Virtual App Delivery Appliances Emerge

When enterprise IT personnel say they want to "ensure acceptable application delivery," it means they want their applications to do the following:

• Exhibit consistently adequate performance
• Be easy to manage
• Incorporate appropriate security levels
• Be cost-effective

Toward this end, many IT organizations have implemented application delivery appliances such as WAN optimization controllers (WOCs) and application delivery controllers (ADCs). These appliances have typically been deployed as standalone hardware systems. But there's a growing trend to implement virtual application delivery appliances.

As explained in Webtorials' 2011 Application & Service Delivery Handbook, the term "virtual appliance" means different things to different people. For example, with some vendors' products (e.g., A10 Networks), it can mean that multiple ADCs can work together as a single large ADC. Other vendors (e.g., Citrix) can make a large ADC behave as if it were a number of smaller ADCs.

Why Do It With Software?

However, in most cases, "virtual appliance" refers to a software instance of the hardware appliance's functions. That software and its associated operating system run in one or more virtual machines (VMs) on top of a hypervisor -  software that partitions a physical server into a number of virtual servers. In addition to WOCs and ADCs, virtual appliances can also include firewalls, intrusion detection/prevention systems, routers and performance monitoring solutions.

One factor driving virtual WOCs and ADCs in data centers is the fact that most IT organizations have virtualized at least some of their servers to maximize physical server utilization and decrease hardware, real estate and aggregate power and cooling costs. As a result, many enterprise data centers already have VMs that can be used to host a virtual WOC or a virtual ADC.

In a branch office, a suitably placed virtualized server could potentially host a virtual WOC appliance and other virtual appliances, forming what is sometimes referred to as a "branch office in a box." Alternatively, a router or WOC that supports VMs could also serve as the infrastructure foundation of the branch office. Virtual appliances can therefore support branch-office server consolidation strategies by enabling a single device (i.e., server, router, WOC) to perform multiple functions that traditionally have required multiple physical devices.

A compelling advantage of a virtualized application delivery appliance is that its acquisition cost can be notably less - sometimes by as much as a third - than that of a hardware-based appliance with identical functionality. In addition, a software-based client can potentially leverage the functionality provided by the hypervisor management system to provide a highly available system, eliminating the need to pay for a second backup appliance.

Another key advantage is that virtualized application delivery appliances help IT organizations implement a dynamic data center. For example, one challenge  with migrating a VM between physical servers is replicating the VM's networking environment in its new location. Virtual appliances, unlike their physical counterparts, can be easily migrated along with the VM, making it easier to replicate the VM's networking environment at its new site.

What About Performance?

Conventional IT industry wisdom holds that a potential downside of virtual application delivery appliances is lower performance. A dedicated, purpose-built hardware appliance is generally thought to perform better than one in which software is ported to a generic piece of hardware, particularly if that hardware is supporting multiple applications.

However, conventional wisdom is often wrong.  Some of the factors that enable a virtualized appliance to provide high performance include the following:

• Moore's Law, which states that the price/performance of off-the-shelf computing devices doubles every 18 months
• The deployment of multiple core processors, which further boosts the performance of off-the-shelf computing devices
• The optimization of the software on which the virtual appliance is based

Mixed Opinions

The vendor community is of a mixed mind on the topic of virtual application delivery. Some ADC vendors, such as Riverbed and Citrix, are strong proponents; others, such as F5, are less bullish. Similarly, some WOC vendors, such as Silver Peak and Exinda, are strong backers of virtual WOCs, while others, such as Riverbed, are not.

I will moderate a session at the Interop Las Vegas Conference and Expo, to be held at the Mandalay Bay May 6 -10, 2012, titled, "Is this the End of Physical Appliances?" The session, to be held Tuesday, May 8 at 2:30 p.m., will identify the pros and cons of virtual appliances and discuss implementation considerations. Please attend, learn more about this important topic and provide your input.