Citrix NetScaler meets the need for speed
Version 8 of Citrix's Web application delivery appliance combines rich acceleration features and easy administration, offering a good value to large and busy sites
The NetScaler supports both integrated caching and the use of an external cache server. In either case, requests for content coming from clients are served from the cache rather than from the Web server. A multitude of options ensures that frequently changing content is fetched from the Web server rather than cache, or that the cached data is updated regularly. You can choose to cache only static content or use a flexible set of rules to determine when to cache dynamic content.
TCP buffering is useful because the network between Web servers and the NetScaler is invariably much faster and more responsive than the Internet. By holding responses from Web servers until clients are ready to receive them, the NetScaler reduces the chattiness between Web servers and clients, freeing server memory and lowering CPU utilization. If the Web server is heavily loaded, this can make a dramatic difference; on lightly loaded servers, the effect is not noticeable.
TCP session consolidation (sometimes called session multiplexing) keeps all requests between the server and a client in one TCP/IP session. Because the overhead of starting a session is fairly large (some Web browsers can start dozens or even hundreds of TCP sessions to display a single page), session consolidation can improve performance substantially. Modern Web servers can implement session persistence as well, in which case the NetScaler's TCP session consolidation will not improve performance. However, offloading this function to the NetScaler will reduce server loads, and may be much simpler than implementing the feature on the Web server.
Compression is another feature that produces greatly variable results. The algorithms used to compress text and HTML are part of the HTML 1.1 and later specification. All recent browsers support compression, and on largely text or HTML pages the differences in display times can be dramatic. Pages with active content or graphics that are already compressed will show minimal gains.
Given the high profile that security has gotten during the past few years, many sites implement SSL encryption for nearly everything. Computing the codes necessary to encrypt and decrypt traffic between server and client can put substantial loads on the Web server. SSL offload uses a dedicated encryption processor to encrypt and decrypt traffic, removing the load from the Web server. This is another technology that will not improve performance on lightly loaded Web servers but can reduce CPU utilization on heavily burdened Web servers by a third to a half, greatly improving server response times.
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Setting up the NetScaler is easy. Initial configuration can be done with a serial terminal, or via the default IP address using a Web browser. Using the NetScaler interface from a browser in other than a basic monitoring mode (including using the dashboard for full monitoring capabilities) requires a Java client, which is automatically downloaded from the NetScaler. The interface is clean and easy to navigate, with context-sensitive help that can get you through at least the basics. Beyond that, documentation is extensive, available on the NetScaler itself rather than being provided on a CD or as hard copy.