Cloud Bursting: Gateway Drug for Hybrid Cloud

The first hit’s cheap kid …

Recently Ben Kepes  started a very interesting discussion on cloud bursting by asking whether or not it was real. This led to Christofer Hoff  pointing out that “true” cloud bursting required routing based on business parameters. That needs to be extended to operational parameters, but in general, Hoff’s on the mark in my opinion.

The core of the issue with cloud bursting, however, is not that requests must be magically routed to the cloud in an overflow situation (that seems to be universally accepted as part of the definition), but the presumption that the content must also be dynamically pushed to the cloud as part of the process, i.e. live migration.

If we accept that presumption then cloud bursting is nowhere near reality. Not because live migration can’t be done, but because the time requirement to do so prohibits a successful “just in time” bursting approach. There is already a requirement that provisioning of resources in the cloud as preparation for a bursting event happen well before the event, it’s a predictive, proactive process nor a reactionary one, and the inclusion of live migration as part of the process would likely result in false provisioning events (where content is migrated prematurely based on historical trending which fails to continue and therefore does not result in an overflow situation).

So this leaves us with cloud bursting as a viable architectural solution to scale on-demand only if we pre-position content in the cloud, with the assumption that provisioning is a less time intensive process than migration plus provisioning.

This results in a more permanent, hybrid cloud architecture.


The constraints on the network today force organizations who wish to address their seasonal or periodic need for “overflow” capacity to pre-position the content in demand at a cloud provider. This isn’t as simple as dropping a virtual machine in EC2, it also requires DNS modifications to be made and the implementation of the policy that will ultimately trigger the routing to the cloud campus. Equally important – actually, perhaps more important – is having the process in place that will actually provision the application at the cloud campus.

In other words, the organization is building out the foundation for a hybrid cloud architecture.

But in terms of real usage, the cloud-deployed resources may only be used when overflow capacity is required. So it’s only used periodically. But as its user base grows, so does the need for that capacity and organizations will see those resources provisioned more and more often, until they’re virtually always on.

There’s obviously an inflection point at which the use of cloud-based resources moves out of the realm of “overflow capacity” and into the realm of “capacity”, period.

At that point, the organization is in possession of a full, hybrid cloud implementation.


Some might argue – and I’d almost certainly concede the point – that a cloud bursting model that requires pre-positioning in the first place is a hybrid cloud model and not the original intent of cloud bursting. The only substantive argument I could provide to counter is that cloud bursting focuses more on the use of the resources and not the model by which they are used. It’s the on-again off-again nature of the resources deployed at the cloud campus that make it cloud bursting, not the underlying model.

Regardless, existing limitations on bandwidth force the organization’s hand; there’s virtually no way to avoid implementing what is a foundation for hybrid cloud as a means to execute on a cloud bursting strategy (which is probably a more accurate description of the concept than tying it to a technical implementation, but I’m getting off on a tangent now).

The decision to embark on a cloud bursting initiative, therefore, should be made with the foresight that it requires essentially the same effort and investment as a hybrid cloud strategy. Recognizing that up front enables a broader set of options for using those cloud campus resources, particularly the ability to leverage them as true “utility” computing, rather than an application-specific (i.e. dedicated) set of resources. Because of the requirement to integrate and automate to achieve either model, organizations can architect both with an eye toward future integration needs – such as those surrounding identity management, which continues to balloon as a source of concern for those focusing in on SaaS and PaaS integration.

Whether or not we’ll solve the issues with live migration as a barrier to “true” cloud bursting remains to be seen. As we’ve never managed to adequately solve the database replication issue (aside from accepting eventual consistency as reality), however, it seems likely that a “true” cloud bursting implementation may never be possible for organizations who aren’t mainlining the Internet backbone.

Published Mar 26, 2012
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