As a cloud framework, OpenStack must perform a wide variety of functions that depend on interactions and responses from the hypervisor. For example, the guest instance status feature provides real-time details about the power state of the guest VM instance, while the attach block volume to instance feature allows block storage to be dynamically added to a running VM instance. You have to keep in mind, however, that OpenStack hypervisors are different, and not every hypervisor supports every OpenStack feature in the same way -- if at all.
Mandatory features of OpenStack hypervisors
In order to address the differences between OpenStack hypervisors, some features are mandatory, and others are optional. All included OpenStack hypervisors must support a mandatory feature. For example, the guest instance status feature is mandatory, and every hypervisor supports it, while the attach block volume to instance feature is optional and Ironic, Linux Containers and Virtuozzo CT don't support it. By comparison, the auto configure disk feature that allows disk partitioning and resizing is optional, and XenServer is the only platform that supports it. Most OpenStack features and functionality are currently optional.
It's worth noting that a limited stable of mandatory features generally doesn't impair the overall utility of the private cloud platform. Early implementations of Amazon Elastic Compute Cloud instances offered a relatively limited feature set, yet EC2 enjoyed broad adoption. Potential adopters should make the effort to review the feature sets for OpenStack hypervisors and examine whether a desired hypervisor supports valuable features. This is part of the due diligence evaluation and testing of a private cloud implementation. In addition, some features might become mandatory as OpenStack Nova and the suite of available hypervisors continue to mature over time.
Everything you need to know about OpenStack hypervisor support
Hypervisor support is critical in order to ensure interoperability in a private cloud environment. Carefully evaluate and test the variety of supported hypervisors that are available, and be aware of hypervisors that are scheduled for deprecation.
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