Overview of Virtual Machine Offerings in Microsoft Azure

Microsoft Azure Compute Options

Microsoft Azure provides three major compute options from which you can select to run websites and applications. The first two options, Azure Websites and Azure Cloud Services, are solutions that leverage VMs without requiring you to fully manage their creation and administration. Azure Websites and Cloud Services are Platform as a Service (PaaS) offerings. The third option, Azure Virtual Machines (VMs), provides you with full control to create and manage your VMs. Azure Virtual Machines is an Infrastructure as a Service (IaaS) offering.

Azure Websites

Azure Websites offer you the ability to create and manage websites and web applications without the need to create and manage the underlying VMs on which they execute. In this model, you can select to run your website and web applications on a VM that you share with other customers, or you can elect to have them run on VMs that are reserved solely for your use. Azure Websites run on VMs that are part of a resource pool with load balancing, high-scalability, traffic management, high-availability, and fault tolerance features.

Azure Cloud Services

Similar to Azure Websites, Azure Cloud Services use VMs to execute workloads, but with the addition of giving you some configuration and control over the underlying VMs. For example, you can access the VMs remotely and also install software on Cloud Service VMs, whereas you can only manage your websites and web applications in Azure Websites.

Azure Cloud Services also provide you with the ability to use instances of web roles running on IIS, or worker roles which do not require IIS. If your application is composed of multiple components running on multiple VMs, all of these VMs run in a single cloud service with access to your application through a public facing IP address. Azure Cloud Services support load balancing of incoming requests, as well as fault tolerance through detection of hardware, VM, and application failure. If one or more of the VMs or application instances in a cloud service fail, Azure can automatically start new VMs and new application instances in your cloud service to mitigate service downtime. As part of the configuration of an Azure Cloud Service, you can select from different VM types according to your workload requirements. This is also true if you decide to use Azure Virtual Machines.

Azure Virtual Machines

Azure Virtual Machines offer you complete control of the creation, configuration, and management of VMs to run your applications. You can create virtual machines using your own VHDs that you upload into Azure or by leveraging VHD offerings in the Azure VHD gallery. Microsoft Azure provides VHDs for different editions and configurations of Windows Server, Linux servers (Suse, Ubuntu, CentOS), Microsoft applications such as SQL Server, BizTalk Server, SharePoint Server, and many third-party applications.

Every VM that you create is associated with a cloud service. If your application requires execution across multiple VMs, then all VMs should be grouped in the same cloud service. This configuration allows you to leverage Azure load-balancing across the set of associated VMs. If your application only requires a single VM, it is still associated with a cloud service, but it can be the only VM in that cloud service. VMs in the same cloud service can also communicate with each other using a private virtual network. If you need to connect VMs running in Microsoft Azure to on-premises resources, you can leverage a VPN gateway to establish the network path. This also allows you to enable VMs running in Microsoft Azure to be joined to your corporate Active Directory (AD) domains running on on-premise servers.

Azure Virtual Machines support the configuration and association of multiple data disks to VMs using VHDs. These VHDs are used to store persistent data for your application. Azure Virtual Machines can store VHDs on Azure Standard Storage devices which are hard disk drives (HDD) or on Azure Premium Storage which are Solid State Devices (SSD) that provide high-performance and low-latency I/O operations for more demanding workloads. However, at the time of writing this article (April 2015), only DS-size VMs support connection to Azure Premium Storage.

In terms of fault tolerance, Microsoft Azure Storage provides replication across geographical regions. This allows changes in VM operating system and application data to be preserved in case of a hardware failure in the primary data center.

Azure Virtual Machines offer the most flexibility for storage, connectivity, and configuration. However, you have to maintain your VMs including updating and maintaining the OS and all other applications that run on them.

Azure Virtual Machines Offerings

Microsoft offers Azure Virtual Machines in two tiers (basic and standard) and an array of different sizes (compute, memory, storage, and IOPS configurations). It is up to you to select the right VM size that matches your workload requirements. The VM size that you select also determines the price that you pay for use of the VM. Storage costs are priced separately and depend on the space used in your Azure Storage account.

Basic Tier VMs

As shown in Table 1, the basic tier includes only A series VMs. Microsoft Azure does not support load-balancing and auto-scaling for this tier of VMs.

Table 1: Basic Tier VMs

Standard Tier VMs

The Azure standard tier includes A series (Table 2), D series (Table 3), DS series (Table 4), and G series VMs (Table 5).

Table 2: Standard Tier VMs – A Series

The A8 – A11 VMs are optimized for high-performance computing (HPC) and network intensive applications. The A8 and A9 VMs support two network adapters including one that provides low latency and high-throughput networking using remote direct memory access (RDMA) technology. A10 and A11 VMs support one network adapter and does not provide RDMA.

Table 3: Standard Tier VMs – D Series

The D series VMs provide temporary storage space using SSD disks for additional performance improvements.

Table 4: Standard Tier VMs – DS Series

The DS series VMs provide local storage space based on SSD disks. Either Standard Storage or Premium Storage disks can be connected to DS series VMs as data disks. Premium Storage provides SSD disks instead of the HDD disks offered in Standard Storage. The maximum IOPS achievable depend on the size of the Premium Storage disks selected (P10 – 500 IOPS/disk, P20 – 2300 IOPS/disk, P30 – 5000 IOPS/disk). These VMs also provide caching for higher performance.

Table 5: Standard Tier VMs – G Series

The G series VMs also provide local storage space based on SSD disks. Microsoft Azure offers these VMs configured to run very large, and memory and processor intensive workloads such as relational databases.

Conclusion

Microsoft Azure provides three services to run workloads in virtual machines. Deciding whether you need to select Azure Websites, Azure Cloud Services, or Azure Virtual Machines depends on two basic factors: the type of workload that you want to run in the cloud and the level of control that you need over the VMs that run your workloads. Azure Websites support running websites and web applications with a minimal level of VM control and management. Azure Cloud Services allow you to install software and remotely access VMs running your workloads but without the need to fully manage the VMs. Azure Virtual Machines provide you with full control and management over the VMs including updating and patching the operating system and applications. Azure Virtual Machines provide two tiers of VMs (basic and standard) and different VM sizes (A, D, DS, and G series) to match to your workload requirements.