Load Balancing

A crucial piece of knowledge to being an Application Expert is providing availability and offload of the backend servers across any TCP port number. Most web applications run on port 80 and 443. Some enterprise applications use custom ports. Either way, if you want to optimize the performance and keep clients connected when one of the servers or applications starts to fail, you will need a Load Balancer such as the Citrix Application Switch.

Load balancing allows you to distribute incoming requests to a particular virtual server (vserver or VIP) evenly across several backend physical servers. This is also known as Server Load Balancing (SLB). The virtual server runs load balancing algorithms within the Citrix Application Switch.

A vserver consists of a combination of an IP address, port, and protocol that accepts incoming the traffic. The vserver is bound to a number of physical services running on physical servers in the backend server farm. Typical physical servers range from apache web servers to high-end enterprise applications such as SAP and Oracle.

The way it works is a client sends a request to the virtual server, which selects a physical server in the backend server farm and directs the request to the selected physical server. Load balancing allows the Citrix Application Switch to choose the physical server with the lowest load and greatest available resources and directs the incoming request to that server. The Citrix Application Switch can select from many different algorithms for balancing the load, the most common being Round Robin.

Different virtual servers can be configured for different sets of physical services, for example TCP and UDP services. The Citrix Load Balancer supports protocol/application specific vservers for HTTP, HTTPS, FTP, SSL, SSL BRIDGE, SSLTCP, NNTP, DNS, SIP and SNMP services.

To with with your understanding and first time configuration, this deployment guide speaks directly to configuring Load Balancing and SSL Offload on a Citrix Application Switch. It was developed for the SAP Application, but the concepts apply to any Web Application.

Citrix Load Balancing Deployment Guide.

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