Amazon Web Services was (AFAIK) one of the first products that introduced availability zones – islands of infrastructure that are isolated enough from each other to stop the propagation of failure or outage across their boundaries.
Not surprisingly, multiple availability zones shouldn’t rely on a central controller (as Amazon found out a few years back), and there are only few SDN controller vendors that are flexible enough to meet this requirement. For more details, watch the free Availability Zones video on my web site (part of Scaling Overlay Virtual Networking webinar).
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