Relationship To Failover
Load balancing is often used to implement failover — the continuation of a service after the failure of one or more of its components. The components are monitored continually (e.g., web servers may be monitored by fetching known pages), and when one becomes non-responsive, the load balancer is informed and no longer sends traffic to it. And when a component comes back on line, the load balancer begins to route traffic to it again. For this to work, there must be at least one component in excess of the service's capacity. This can be much less expensive and more flexible than failover approaches where a single live component is paired with a single backup component that takes over in the event of a failure. Some types of RAID systems can also utilize hot spare for a similar effect.
Read more about this topic: Load Balancing (computing)
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