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To manage a CloudStack VM properly, current CloudStack has hypervisor resource-agent to participate VM lifecycle state management and periodically sync-back with CloudStack management server. Therefore, in addition for hypervisor resource agent to be aware of hypervisor specific VM power state, it needs also to know about VM's state the states introduced in CloudStack, especially to those transitional CloudStack VM states like Starting, Migrating, etc.

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 "Full-sync" and "delta-sync" are currently forming the foundation of VMSync process in CloudStack. Although it works nicely most of time , as CloudStack adds support to external managers like for VMs that are solely operated by CloudStack, as soon as the introduction of external VM managers are involved, for example Citrix XenCenter, VMware vCenter, the state sync scenarios can become hard to handle when out-of-band changes posted from external managers, following use cases sometimes can cause problematic issues in during normal operations of CloudStack operating time.

1) Takes a long time to bring up all hypervisor hosts in a large setup

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This improvement effort is to address these issues, it will help CloudStack to better interage with third-party virtualization managers like VMware vCenter to perform HA, DRS, FT etc better and reliable reliably through CloudStack.

Design

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