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When there are two or more geographically dispersed ECS sites within a replication group, a mechanism to load balance across the nodes between sites is recommended. This is especially pertinent in three or more sites where it becomes key for taking advantage of ECS storage efficiency achieved using the ECS XOR feature. Another advantage is when one site is unavailable; requests are automatically forwarded to the surviving site(s), providing disaster recovery and high availability. Global load balancing can be achieved by either using DNS, network routing (that is, OSPF: Open Shortest Path First, BGP: Border Gateway Protocol, and so on), a global server load balancer (GLSB) or a combination of these techniques. Figure 4 provides an example of client requests being sent to a Domain Name System (DNS) which have an entry for a global load balancing mechanism or NGINX. The global load balancing techniques used forwards requests to a pool of NGINX web servers which then forwards requests to a pool of ECS nodes within a replication group.
When considering a global load balancing mechanism, it is important to understand that a read to ECS involves checking with the owner of the object to validate if it has the latest copy locally. If data is not local or in the site cache, it retrieves the data from the site that has the latest version. Thus when architecting a global load balancing solution, it is advised to send or direct the read requests to the owning site if possible. This may depend on the workflow and application.