The role of ADCs

Insightful analysis by consultants Steve Taylor and Jim Metzler, plus links to the latest WAN news headlines

In our last newsletter, we discussed some of the IT initiatives that provide significant value, but which often result in unacceptable application performance. We also mentioned that one way that IT organizations respond to these challenges is by implementing an Application Delivery Controller (ADC) from companies such as F5, Citrix, Cisco, Brocade, A10, Crescendo or Radware. In this newsletter we will discuss how an ADC differs from a traditional server load balancer.

What's driving Application Delivery 2.0?

Most IT organizations have implemented server farms that users typically access over a WAN. A server farm is a group of servers that are networked together with the goal of meeting requirements that are beyond the capability of a single server. One of the challenges associated with implementing a server farm is to ensure that a request for service is delivered to the most appropriate server. There are many ways to define what the phrase most appropriate server means. Certainly the server has to be available. Ideally, the most appropriate server is the server that is processing the lightest load of any of the members of the server farm.

To continue reading, register here and become an Insider. You'll get free access to premium content from CIO, Computerworld, CSO, InfoWorld, and Network World. See more Insider content or sign in.

In our last newsletter, we discussed some of the IT initiatives that provide significant value, but which often result in unacceptable application performance. We also mentioned that one way that IT organizations respond to these challenges is by implementing an Application Delivery Controller (ADC) from companies such as F5, Citrix, Cisco, Brocade, A10, Crescendo or Radware. In this newsletter we will discuss how an ADC differs from a traditional server load balancer.

What's driving Application Delivery 2.0?

Most IT organizations have implemented server farms that users typically access over a WAN. A server farm is a group of servers that are networked together with the goal of meeting requirements that are beyond the capability of a single server. One of the challenges associated with implementing a server farm is to ensure that a request for service is delivered to the most appropriate server. There are many ways to define what the phrase most appropriate server means. Certainly the server has to be available. Ideally, the most appropriate server is the server that is processing the lightest load of any of the members of the server farm.

In order to ensure that a client's service requests are delivered to the most appropriate server, a new product category was developed a number of years ago. That product category is the server load balancer (SLB). A user’s incoming request for service is directed to an SLB. Based on parameters such as availability and the current server load, the SLB decides which server should handle the request and forwards the request to the selected server. The value provided by an SLB is that it enables an IT organization to add servers to a server farm and be confident that the expanded server farm will be able to process a proportionate number of additional transactions. For example, if an IT organization doubles the number of servers, it should be able to process roughly twice as many transactions.

An SLB, however, does not offload any processing from the servers and hence does not increase the overall ability of an individual server to process transactions. An ADC functions in part like a traditional SLB in that it directs requests for service to the most appropriate server. An ADC, however, also offloads computationally-intensive, communications processing off of the servers and hence an ADC can significantly increases the overall ability of a server to process transactions and increase security.

Our next newsletter will discuss the specific functionality provided by an ADC. In the mean time, we could use your help. We are conducting a survey the goal of which is to identify which application delivery challenges are the most important to IT organizations this year. The survey should not take more than 10 minutes to complete and we will share the results with everyone who takes the time to fill out the survey. You can access the survey here.

Read more about lans & wans in Network World's LANs & WANs section.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.