What is an “Availability Zone” in Eucalyptus?
Amazon implements “availability zones” to allow users some degree of control over instance placement. Specifically, EC2 users can choose to host images in different availability zones if they wish to try and ensure independent failure probabilities. Amazon, presumably, takes steps to insulate instances in separate availability zones from correlated failure (e.g., a single power outage that takes out a data center). Under Eucalyptus, the abstraction is slightly different. Each availability zone corresponds to a separate cluster within the Eucalyptus cloud. The advantage is that the networking within a single availability zone can be made much faster (i.e., it uses the cluster’s private network in native mode). For allocations that span clusters, the technology Eucalyptus uses to implement a private network for each allocation imposes a substantial performance penalty. Thus the two are similar in that cloud allocations to separate availability zones do reduce the chance of correlated fai
