Cloud computing is transforming the traditional server application tiers into mobile, virtualised containers. As applications and servers are abstracted from the infrastructure, this severs their easy integration with the systems used to provide for availability, performance, and security.
As a result, more organisations are prompted to examine a critical fourth tier within the data centre architecture — a flexible and highly scalable tier in which application delivery concerns such as security, performance, and availability can be addressed.
The application delivery tier is based on an Application Delivery Network, a set of services that addresses and mitigates the operational risks that hinder the successful deployment and delivery of applications. At the heart of the Application Delivery Network is the Application Delivery Controller (ADC).
ADCs, most often associated with load balancing to address availability and performance issues, have evolved to provide services to mitigate security threats, ensure availability, and improve performance within the data centre and into the cloud.
What to look for when choosing an ADC?
ADCs should be evaluated against functional criteria that include:
• Manageability and
Performance is a primary concern. An ADC is logically deployed between end-users and applications to provide delivery services. Its performance, therefore, is a critical consideration.
In evaluations, connection capacity and decisions-per-second are far more important than mere speeds and feeds. Often, it is either capacity or transaction rate that is the bottleneck that drags the performance of applications.
The number of connections necessary to meet demand is rising. Connection management is a common cause of application performance problems. It not only consumes resources that cannot be used to process requests, it also consumes additional time per request as applications search longer and longer lists of connections before identifying the most efficient one. On web and applications servers, performance is directly related to connection management.
An ADC can mitigate this problem by mediating for the servers and limiting the number of connections that must be opened without impacting the number of users that can be served concurrently. This enables the ADC to sustain large numbers of connections without negatively affecting performance.
Connection capacity becomes more critical as application-layer attacks increasingly bypass traditional security measures and threaten the infrastructure with an overwhelming number of connections.
Transactions per second
Behavioural changes in applications such as the increasing reliance on APIs for mobile applications, make it important to evaluate an ADC’s ability to make decisions at an acceptable rate.
Consider the difference between a simple HTTP request and response in which the request is nothing more than a GET request paired with a zero-byte payload response, a POST request filled with data that requires processing not only on the application server but on the database, and the serialisation of the response. The metrics that describe the performance of these two requests will almost certainly show that a GET request has a higher capacity and faster response time than a POST request.
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