Quickly configure policies and rules
As an ADC, NetScaler consists of many features and modules, and all of them require runtime intelligence and decision making ability. In today’s environment, we rarely see a pure load balancing deployment working at a plain L4 layer. For most of the common use cases, one needs to perform runtime decision making based on actual traffic content, which then requires taking various actions to fulfill application needs. For this very purpose, NetScaler supports AppExpert or the advance policy infrastructure which provides core capabilities to work on Layer 7.
Advance policy infrastructure consists of extremely powerful expression language spanning from Layer 2 to Layer 7. You can define all possible expressions getting to the most atomic level as per protocol RFCs. The expression language can be used to define Rules in Policy, define various parts of Action, and other entities supported. The expression language can parse through any part of the request/response and also enables you to look deeply through the headers and payload. The same expression language expands and works through every logical module NetScaler supports. The expression language also has the capability to invoke any AppExpert tool available on NetScaler, helping build interesting use cases. More than anything else, the expressions are highly reusable and it’s possible to build a huge repository with the help of the NetScaler community.
Now comes the programmability aspect, and we are beginning to build the layer in NetScaler with the recent infrastructure level feature "Variable." We truly believe in keeping things simple and effective and hence our core policy and expression layer was always liked by our customers as it is simple to use and highly effective while it does not require you to be a programmer. Some of the advanced use cases require NetScaler to maintain states and remember tokens, which might be required to make intelligent decisions later in the session lifecycle. Variables help with such use cases and we would further enrich them with rich capabilities.
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