How Load Balancing NetScaler Works

In a fundamental load balancing configuration, clients direct their requests to the IP address of a virtual server established on the NetScalers load balancers appliance. This virtual server then efficiently disperses these requests among various application servers using a predetermined method known as the load balancing algorithm. Occasionally, opting for a wildcard address for the virtual load balancers server rather than a specific IP address can be advantageous.

Citrix NetScaler Load Balancer Basics

Within a Citrix load balancing configuration, there exists a load-balancing virtual server and a network of load-balanced application servers. Operating as the intermediary, the virtual server accepts incoming client requests, employs a load balancing algorithm to choose an appropriate application server, and then redirects these requests accordingly. The visual representation below showcases a common Citrix ADC load balancer setup. Furthermore, an alternative approach involves designating a global HTTP port.

The load balancing virtual server employs various algorithms to regulate the distribution of workload among the servers it oversees. By default, it employs the least connection method, directing incoming client connections to the load-balanced application server with the fewest active user connections at that moment.

In a standard NetScaler load balancing setup, the entities you configure typically encompass:

• The Load Balancing Virtual Server serves as the specific combination of IP address, port, and protocol where clients direct their connection requests for a particular website or application. When the application is accessible from the internet, the Virtual Server IP (VIP) address is a public IP. However, if it’s limited to LAN or WAN access, the VIP typically uses a private (ICANN non-routable) IP.
• A Service represents the combination of IP address, port, and protocol used to steer requests toward a specific load-balanced application server. This service can either symbolize the application server itself or an application running on a server hosting multiple applications. Once a service is created, it’s linked (bound) to a load balancing virtual server.
• The Server Object acts as a virtual entity enabling the assignment of a name to a physical server instead of relying solely on its IP address for identification. Creating a server object allows specifying its name instead of the server’s IP when configuring a service. Otherwise, the server’s IP becomes its identifier while creating a service.
• A Monitor, an entity within the NetScaler appliance, constantly oversees a service to ensure its operational integrity. Through periodic probes or health checks, it monitors each assigned service. If a service fails to respond within the defined time-out after a specified number of health checks, it’s marked as DOWN. Consequently, the NetScaler appliance excludes that service from load balancing until the underlying issues are resolved.
• In a load balancing configuration, the Virtual Server, Services, and Load-Balanced Application Servers can utilize both Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6) IP addresses interchangeably. This setup allows the integration of both IPv4 and IPv6 addresses seamlessly within the same load balancing infrastructure.

Understanding the Topology

In the architecture of a load balancing setup, the load balancing server strategically positions itself as an intermediary between the client and the server farm, orchestrating the flow of traffic towards the servers within this farm. Within the infrastructure of the NetScaler appliance, the application servers are symbolized by virtual entities referred to as services. Below is a visual representation depicting the fundamental topology of a basic load balancing configuration.

Load balancing serves as the mechanism governing traffic distribution among servers. A virtual server takes charge by choosing a service to handle client requests. Picture a scenario where Service-HTTP-1 and Service-HTTP-2 are established and linked to the virtual server named Vserver-LB-1. In this setup, Vserver-LB-1 directs client requests to either Service-HTTP-1 or Service-HTTP-2. Employing the least connection load balancing method, the NetScaler appliance determines which service to allocate for each request. The table below delineates the fundamental entities along with their respective names and values that necessitate configuration on the appliance.

The diagram below illustrates the load balancing sample values and necessary parameters detailed in the table above:

Use of Wildcards Instead of IP Addresses and Ports

There are situations where employing a wildcard for the IP address, port of a virtual server, or the port of a service becomes essential. Consider the following cases necessitating the use of a wildcard:

• Transparent Pass-Through Configuration: When the NetScaler appliance must accept all incoming traffic regardless of the targeted IP or port.
• Non-Standard Listening Ports: If services operate on non-well-known ports.
• Dynamic Port Changes: When services change their listening ports over time.
• Limitation in IP and Port Configuration: Reaching the limit for configuring IP addresses and ports on a single NetScaler appliance.
• Specific Virtual LAN Traffic Handling: Creating virtual servers that capture all traffic on a designated virtual LAN.

Upon receiving traffic, a wildcard-configured virtual server or service prompts the NetScaler appliance to identify the actual IP address or port, generating records for the service and its associated load-balanced application server. These dynamic records are termed “dynamically learned server and service records.”

For instance, in a firewall load balancing setup utilizing wildcards for both IP address and port, binding a wildcard TCP service to such a load balancing virtual server enables it to handle and process all TCP traffic not matching any other service or virtual server.

Outlined below is a table delineating various types of wildcard configurations along with the scenarios mandating their utilization.

The NetScaler appliance employs a sequential search approach to locate virtual servers and services. It begins by seeking an exact match and proceeds through wildcard options in the following sequence:

1. Specific IP address and specific port number
2. Specific IP address and a * (wildcard) port
3. (wildcard) IP address and a specific port
4. (wildcard) IP address and a * (wildcard) port

In cases where the appliance fails to find a virtual server based on IP address or port number, it conducts a search based on the protocol utilized in the request, prioritizing in the following order:

1. HTTP
2. TCP
3. ANY

Configuring Global HTTP Ports

Services or virtual servers aren’t configured explicitly for a global HTTP port. Instead, you employ the “set ns param” command to configure a specific port. Once set, the NetScaler appliance actively manages all traffic aligning with this port, treating it as HTTP traffic, dynamically generating and learning services tailored to this traffic pattern.

Configuring multiple port numbers as global HTTP ports is possible. When specifying multiple port numbers within a single “set ns param” command, separate each port number by a single white space. If there are existing ports designated as global HTTP ports and you aim to append new ones without removing the current configuration, you must list all port numbers—both existing and new—within the command.

Before adding new port numbers, it’s advisable to employ the “show ns param” command to review the currently configured ports.

To Configure a Global HTTP Port by Using the Command Line Interface

To configure a global HTTP port and confirm the setup, follow these commands at the command prompt:

set ns param –httpPort <port>

show ns param

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The Bottom Line

This comprehensive guide illuminates the inner workings of load balancing using the NetScaler appliance. It details how client requests are efficiently managed, from directing requests to a virtual server and distributing them among application servers using predefined algorithms. The setup’s topology positions the load balancing server as a crucial intermediary between clients and the server farm. Diverse virtual server types, wildcard configurations, and firewall setups demonstrate load balancing’s adaptability. Understanding wildcard usage for dynamic traffic handling and the appliance’s search sequence for virtual servers clarifies its operational nuances. Additionally, configuring global HTTP ports enhances traffic management. Ultimately, this knowledge empowers network administrators to fine-tune configurations for optimal traffic distribution, ensuring seamless connectivity and improved network performance.

Frequently Asked Questions

What Is Load Balancing Method in NetScaler?

NetScaler’s load balancing method allocates incoming traffic across servers. Methods like Least Connection, Round Robin, and Source IP Hash distribute load based on criteria like connections, rotation, or client IP, optimizing performance and resource usage for different needs.

What Is the Purpose of Load Balancing?

The primary purpose of load balancing is to evenly distribute incoming network traffic across multiple servers or resources. This aims to optimize resource utilization, prevent individual servers from being overwhelmed by traffic, ensure high availability, minimize downtime, and enhance overall system performance and reliability. By evenly spreading the workload, load balancing helps maintain system stability and provides a seamless user experience even during periods of high demand.