Balancing the Virtual Load
As computer hardware becomes increasingly more powerful, organizations are reaping huge cost and energy savings from replacing physical machines with virtual ones.
But whether you're replacing several physical servers with virtual machines running on a single host, streaming virtualized desktops to thin clients, or delivering virtual applications, if you don't balance the load on your resources your entire network can come screeching to a halt.
Think of load balancers as traffic cops, says Lew Smith, director of business development and virtualization solutions for consultant Interphase Systems. The devices keep the bits flowing smoothly to optimize performance, manage resources and ensure redundancy.
"Without load balancing, you'll get networking bottlenecks and reduced performance from apps," says Smith. "It's like comparing a five-lane highway to a two-lane road. Both can handle the same number of cars, but the two-lane road will take a lot longer."
Like the machines themselves, load balancing can be physical or virtual. Smith says most enterprises deploying virtualized environments use a combination of both: dedicated hardware appliances to manage data traffic coming in from the Internet or across internal networks, plus load balancing software to route data efficiently between physical layers and virtual ones.
When Georgia's Fulton County moved to virtual servers in 2007, it replaced its worn-out WinTel servers with Fujitsu Primergy Blades running VMware ESX and relied on VMware's Distributed Resource Scheduling (DRS) to intelligently manage the load.
"VMware's load balancing gives a lot of flexibility," says Keith Dickie, assistant director of the Fulton County Department of Information Technology.
"We can tell it to segregate virtual servers so they're never on the same blade, and how aggressive to be in migrating virtual machines to new hosts," he says. "If we have a server running 10 virtual machines and need to bring it down for maintenance, DRS can simply find the blades that have the most resources and spin up new VMs automatically."
Server virtualization has been so successful, says CTO Jay Terrell, that Fulton County is embarking on a desktop virtualization proof of concept -- replacing the 700 public-facing computers in the county library system with thin clients, and streaming the operating system and apps to each via VMware.
When the county rolls out the system, it will rely on DRS to ensure consistent performance across each of the county's 34 libraries.
"Not all of our libraries are sized the same," he adds. "Large concentrations of our 700 machines are in the central and regional libraries. With load balancing we can ensure that people who use the small community branches get the same the level of performance everyone else gets."
650%: Anticipated growth in enterprise data over the next five years
Source: Gartner
As ISP for the state of Delaware, the Delaware Department of Technology and Information couldn't afford to let web traffic demands overwhelm the 25 agencies and 19 school districts it serves. So when DTI looked to replace its aging load balancers, it opted for Cisco's Application Control Engine (ACE) module. In concert with Cisco Catalyst 6500 Series switches and VMware ESX, the ACE's virtual architecture allows seamless data exchange across virtual machines on the network.
"All web traffic and browsing for the state agencies goes through ACE," says Scott Huffman, DTI telecommunications tech. "It load balances a set of proxies and then sends them out to the Internet."
The ACE solution was also less expensive, took up less rack space, offered greater redundancy and had much more resiliency, says Huffman. For example, if Microsoft Exchange failed with DTI's previous solution, it took the department at least 30 minutes to restore e-mail service. Now, with ACE and Cisco's Global Site Selector load balancing appliance, DTI can achieve almost instantaneous failover with no interruption of service.
"It was a pleasant surprise to discover how much easier the ACE interface was to interact with than our previous solution," he says. "We appreciated the ability that it gave us to manage different roles and to ultimately allow our other agencies to manage for themselves."
Lifting the Load
Here are three tips for managing load balancers in a virtual environment.
- Think big picture. Load balancing needs to happen everywhere bits flow -- across internal networks, between applications, between physical and virtual layers and from storage to memory and back. Always provide at minimum one level of high availability and redundancy at every layer.
- Measure twice, architect once. Monitor how data flows across your physical environment before you implement a virtual one so you can allocate enough resources for peak traffic needs. Without sound data, captured over a period of time, it's nearly impossible to architect a solution that can handle peaks and valleys of performance intelligently.
- Choose the right level of automation. If you have sudden spikes in demand -- such as "boot storms" when team members log on at the same time each morning -- set your virtual infrastructure to intelligently seek out resources and scale as needed. Otherwise, opt for a more balanced setting or even manual override.
