Boosting Virtual Server Scalability with Citrix NetScaler

Overview

Server Consolidation... Green Computing... Centralization... Each one is a common reason why organizations move towards a server virtualization solution. While functional separation created the need for many separate servers, organizations can reduce the number of physical servers by converting them into virtual servers. Multiple virtual servers can now be hosted from a single physical server running a number of products such as XenSource, VMware ESX, Microsoft Virtual Server and Virtual Iron. Any number of virtual server technologies can help stop server sprawl and more fully utilize physical servers, but more can be done The first step in building a more efficient application delivery infrastructure, which relies on server virtualization solutions, is to migrate from the physical into the virtual. This process reduces the number of physical servers. However, as this process continues, the physical server that hosts the virtual servers will run out of capacity and a new physical server is required and the sprawl begins again, albeit at a slower pace. It is true, by combining multiple virtual servers onto a single physical server will result in more fully utilized servers, but is the utilization efficient? Physical or virtual, the server's performance and scalability is still impacted by user requests, response generation and data transmission. By optimizing these processes, the impact on a virtual server will reduce, which in turn lowers the utilization on the physical server thereby allowing the physical server to host more virtual servers. Citrix NetScaler integrated with the virtual server solution can continue to further reduce the number of systems required to support the organization, thereby helping with the goals of server consolidation and green computing. This article summarizes how an application delivery infrastructure can be further optimized and consolidated with a NetScaler and virtual server integrated solution. The following areas of focus are:

• Traffic Management
• Compression
• Caching

Scalability Improvement Areas

Many virtual server architectures are used to consolidate multiple resources onto a single, powerful server. Oftentimes, web servers, backend systems or application front-ends are virtualized and hosted as virtual servers. The following sections will explain how NetScaler can improve the responsiveness and scalability of the virtual servers, which improves the scalability of the physical server.
Integration Reference NetScaler 8.0

Traffic Management

Dealing with requests, encryption and decryption operations costs servers a great deal of computing power. The overall performance, scalability and reliability of a virtual server solution can be improved with the following traffic management capabilities of NetScaler:

• TCP Optimization: Each request requires a web server to setup and teardown a TCP connection. As this process expands to hundreds, thousands or millions of requests, this process takes more time, costs more CPU cycles, and impacts the overall scalability. With NetScaler, a multiple TCP connections can be setup and maintained while thousands of session requests are tunneled through the NetScaler connections. This solution improves the virtual server's performance and helps to increase scalability of the virtual and physical server.
• TCP/SSL Offload: Requiring web servers to encrypt/decrypt SSL traffic, exchange keys and perform SSL handshakes is a processor intensive task. Allowing NetScaler to take over the SSL process frees up processor cycles from the virtual web servers, thus allowing the server to service more user requests.
• Global Server Load Balancing: Typically, multiple web servers are used to host a single web application to provide redundancy and to provide the performance needed. Virtualizing those web servers and hosting them on the same physical server is a single point of failure, requiring the need to distribute the virtual servers across multiple physical servers. Also, for web applications with a global reach, significant usability improvements can be garnered by placing those servers in different data centers around the world. By using the Global Server Load Balancing functionality within NetScaler, users located anywhere in the world will always end up connecting to the site that is the closest, fastest, or has the least load. This helps to provide the users with the best web access experience.

Compression

Most traffic sent from a server is not optimally compressed, utilizing valuable bandwidth. Also, compressing data takes resources away from the system's main purpose of hosting information for users. By integrating the following NetScaler features into a virtual server solution, performance and scalability can be positively impacted:

• Web Compression: Performance can be improved by reducing the amount of data sent from web servers to browsers. The Citrix AppCompress technology compresses application responses sent to clients in order to reduce the latency experienced by the application user, while remaining completely transparent to clients. Besides accelerating the delivery of application data to users, AppCompress offloads web servers from performing computer-expensive compression operations. This enables organizations to serve much larger user populations without adding additional server hardware or virtual servers.
  

Caching

Oftentimes, multiple users end up requesting the same data, requiring the server to perform roughly the same operations over, and over again. As these types of tasks are redundant, removing them from the web server would help increase scalability. By integrating the following NetScaler features into a virtual server solution, performance and scalability can be improved:

• Static Content Caching: Citrix's AppCache technology is in-memory storage of static web content, like images, thereby reducing the impact on the web server from having to repetitively generate the same application data requested by multiple users. In addition, integrated content caching provides faster application delivery since popular content can be served immediately out of memory, with minimal data generation cost.
• Dynamic Content Caching: Many web applications host dynamically generated content, thereby negating the benefits of standard caching mechanisms. However, Citrix's AppCache technology uses custom-defined parameters to determine whether the content in a specific application response can safely be cached and served to the user. The AppCache technology also has safeguards in place to prevent outdated information from being served to the user.

Summary

Server virtualization focuses on server consolidation, reducing energy costs and more fully utilizing purchases resources. Many organizations have started down the path of server virtualization; they have slowed the sprawl of servers and have increased the overall utilization of their systems. Every organization that started down the path of server consolidation and green computing should not stop with only server virtualization, they should continue with server consolidation, slow server sprawl and save more money by reducing power consumption. This is what NetScaler can do when integrated into a virtual server solution.

• Users will experience faster response times
• The scalability of the virtual servers will increase
• The physical servers will be able to support more virtual servers
• The number of physical servers required will decrease
• The organization will provide a better application delivery experience to the user while saving on infrastructure costs

The NetScaler technologies of AppCache, AppCompress, and the set of Advanced Traffic Management solutions will help to improve the scalability and reliability of virtual web servers by offloading costly operations and placing them onto the NetScaler.