary files, asynchronous messaging queues, traditional file systems, and content distribution networks

• compute services – application containers that support existing mainstream development technologies and frameworks, including .NET, Java, PHP, Python, Ruby on Rails, and native code.

• data services – highly reliable and scalable relational database services that also support integration and data synchronization capabilities with existing on-premise relational databases

• connectivity services – these are provided via a cloud-based service bus that can be used as a message intermediary to broker connections with other cloud-based services and services behind firewalls within on-premise enterprise environments

• security services – policy-driven access control services that are federation-aware and can seamlessly integrate with existing on-premise identity management systems

• framework services – components and tools that support specific aspects and requirements of solution frameworks

• application services – higher-level services that can be used to support application development, such as application and data marketplaces

All of these capabilities can be utilized individually or in combination.

Windows Azure (Application Container)

Windows Azure serves as the development, service hosting, and service management environment. It provides the application container into which code and logic, such as Visual Studio projects, can be deployed. The application environment is similar to existing Windows Server environments. In fact, most .NET projects can be deployed directly without significant changes.

A Windows Azure instance represents a unit of deployment, and is mapped to specific virtual machines with a range of variable sizes. Physical provisioning of the Windows Azure instances is handled by the cloud fabric. We are required only to specify, by policy, how many instances we want the cloud fabric to deploy for a given service.

We have the ability to manually start and shut down instances, and grow or shrink the deployment pool; however, the cloud fabric also provides automated management of the health and lifecycles of instances. For example, in the event of an instance failure, the cloud fabric would automatically shut down the instance and attempt to bring it back up on another node.

Windows Azure also provides a set of storage services that consumers can use to store and manage persistent and transient data. Storage services support geo-location and offer high durability of data by triple-replicating everything within a cluster and across data centers. Furthermore, they can manage scalability requirements by automatically partitioning and load balancing services across servers.

Also supported by Windows Azure is a VHD-based deployment model as an option to enable some IaaS requirements. This is primarily geared for services that require closer integration with the Windows Server OS. This option provides more control over the service hosting environment and can better support legacy applications.

SQL Azure

SQL Azure is a cloud-based relational database service built on SQL Server technologies that exposes a fault-tolerant, scalable, and multi-tenant database service. SQL Azure does not exist as hosted instances of SQL Server. It also uses a cloud fabric layer to abstract and encapsulate the underlying technologies required for provisioning, server administration, patching, health monitoring, and lifecycle management. We are only required to deal with logical administration tasks, such as schema creation and maintenance, query optimization, and security management.

A SQL Azure database instance is actually implemented as three replicas on top of a shared SQL Server infrastructure managed by the cloud fabric. This cloud fabric delivers high availability, reliability, and scalability with automated and transparent replication and failover. It further supports load-balancing of consumer requests and the synchronization of concurrent, incremental changes across the replicas. The cloud fabric also handles concurrency conflict resolutions when performing bi-directional data synchronization between replicas by using built-in policies (such as last-writer-wins) or custom policies.

Windows Azure Platform AppFabric

This represents the version of AppFabric that is local to the Windows Server environment. Windows Azure platform AppFabric (with the word “platform” intentionally not capitalized), is the cloud-based version of AppFabric that runs on Windows Azure.

Windows Azure platform AppFabric helps connect services within or across clouds and enterprises. It provides a Service Bus for connectivity across networks and organizational boundaries, and an Access Control service for federated authorization as a service.

The Service Bus acts as a centralized message broker in the cloud to relay messages between services and service consumers. It has the ability to connect to on-premise services through firewalls, NATs, and over any network topology.

Its features include:

• connectivity using standard protocols and standard WCF bindings

• multiple communication models (such as publish-and-subscribe, one-way messaging, unicast and multicast datagram distribution, full-duplex bi-directional connection-oriented sessions, peer-to-peer sessions, and end-to-end NAT traversal)

• service endpoints that are published and discovered via Internet-accessible URLs

• global hierarchical namespaces that are DNS and transport-independent

• built-in intrusion detection and protection against denial-of-service attacks

Access Control acts as a centralized cloud-based security gateway that regulates access to cloud-based services and Service Bus communications, while integrating with standards-based identity providers (including enterprise directories such as Active Directory and online identity systems like Windows Live ID).