Why do you need to load balance ?
Here i will put forward the various options available for web load balancing.
Before we go into that , let us first examine why do we need load balancing after all.Consider you develop a website and is available to the public.If the application is served from a single webserver then there is a high chance that the machine will be overwhelmed if the usage of the application increases. This may result in users experiancing unusually high response times or in worse case the machine can come to a halt.So you need some mechanism to distribute the load across different machines,without the client having to swich address.
There are many widely used approaches. The most common ones are
- DNS based load balancing
- Software load balancing
- Hardware load balancing
DNS based Load Balancing
Here the DNS server is configured in such a way that it returns different IP addresses for various requests to the DNS server for a particular domain name.
The DNS server may contain say 5 IPs for a particular domain name and on a round robin basis it can different IPs for different requests. The draaw back with this approach is it cannot do a weight based routing as it has no information on which server is heavily loaded. It can only do a round robin based load balancing. This would be sufficient for many websites.
Software Load Balancing
In this mechanism another webserver or some software plugins does the load balancing.
In the case of weblogic many plugins are available for various web servers. WLProxy plugin from weblogic is available for IIS, Apache etc. This plugin can load balance the web requests if the web application is deployed in a cluster in a weblogic server. The advantage with software load balancing is that it can do weigh based load balancing also. It can detect if any server in the cluster has go down . The plugin can remove that address from its algorithm. Also it can do server affiinity.
Hardware load balancing
In this mechanism a hardware like F5 Big IP load balancer can be used to do the load balancing.Hardware load balancers has mechanisms to load balance SSL requests also.
Also many such load balancers has the capability to compress a response. This can result in good response time from a low bandwidth environment.
Which load balancer to use is a decision to be taken based on the specific application requirements and projected usage.
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