Note: Refer to the man page "man add ns variable" for description of the command parameters.

Example 1: Create a ulong variable named "my_counter" and initialize it to 1.

Example 2: Create a map named "user_privilege_map". The map will contain keys of maximum length 15 characters and text values of maximum length 10 characters, with a maximum of 10000 entries.

Note: If the map contains 10000 unexpired entries, assignments for new keys reuse one of the least recently used entries. By default, an expression trying to get a value for a non-existent key will initialize an empty text value.

Assign the value or specify the operation to be performed on the variable. This is done by creating an assignment.

Note: A variable is referenced by using the variable selector ($). Therefore, $variable1 is used to refer to text or ulong variables. Similarly, $variable2 is used to refer to map variables.

Example 1: Define an assignment named "inc_my_counter" that automatically adds 1 to the "my_counter" variable.

Example 2: Define an assignment named "set_user_privilege" that adds to the "user_privilege_map" variable an entry for the client's IP address with the value returned by the "get_user_privilege" HTTP callout.

Note: If an entry for that key already exists, the value will be replaced. Otherwise a new entry for the key and value will be added. Based on the previous declaration for user_privilege_map, if the map already has 10000 entries, one of the least recently used entries will be reused for the new key and value.

The following example shows an example of a singleton variable.

Add a singleton variable of type text. This variable can hold maximum 100 Bytes data.

Add an assignment action, which will be used to store the HTTP request data into the variable.

Add a rewrite action to insert HTTP header, whose value will be fetched from the variable.

Add a rewrite policy which will evaluate in the request time, and take assignment action to store data. When we hit this policy, we’ll take assignment action and store the data into the ns variable (http_req_data)

Add a rewrite policy which will evaluate in the response time, and add an HTTP header in the response.

In a NetScaler appliance, an assignment action bound to the policy is triggered when the policy rule evaluates to true. The action updates the value in the variable which can be used in subsequent policy rule evaluations. This way, the same variable can be updated and used for subsequent policy evaluations in the same feature. Previously, the appliance executed assignment actions only after evaluating all of the policies in the feature when the policies of the associated assignment actions evaluated to true. Therefore, the variable value set by the assignment action cannot be used in the subsequent policy rule evaluations within the feature.

This functionality can be understood better with a use case that controls access list for clients on a NetScaler appliance. The access decision is provided by a separate web service, with the request GET /client-access?<client-IP-address> which returns a response with “BLOCK” or “ALLOW” in the body. The HTTP callout is configured to include the IP address of the client that is associated with an incoming request. When the NetScaler appliance receives a request from a client, the appliance generates the callout request and sends it to the callout server, which hosts a database of blacklisted IP addresses and an HTTP callout agent that checks whether the client’s IP address is listed in the database. The HTTP callout agent receives the callout request, checks whether the client’s IP address is listed, and sends a response. The response is a status code, 200, 302 along with “BLOCK” or “ALLOW” in the body. Based on the status code, the appliance performs the policy evaluation. If the policy evaluation is true, the assignment action is triggered immediately and action sets the value to the variable. The appliance uses and sets this variable value for subsequent policy evaluation in the same module.