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Lori MacVittie

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The Colonial Data Center and Virtualization

Colonial as in corals and weeds and virtual machines

No, not colonial as in Battlestar Gallactica or the British Empire, colonial as in corals and weeds and virtual machines

I was out pulling weeds this summer – Canada thistle to be exact – and was struck by how much its root system reminded me of Cnidaria (soft corals to those of you whose experience with aquaria remains relegated to suicidal goldfish).  Canada thistle is difficult to control because of its extensive root system. Pulling a larger specimen you often find yourself pulling up its root, only to find it connected to three, four or more other specimens. Cnidaria reproduce in a similar fashion, sharing a “root” system that enables them to share resources. Unlike thistles, however, Cnidaria has several different growth forms. There’s a traditional colonial form that resembles thistles – a single, shared long root with various specimens popping up along the path – and one that may be familiar to folks who’ve seen Finding Nemo: a tree formation in which the root branches not only horizontally but vertically, with individual specimens forming upwards along the branch in what gives it a tree-like appearance. cnidaria vms

360px-Cnidaria_polyp_tree_colony_01Cnidaria produce a variety of colonial forms, each of which is one organism but consists of polyp-like zooids. The simplest is a connecting tunnel that runs over the substrate (rock or seabed) and from which single zooids sprout. In some cases the tunnels form visible webs, and in others they are enclosed in a fleshy mat. More complex forms are also based on connecting tunnels but produce "tree-like" groups of zooids. The "trees" may be formed either by a central zooid that functions as a "trunk" with later zooids growing to the sides as "branches", or in a zig-zag shape as a succession of zooids, each of which grows to full size and then produces a single bud at an angle to itself. In many cases the connecting tunnels and the "stems" are covered in periderm, a protective layer of chitin.[6] Some colonial forms have other specialized types of zooid, for example, to pump water through their tunnels.[12]

-- Wikipedia, Cnidaria

Of course, both thistle and Cnidaria and the notion of colonial inter-dependence is one that’s shared by the data center.


Virtual machines deployed on the same physical host replicate in many ways the advantages and disadvantages of a Cnidarian tree-formation. The close proximity of the 15.6 average VMs per host (according to Vkernel VMI 2012) allows them to share the “local” (virtual) network, which eliminates many of the physical sources of network latency that occur naturally in the data center. But it also means that a failure in the physical network connecting them to the network backbone is catastrophic for all VMs on a given host. Which is why you want to pay careful attention to placement of VMs in a dynamic data center.

The concept of pulling compute resources from anywhere in the data center to support scalability on-demand is a tantalizing one, but doing so can have disastrous results in the event of a catastrophic failure in the network. Architecture and careful planning is necessary to ensure that resources do not end up grouped in such a way that a failure in one negatively impacts the entire application. Proximity must be considered as part of a fault isolation strategy, which is a requirement when resources are loosely – if at all – coupled to specific locations within the data center.

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Lori MacVittie is responsible for education and evangelism of application services available across F5’s entire product suite. Her role includes authorship of technical materials and participation in a number of community-based forums and industry standards organizations, among other efforts. MacVittie has extensive programming experience as an application architect, as well as network and systems development and administration expertise. Prior to joining F5, MacVittie was an award-winning Senior Technology Editor at Network Computing Magazine, where she conducted product research and evaluation focused on integration with application and network architectures, and authored articles on a variety of topics aimed at IT professionals. Her most recent area of focus included SOA-related products and architectures. She holds a B.S. in Information and Computing Science from the University of Wisconsin at Green Bay, and an M.S. in Computer Science from Nova Southeastern University.