Citrix Systems 9.2 About Calling Out to an External Application, About Http Callout Policies

186 Citrix NetScaler Policy Configuration and Reference Guide

About Calling Out to an External Application

A callout to an external application consists of an HTTP request and a set of parameters that parse the response to the request. You configure the entire request, or significant parameters in the request, in the HTTP callout policy. The HTTP callout policy also contains information about the recipient of the request and advanced expressions for parsing the HTTP response when it is received.

A callout can send only an HTTP request. The service can only be an HTTP or HTTPS service.

After configuring an HTTP callout policy, you do not bind it or add it to a policy bank, as you would another policy. Instead, you invoke it using an advanced expression in one of the following:

•Content Switching: For content switching of HTTP and TCP data

•Rewrite

•Responder: For content filtering functions

•Load Balancing: For token-based load balancing

Task overview: Configuring a callout to an external application

1.Create a callout policy in the Rewrite feature, as described in “Configuring an HTTP Callout Policy,” on page 188.

2.In the feature where the callout policy is needed, invoke the callout policy from an advanced expression, as described in “Invoking an HTTP Callout Policy,” on page 193.

3.Configure an HTTP callout agent to format the callout to the receiving application, as described in the “HTTP Service Callout” chapter in the Citrix NetScaler AppExpert Guide.

About HTTP Callout Policies

You configure HTTP callout policies in the Rewrite feature. After you define the callout policy, it can be invoked from a policy expression in other NetScaler features. For information on configuring the callout policy, see “Configuring an HTTP Callout Policy,” on page 188. For information on invoking the callout policy, see “Invoking an HTTP Callout Policy,” on page 193.

An HTTP callout policy contains the following components:

•Parameters that identify the application to be queried.