Dan Feller on my team contributed at least two posts on the topic of virtualizing XenApp servers on XenServer. Dan makes some excellent points and gives you plenty of business reasons why XA on XS is a good idea.

I am not going to re-iterate Dan's points here, but rather focus on another burning question in this context: How much of a scalability overhead can I really expect with my specific application? The typical consulting answer would be "it depends" and "we'll have to do a scalability / performance assessment to determine the specifics and best practices". So, we have done just that and used two popular enterprise class Applications: Siebel 8.0 and PeopleSoft 9.0. The Solution Center is one of the teams under the umbrella of Worldwide Consulting Solutions (Dan Feller's Integrated Solutions team is another) and focuses on these types of projects, which often involve third party applications and/or hardware platforms from our technology partners.
Recently, we looked at running the front-end of Oracle's PeopleSoft and Siebel applications on XenApp (both 32-bit and 64-bit platforms) and focused on comparing the user densities we could achieve on "bare metal" servers compared to running them on XenServer.
The results are published in two separate whitepapers (PeopleSoft, Siebel), which describe the test bed, test methodology, detailed results and interpretation. As Dan stated in his May 15th posting, the virtualization overhead can be as low as 6% for XenApp virtualization on XenServer, and our tests confirm this number. Of course, the numbers vary between the applications and platforms, and we describe all the details in the whitepapers.
Generally speaking, kernel memory limitations constitute the first bottleneck on 32-bit platforms, and our tests verified that behavior. Even with the popular /PAE switch, the kernel memory limitation remains at 2 GB. Therefore, you can expect a higher user density per physical server if you're running multiple 32-bit XenApp servers on a XenServer. You'd have to be cautious not to consume too many CPU cycles, which often become the next bottleneck once memory is no longer a major concern. Prices of multi-core, multi socket servers with plenty of RAM have come down significantly, so chances are that your latest servers have plenty of resources to run reliably in that configuration at a reasonable price:

According to this 1988 article, prices of 1 MB memory chips were as high as $60 (or $105 in today's money), while you can buy a barebones server with 64 GB of RAM for roughly $5,000 today. While I am on the topic of computer nostalgia: a 150 MB hard drive set you back over $8k in today's dollars way back when... 1988 was also the year Dan Feller was looking forward to seeing his favorite TV show getting its own slot in the line up and he is still enjoying it to this day, as you can see from the quotes in his postings on this site. But I am digressing...

The Solution Center also conducted detailed validation tests with Oracle to obtain validation status for running virtual images of the Web-, Application-, and Database servers of Siebel 8.0 , PeopleSoft 9.0, and Oracle E-Business Suite 12 on XenServer 4.1, so you can now be confident that the entire environment can be successfully virtualized on XenServer, allowing you to take advantage of XenMotion in case of hardware failure and other benefits.

Policies are used to configure various Citrix NetScaler Application Switch features. For example, the parameters for compressing content are defined in a compression policy.

The features that use policies are:

• Load Balancing
• Content Switching
• Content Filtering
• AppCompress
• Cache Redirection
• SSL VPN
• Priority Queuing
• DoS Protection
• Sure Connect

Policy expressions are applied to content that enters the switch. Expressions are shared among features, but actions are feature-specific. For example, you can create an expression to identify .pdf files being sent through the system. You can then create a compression policy that uses this expression to compress those files. The Policy Engine (PE) refers to the architecture in the Citrix NetScaler Application Switch for versions up to 8.x. The architecture for Policy Engine and the manner in which it operates is presented in this Deployment Guide.  Did you know that each feature in the Citrix NetScaler Application Switch is processed in a certain order, and the Policy Engine (PE) applies policy according to that order.  That order is represented in this diagram and discussed in the Deployment Guide for Policy Engine (PE).

Watch this Policy Engine Tip:

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As web applications grow in complexity, the art of accelerating them seems to remain the same. This art is performed by applying some basic concepts to the application; that is, Caching, Compression, Load Balancing, Global Server Load Balancing, SSL Offload & Acceleration, Content Switching, TCP Multiplexing and SSL Session Reuse.

Citrix® is a leader in Gartners magic quadrant for Application Delivery with their flagship appliance NetScaler®. NetScaler accelerates web application performance by leveraging multiple acceleration technologies and innovative TCP optimizations.

Whether you are building out a new datacenter and architecting it the right way, or retrofitting an existing datacenter, Citrix NetScaler will perform and keep costs down. Whether you are looking to accelerate legacy enterprise applications such as Oracle or SAP, or building a new web 2.0 social community, Citrix NetScaler contains all of the tools to get you there.

Citrix NetScaler web application delivery solutions are purpose built appliances that accelerate application performance, while simultaneously reducing datacenter costs and improving web application security. Platforms range from the entry level 7000 to the latest MPX-series appliances that provide an industry-leading 15 Gbs of throughput at Layers 4 through 7.

There's more here: Case Studies, White Papers, Analysts , Datasheets

Check out the new MPX!

Buy it here!

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Becoming an Application Expert means that you can profile an application and quickly determine how it can be architected or re-constructed for higher performance. Of course, we want you to use the Citrix Application Switch as part of the architecture. In Part 1, we learned how to profile an application to learn what it looks like as the traffic flows through the Citrix Application Switch. Now we will determine what parts of an application are cacheable and what parts are non-cacheable.

By Application Profiling we can determine which parts of the application are cacheable and non-cacheable just by looking at the Request and Response headers. The application will sometimes tell you through it's "Cache-Control" header directives. Some content that we just know is static and doesn't ever change, we can consider cacheable as static content. Content that changes, such as reports, are often considered non-cacheable but with the help of Selectors and Dynamic Content Groups in the Citrix NetScaler, this content can be cached. As a proof of concept, we deployed the Citrix NetScaler Application Switch in the front of Oracle E-Business Suite v12 application and implemented caching policies for both static and dynamic content. As it turns out, alot of static content is cached by default policies and setting up dynamic policies is not that difficult. To see how, read the Caching Deployment Guide for Oracle E-Business Suite v12.

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Application Profiling

Introduction:

I can turn you into an Application expert in 5 minutes by reading this post.  Just do what the experts do, or even the not-so-experts.  They pay meticulous attention to the requests from clients and the responses from servers, both headers and body content.  You do this the old fashioned way by taking a trace.  There are better tools out there, some free, some not-so-free.

Running a trace:

Running a trace will help you 'profile' the application. It is recommended that you do this before placing the Citrix Application Switch in-line of the Application traffic. This will gather important information about the Application that will help you understand it's basic operation at Layer 7, and help you begin to understand what it is that needs to be accelerated - cached, compressed, load balanced, ssl offloaded, etc.

Running a trace exposes the flow of transactions between all points of interest. Traces are especially helpful when digging in to find what is contained within the headers being exchanged between the client and the application.

Taking a trace with wireshark:

The free network protocol analyzer called wireshark, http://www.wireshark.org, will capture packets for you on the localhost, whether it's windows or linux. By filtering the stream of packets by IP Address, right clicking and selecting 'Follow TCP Stream' inside of wireshark, you can see the headers for both requests and responses.

Wireshark tip 1 Find the first 'SYN' in the stream, right click, 'Follow TCP Stream'.

Wireshark tip 2 Client requests are in Red, Server responses are in Blue.

Taking a trace with the Citrix Application Switch:

If the Citrix Application Switch is already in place, a trace can be run directly on the Citrix Application Switch. Running a trace will expose the flow of transactions between all points of interest, especially the client, load balancing VIPs and backend servers. Traces are especially helpful when digging in to find out if the proper headers are being exchanged between client & VIP and VIP & backend servers. A trace can be run directly on the Citrix Application Switch. Once downloaded this file can be opened and request and response headers read with Wireshark, a free network trace utility, http://www.wireshark.org. From the Citrix Application Switch GUI, navigate to NetScaler -> System -> Diagnostics -> New Trace -> Run. 

Viewing headers with Paros:

Paros was originially written for web security, but has value when viewing request and response headers, cookies and the like. Through Paros's proxy nature, all HTTP and HTTPS data between server and client, including cookies and form fields, can be intercepted. There is an additional option of trapping and modifying data before sending it on to the server, or client. Paros can be found at http://parosproxy.org. Free.

Viewing headers with Live HTTP Headers:

Live HTTP Headers, http://livehttpheaders.mozdev.org/, was developed for use with the Firefox web browser. It is a free add-on and allows you to view HTTP header information in real time. Free.

Viewing headers with IE Analyzer:

IEInspector HTTP Analyzer, http://www.ieinspector.com, is a tool that allows you to monitor, trace, debug and analyze HTTP/HTTPS traffic in real-time. It works with Microsoft Internet Explorer. Not-Free.

Viewing headers with IE Watch:

IEWatch, http://www.iewatch.com, is another plug-in for Microsoft Internet Explorer that helps you profile your web applications. You can use this tool to dig deep into the inner workings of web applications to find hidden issues. Not-Free.

Watch this Application Profiling Tip:

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