Is Your Application a Good Fit for Windows Azure?

Before you can determine if your application is well-suited for Windows Azure, you must first understand some of the main benefits of the platform. A complete list of benefits can be found in the Windows Azure documentation and many articles and videos about Windows Azure. One excellent paper on this subject is Cloud Optimization – Expanding Capabilities, while Aligning Computing and Business Needs.

There are several benefits to having hardware and infrastructure resources managed for you. Let's look at a few of these benefits at a high level before we discuss scenarios that take advantage of these features.

When you deploy your application and services to the cloud, Windows Azure provides the necessary virtual machines, network bandwidth, and other infrastructure resources. If machines go down for hardware updates or due to unexpected failures, new virtual machines are automatically located for your application.

Because you only pay for what you use, you can start off with a smaller investment rather than incurring the typical upfront costs required for an on-premises deployment. This can be especially useful for small companies. In an on-premises scenario, these organizations might not have the data center space, IT skills, or hardware skills necessary to successfully deploy their applications. The automatic infrastructure services provided by Windows Azure offer a low barrier of entry for application deployment and management.

Dynamic scaling refers to the capability to both scale out and scale back your application depending on resource requirements. This is also referred to as elastic scale. Before describing how this works, you should understand the basic architecture of a Windows Azure application. In Windows Azure, you create roles that work together to implement your application logic. For example, one web role could host the ASP.NET front-end of your application, and one or more worker roles could perform necessary background tasks. Each role is hosted on one or more virtual machines, called role instances, in the Windows Azure data center. Requests are load balanced across these instances. For more information about roles, see the paper The Windows Azure Programming Model.

If resource demands increase, new role instances running your application code can be provisioned to handle the load. When demand decreases, these instances can be removed so that you don't have to pay for unnecessary computing power. This is much different from an on-premises deployment where hardware must be over-provisioned to anticipate peak demands. This scaling does not happen automatically, but it is easily achieved through either the web portal or the Service Management API. The paper Dynamically Scaling an Application demonstrates one way to automatically scale Windows Azure applications. There is also an Autoscaling Application Block created by the Microsoft Patterns and Practices team.

If your application requires fluctuating or unpredictable demands for computing resources, Windows Azure allows you to easily adjust your resource utilization to match the load.

Windows Azure provides a platform for highly available applications that can reliably store and access backend data through storage services or Windows Azure SQL Database.

First Windows Azure ensures high availability of your compute resources when you have multiple instances of each role. Role instances are automatically monitored, so it is able to respond quickly to hardware restarts or failures by automatically deploying a role to a new instance.

Second, Windows Azure ensures high availability and durability for data stored through one of the storage services. Windows Azure storage services replicate all data to at least three different servers. Similarly, SQL Database replicates all data to guarantee availability and durability.

Other Windows Azure services provide similar high availability guarantees. For more information, see the Windows Azure SLA.

With an understanding of the strengths of the Windows Azure platform, you can begin to look at the scenarios that are best suited for the cloud. The following sections discuss several of these patterns and how Windows Azure is ideally suited for certain workloads and goals. The video Windows Azure Design Patterns explains many of the scenarios below and provides a good overview of the Windows Azure platform.

Tip
Although there is a focus on application scenarios here, understand that you can choose to use individual services of Windows Azure. For example, if you find that using blob storage solves an application problem, it is possible that the rest of your application remains outside of the Cloud. This is called a hybrid application and is discussed later in this topic.

Highly Available Services

Periodic Workloads

Another good fit for Windows Azure is some form of an "on and off" workload. Some applications do not need to run continuously. One simple example of this is a demo or utility application that you want to make available only for several days or weeks. Windows Azure allows you to easily create, deploy, and share that application with the world. But once its purpose is accomplished, you can remove the application and you are only charged for the time it was deployed.

Note
Note: You must remove the deployment, not just suspend the application, to avoid charges for compute time.

Also consider a large company that runs complex data analysis of sales numbers at the end of each month. Although processing-intensive, the total time required to complete the analysis is at most two days. In an on-premises scenario, the servers required for this work would be underutilized for the majority of the month. In Windows Azure, the business would only pay for the time that the analysis application is running in the cloud. And assuming the architecture of the application is designed for parallel processing, the scale out features of Windows Azure could enable the company to create large numbers of worker role instances to complete more complex work in less time. In this example, you should use code or scripting to automatically deploy the application at the appropriate time each month.

Unpredictable Growth

Workload Spikes

Infrastructure Offloading

Not all applications should be moved to the cloud. Only applications that benefit from Windows Azure features should be moved to the cloud.

A good example of this would be a personal blog website intended for friends and family. A site like this might contain articles and photographs. Although you could use Windows Azure for this project, there are several reasons why Windows Azure is not the best choice. First, even though the site might only receive a few hits a day, one role instance would have to be continuously running to handles those few requests (note that two instances would be required to achieve the Windows Azure SLA for compute). In Windows Azure, the cost is based on the amount of time that each role instance has been deployed (this is known in Windows Azure nomenclature as compute time); suspending an application does not suspend the consumption of (and charge for) compute time. Even if this site responded to only one hit during the day, it would still be charged for 24 hours of compute time. In a sense, this is rented space on the virtual machine that is running your code. So, at the time of writing this topic, even one extra small instance of a web role would cost $30 a month. And if 20 GB of pictures were stored in blob storage, that storage plus transactions and bandwidth could add another $6 to the cost. The monthly cost of hosting this type of site on Windows Azure is higher than the cost of a simple web hosting solution from a third party. Most importantly, this type of web site does not require resource management, dynamic scaling, high availability, and durability.

Windows Azure allows you to choose only the options that are suited to your business’ needs. For example, you might find instances in which certain data cannot be hosted in the cloud for legal or regulatory reasons. In these cases, you might consider a hybrid solution, where only certain data or specific parts of your application that are not as sensitive and need to be highly available are hosted in Windows Azure.

There are other scenarios that are not well-suited to Windows Azure. By understanding the strengths of Windows Azure, you can recognize applications or parts of an application that will not leverage these strengths. You can then more successfully develop the overall solution that most effectively utilizes Windows Azure capabilities.

Of course, evaluating a move to Windows Azure involves more than just knowing that your application or business goals are well-suited for the cloud. It is also important to evaluate architectural and development characteristics of your existing or new application. A quick way to start this analysis is to use the Microsoft Assessment Tool (MAT) for Windows Azure. This tool asks questions to determine the types of issues you might have in moving to Windows Azure. Next to each question is a link called "See full consideration", which provides additional information about that specific area in Windows Azure. These questions and the additional information can help to identify potential changes to the design of your existing or new application in the cloud.

In addition to the MAT tool, you should have a solid understanding of the basics of the Windows Azure platform. This includes an understanding of common design patterns for the platform. Start by reviewing the Windows Azure videos or reading some of the introductory white papers, such as The Windows Azure Programming Model. Then review the different services available in Windows Azure and consider how they could factor into your solution. For an overview of the Windows Azure services, see the MSDN documentation.

It is beyond the scope of this paper to cover all of the possible considerations and mitigations for Windows Azure solutions. However, the following table lists four common design considerations along with links to additional resources.

Beyond these issues, you can learn a lot about potential development challenges and solutions by reviewing content on migrating applications to Windows Azure. The Patterns and Practices group at Microsoft published the following guidance on migration: Moving Applications to the Cloud on the Microsoft Windows Azure Platform. You can find additional resources on migration from the Windows Azure web site: Migrate Services and Data.

Windows Azure offers a platform for creating and managing highly scalable and available services. You pay only for the resources that you require and then scale them up and down at any time. And you don't have to own the hardware or supporting infrastructure to do this. If your business can leverage the platform to increase agility, lower costs, or lower risk, then Windows Azure is a good fit for your application. After making this determination, you can then look at specific architecture and development options for using the platform. This includes decisions about new development, migration, or hybrid scenarios. At the end of this analysis, you should have the necessary information to make an informed decision about how to most effectively use Windows Azure to reach your business goals.