Load Balancing

  Load Balancing

• A feature of a Load Balancer that balances the load among separately managed servers that deliver the same applications or host the same data.

Load balancing allows an server administrator to distribute the client requests across multiple servers to optimize resource utilization. Load balancing improves server fault tolerance and end-user response time by distributing load across servers, and directing traffic away from unavailable servers.

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. Load balancing algorithms are used to prevent bottlenecks by forwarding the client requests to the servers best suited to handle them. Thus, balancing the load on the servers.

A load balancing setup includes a virtual server (vserver) used to proxy multiple servers in a server farm and balance the load among them. The vserver identifies the server using the load balancing criteria and directs incoming client requests to it. 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.

Load balancing traffic management is most commonly used for traffic management for Layer 4 TCP and UDP through layer 7 FTP, HTTP and HTTPS. Other protocols can be load balanced as well.

Load balancing uses a number of algorithms, called Load Balancing Methods, to determine how to distribute the load among servers. Common load balancing (LB) methods include "Least Connections Method" and "Round Robin".

Entities that are commonly found inside of a load balancer are:

Vserver - An entity that is represented by using an IP Address, a Port and Protocol. The Client sends connection requests to this IP Address. The Vserver represents a bank or farm of servers. The vserver can use an Internet Protocol version 4 (IPv4) or an Internet Protocol version 6 (IPv6) address, and the server object can represent a server with either an IPv4 or IPv6 address. Load balancing allows for configurations in which the vserver and the server use
different IP address types.

VIP - The VServer IP (VIP) Address is usually a public IP Address, and is the address to which all cients connect using a web browser or other software.

Service - An entity that is represented by using a IP Address, a Port and Protocol. A Service is a login representation of a server or an application running on a server. The Service or Services are bound to the VServer to create a logical flow of data from Client <=> Vserver <=> Service <=> Server.

Server Object - An entity that is represented by using a IP Address. The server object is usually created when you create a service. The IP Address of the service is taken as the name of the server object. It is also possible to create a server object using an ASCII name and then create services by using the server object.

Monitor - An entity that tracks the health of the services - an integral part of determining load and how to balance traffic amoung servers. The load balancer periodically probes the servers using the monitor bound to each service. If a server does not respond within a specific response time-out, and the specified numbers of probes fails, the service is marked DOWN. The load balancer then performs load balancing amoung the remaining services.

Persistence - Load balancing allows for the use of Persistence, where you enable persistent connections between clients and servers. This is especially useful in e-commerce applications such as shopping cart usage, where the server needs to maintain the state of the connection to track the transaction, and make sure the data makes it back to the server handling the transaction.

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