Load Balancing Traffic on a Citrix NetScaler

Load Balancing Traffic on a Citrix NetScaler

Load balancing improves server fault tolerance and end-user response time. This chapter lists the basic and a few advanced settings that you can configure.

In This Chapter

How Load Balancing Works

Configuring Load Balancing

How Load Balancing Works

The load balancing feature distributes client requests across multiple servers to optimize resource utilization. In a real-world scenario with a limited number of servers providing service to a large number of clients, a server can become overloaded and degrade server performance. A NetScaler uses load balancing criteria to prevent bottlenecks by forwarding each client request to the server best

suited to handle the request when it arrives.

To configure load balancing, you define a virtual server (vserver) to proxy multiple servers in a server farm and balance the load among them. When a client initiates a connection to the server, the vserver terminates the client connection and initiates a new connection with the selected server to perform load balancing. The load balancing feature provides traffic management from Layer 4 (TCP and UDP) through Layer 7 (FTP, HTTP, and HTTPS).

The NetScaler uses a number of algorithms, called load balancing methods, to determine how to distribute the load among the servers. The default load balancing method is the Least Connections method.

The entities that you must configure in a typical load balancing setup are:

• Vserver. An entity that is represented by an IP address, a port, and a protocol. The vserver IP address (VIP) is usually a public IP address. The client sends connection requests to this IP address. The vserver represents a bank of servers.

• Service. An entity that is represented by an IP address, a port, and a protocol. A service is a logical representation of a server or an application running on a server. The services are bound to the vservers.

• Server object. An entity that is represented by an IP address. The server object is created when you create a service. The IP address of the service is taken as the name of the server object. You can also create a server object and then create services by using the server object.

• Monitor. An entity that tracks the health of the services. The NetScaler periodically probes the servers using the monitor bound to each service. If a server does not respond within a specified response timeout, and the specified number of probes fails, the service is marked DOWN. The NetScaler then performs load balancing among the remaining services.

To configure load balancing, you must first create services. Then, you must create vservers and bind services to the vservers. By default, the NetScaler binds a monitor to each service. You can also assign weights to a service. The load balancing method uses the assigned weight to select a service. You need to perform these tasks in the sequence illustrated in the following flow chart.