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      The reality is with a multiple-application instances model, the level of application availability is higher than when using a reliable infrastructure model. Although the reliable infrastructure provides zero downtime from planned maintenance operations (as does the best-effort infrastructure with multiple instances of the application on different fault domains), a reliable infrastructure cannot protect from downtime in an unplanned failure. If a host fails, the cluster infrastructure in the reliable model will restart the VM on another node. That restart takes time, and the OS and/or application may need integrity checks and possibly recovery actions because essentially the OS inside the VM was just powered off. In the best-effort infrastructure using multiple instances of the application, unplanned failure is covered without risk of corruption, as the other instance would still be running. Additionally, though the reliable infrastructure protects against host failure, it cannot provide protection if the OS inside a VM hangs or errors in some way that is not seen as a problem for the host environment. In such a case, no corrective action is taken, and the service is left unavailable. Using an application-aware approach, any issues in the application could be detected, and clients would be sent to the other instance until any problems were resolved.

      Getting Access to Microsoft Azure

      For a typical on-premises solution, there are many hurdles to the access and adoption of a new technology. You need hardware to run the solution and somewhere to store that hardware, and you have to obtain and deploy the various operating system requirements and applications. With public cloud solutions, the services are sitting out there, just waiting for you to start using them. Primarily, that means a way to pay for the services. If, however, you want to just try Azure, you don’t even need that.

      Free Azure Trials and Pay-as-You-Go

      The first way to gain access to Azure (and the best way for most people who want to get an idea of what it’s like to use Azure) is to sign up for a one-month free trial. The trial includes a $200 Azure credit that can be used for any Azure services. The free trial offer is available here:

      http://azure.microsoft.com/en-us/pricing/free-trial/

      To sign up, you will need a Microsoft Account (formerly known as a Windows Live ID), a phone number, and a credit card. Nothing is charged to the credit card, nor will anything be charged to the credit card – by default, once you hit the $200 Azure spend, the account is suspended. You have to agree to pay for services beyond the included $200 and change the default configuration to a Pay-as-You-Go subscription before any expense is incurred. A credit card is required for identity verification only. Once the 30 days has expired, again by default, the account is deactivated and all services removed unless you have converted the account to Pay-as-You-Go. Of course, you can always simply buy Azure services on a Pay-as-You-Go basis and be billed for the service used at the end of each billing cycle.

      As you can imagine, any kind of public cloud service where VMs can be run for free is attractive to people with dubious intentions, such as running botnet services and even mining crypto currencies. Microsoft, like all public cloud services, tries to ensure trial services are used in the spirit they are intended: to try out Azure.

      Azure Benefits from MSDN Subscriptions

Another great way to experiment with Azure (and even use it on an ongoing basis as part of development and testing) is to leverage the Azure benefits that are part of Microsoft Developer Network (MSDN) subscriptions. MSDN subscriptions are a paid service that enables access to pretty much all Microsoft software. It is intended to be used as part of development and testing efforts. Also included with MSDN subscriptions is a monthly Azure credit, which varies depending on the level of the MSDN subscription, as shown in Table 1.1. (The credits are accurate as of this writing, but they could change over time.) Additionally, the MSDN Azure credits go further than regular Azure spending since the OS licenses are part of the MSDN subscription. Windows virtual machines are 33 percent discounted, as are some other services. Benefits for MSDN Ultimate subscriptions are documented on the MSDN Azure benefits details page:

      http://azure.microsoft.com/en-us/offers/ms-azr-0063p/

Table 1.1 MSDN Azure benefits

      http://azure.microsoft.com/en-us/pricing/member-offers/msdn-benefits-details/

      Like the Azure trial accounts, by default the MSDN Azure benefit accounts will not allow you to exceed the Azure credits associated with your MSDN subscription. When your monthly limit is reached, your services will be stopped until the start of the next billing month. You need to manually disable the spending limit and specify a credit card if you wish to use more than the Azure benefit credits each month. With the highest-level MSDN subscription (Ultimate), it’s possible to run three standard-service single-core virtual machines with just under 2 GB of memory all month, which is a pretty nice testing environment. It is important to note that the MSDN Azure benefit is for development and testing only and cannot be used to run production services. Microsoft can shut down your services if it finds they are being used for production purposes.

      Most Microsoft-focused developers already have MSDN subscriptions, so this is a great way to get Azure services to continue that development into the cloud. When I talk to customers about the MSDN benefit, a common question I hear is: “We have lots of MSDN subscriptions – can we pool all the Azure credits together to use as an organizational credit pool?” The answer is no, there is no way to pool MSDN Azure credits together – they are designed to be used by the individual MSDN subscriber for their test and development efforts.

As

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