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In 2014, the release of OpenStack Icehouse slated several hypervisors for deprecation. Generally speaking, deprecation means that drivers for the corresponding hypervisors will be removed. In this case, that includes Ironic -- a bare-metal driver -- Docker and Linux Containers, which relies on libvirt, because the drivers that supported these hypervisors were often problematic.
Drivers are tested and evaluated
Leading up to the OpenStack Icehouse release, hypervisor drivers had to meet specific requirements in tests and evaluations in order to ensure a minimum level of feature support for OpenStack. There are three categories of driver testing for OpenStack's compute module. Group A drivers are fully tested and supported; they include libvirt for hypervisors like Kernel-based Virtual Machine and QEMU on x86 platforms. Group B drivers offer some level of testing but might not be fully tested or supported. These drivers include Hyper-V, VMware, XenServer and Xen using libvirt. Group C drivers have limited testing and present possible problems or unreliable behavior. Bare-metal Ironic, Docker and Linux Containers -- through libvirt -- drivers fell into Group C, and OpenStack Icehouse slated them for deprecation.
Since OpenStack Icehouse, however, it doesn't appear that any other hypervisors have been deprecated -- or are scheduled for deprecation -- in any currently maintained Newton, Ocata or Pike releases, nor does there appear to be any additional hypervisor deprecation slated for the OpenStack Queens release that's in development. The current support matrix for OpenStack lists a comprehensive suite of hypervisor drivers, though many features and functions remain optional or missing.
Cloud frameworks need to be flexible
The integration and interoperation between cloud software and hypervisors underscore a potential vulnerability for private cloud deployments. Cloud software doesn't handle virtualization, so private cloud frameworks, like OpenStack, need to work well with numerous hypervisors to become mainstream. Hypervisors aren't supported equally, and aspects like hypervisor features, performance and even long-term inclusion in the cloud software's roadmap aren't assured. The onus is on enterprise adopters to closely follow the evolution of cloud software and their chosen hypervisors and to test each new release before they commit changes to production environments.
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