Free Load Balancer Software for powering your Business Growth

A load balancer is a network appliance responsible for the effective distribution of incoming network traffic across multiple backend servers in order to guarantee always-available application services. Load balancers can be deployed as software appliances, hardware appliances or even as a service. A load balancer allows you to optimise server utilisation and remove single points of failure in application delivery to guarantee the following: 

Resilience – A load balancer allows you to run multiple application servers to fulfil the same role. In the event of a server failure, the load balancer will detect this and redirect traffic to the remaining online, healthy servers. This ensures high availability and reliability for applications. 

Scalability – Load balancers allow you to seamlessly scale services without impacting performance. By simply adding more servers behind the load balancer for distribution, you introduce the ability to adapt to an increase in load. 

Capacity – To increase capacity simply add more servers behind the load balancer. (Ok it’s not normally as easy as that because you’ll probably have databases and other app servers to consider, but you get the idea)

Load balancers distribute application traffic based on many different load balancing strategies or load balancing policies as they are sometimes called. To determine if a back-end server is online and healthy, a load balancer will use back-end server monitoring and Server health checking. The principles of load balancing have been around for many years, but load balancers have evolved significantly from the basic layer 4 device to much more sophisticated layer 7 Application Delivery Controllers, or ADCs, as Gartner refers to them. ADCs offer many additional key features, including security and traffic management.

A load balancing strategy or policy instructs the load balancer on where to send the next incoming request. There are many load balancing strategies available depending on the specific solution. However, a few common ones are listed below: 

Round Robin: The most simple load balancing method where each server takes turns receiving a request. 

Least Number of Connections: The load balancer will keep track of the number of connections a server currently has and send the next request to the server with the least connections. Note: Older, layer 4 only load balancers tend not to support this as they typically run DSR (Direct Server Return) and don’t know how many connections are currently on the back-end servers. 

Weighted: Typically, servers are allocated a percentage capability as one server could be twice as powerful as another. Weighted methods are useful if the load balancer does not know the real and actual performance of the server. 

Fastest Response Time: This load balancing method is normally only available on more advanced products, and the request will be sent to the fastest responding server.

Persistence is a feature that is required by many web applications and websites. Once a user has interacted with a particular server, all subsequent requests are sent to the same server, thus ‘persisting’ to that specific server. Session persistence ensures a continuity of service and a seamless end-user experience and is often a requirement of e-commerce applications whose session state is stored on the local webserver instead of a shared database. Persistence can come in many forms:

Load Balancer Cookie: The load balancer will set a cookie at the client and use this to identify the back-end server for this user. 

Application Session Cookies: Many application servers already set their session ID, such as JSP or Asp.net session cookie. You can configure the load balancer to use these. 

IP Based: Uses the Client IP address to persist. This method works for layer 4 and layer 7.

SSL Session: Uses the SSL session ID. This method is not very common as the session ID can change, and persistence could be lost. 

RDP Session Cookie: Used for RDP connections.