Implementing Load Balancing

Load balancing is the process by which server workload is spread among two or more server computers to prevent overload on a single server. With load balancing, a client makes a request for work as if a single server is involved; instead, more than one server can handle the request for the client.

There are two types of load balancing: static and dynamic, compared as follows:

• In static load balancing, a client always goes to the same server for tasks. The server that handles a client's requests is hard coded at the client site. Load balancing can be controlled by changing settings on the client machine or by routing new clients to new servers.
  
  With static load balancing, if a particular server is unavailable, the clients using that server cannot continue to work unless they are reconfigured to point to an available server.

• With dynamic load balancing, each time a client requests server-side work, a different server can handle the task. When the client makes a request, that request goes to a referral server, which in turn redirects the request to a server that can handle the workload.
  
  The referral server monitors the workload of each server and balances work requests based on the workload. With dynamic load balancing, if one server becomes available, clients do not have to be reconfigured. The referral server handles redirection of requests.

Load balancing decisions therefore have the following design implications for software solutions:

• Performance can be better with static load balancing, because requests do not have to be routed through a referral server.

• Availability can be better with dynamic load balancing, because if a server is unavailable, its requests are just shifted to another server that is available. With static load balancing, if a server becomes unavailable, the clients must be reconfigured to point to a different server.

• Scalability can be better with dynamic load balancing, because the referral server will automatically allocate requests depending on available resources.

In conclusion, if your system will be extremely stable, with little change anticipated in its configuration or scale and with highly dependable servers, static load balancing might be an option, because it would provide a performance advantage.

If the system needs to scale in the foreseeable future, or if there are factors that affect dependability or servers or server configuration, however, dynamic load balancing should be your choice.