Server virtualization comprises of both hypervisor and container technologies, with the former currently attracting more enterprise buy-in. However, with mid-market organizations virtualizing their infrastructure for the first time and looking to public cloud vendors to augment existing IT capabilities, there may be room for virtualized containers to grow, observers note.
Errol Rasit, principal analyst at Gartner, explained that both hypervisors and containers, also known as shared operating system (OS) virtualization, are defined as server virtualization technologies but are fundamentally different with unique benefits and supported by different software vendors.
Virtualized containers serve up virtual images delivered within the OS as multiple partitions, or "containers", Rasit said. On the other hand, a hypervisor is a thin layer of software that sits below the OS layer and is used to manage multiple OS images, he added.
Elaborating on this, Jan-Jaap Jager, vice president and Asia-Pacific general manager at Parallels, added that the key difference between both technologies is that virtualized containers all share the same OS, or kernel, whereas hypervisors do not.
Weighing up the pros and cons of virtualized containers, he said the key advantage is that it makes sharing of information and resources easy. "Since the containers share the same kernel, page sharing is almost automatic. Comparatively, hypervisors make sharing cumbersome and not interoperable between operating systems."
Jager added that if the partitioning of virtualized containers is done correctly, it is possible to pack up to three times the density of virtual machines onto the system compared with a hypervisor-based system.
The flipside is that hypervisors offer more security and control over one's virtual environment, said Mike Adams, group manager of product marketing infrastructure at VMware. He pointed out that each virtual machine (VM) is "securely isolated" to protect it from unwanted inspection coming from the host machine level or other VMs, and is able to run different flavors of OS according to the company's needs.
The VMs can also be easily ported across different hosting sites with entirely different hardware because the hypervisor layer provides a common platform to every virtual machine, Adams noted.
Evolving virtualization landscape
Currently, the dominant flavor of virtualization technology is hypervisors which account for 70 percent of the global market's server spend, Rasit revealed. Container-based virtualization is mainly utilized on Unix and mainframe systems, and this makes up the remaining 30 percent of investments.
He attributed the large share of hypervisor-based technology adoption to the implementation styles of virtualization providers as most favor this technology, as well as open source alternatives such as Xen and Red Hat's KVM.
That said, the Gartner analyst noted that a "rapidly growing number" of mid-market enterprises are virtualizing their hardware for the first time, and now have several strong alternatives from which to choose. For those looking to sign up for infrastructure-as-a-service offerings (IaaS) or deploy private cloud computing, he suggested that container-based virtualization technology is the "foundational element" for these options.
With the growth of cloud computing, Rasit said there is potential for container-based virtualization in x86 machines to grow alongside hypervisor uptake.
"Despite the current hypervisor virtualization lead, there's still room for this market to change as it grows, particularly as the goal for virtualization providers is to compete for the cloud market [which is] a growing opportunity," he said.
Jager said the hosting market is an area where container-based virtualization can flourish, as companies such as Google and Facebook have understood the benefits of the technology and have been using it for a long time.
"Traditional enterprises seem to stick to technology that they can understand easily or are already using, such as hypervisors, and are also less price sensitive," the Parallels executive noted.
"On the other hand, hosting service providers tend to use containers to supply a cheaper and denser version of virtualization to their clients, as these companies are more price- and density-sensitive by nature."