Interoperability between clouds requires more than just VM portability

The issue of application state and connection management is one often discussed in the context of cloud computing and virtualized architectures. That's because the stress placed on existing static infrastructure due to the potentially rapid rate of change associated with dynamic application provisioning is enormous and, as is often pointed out, existing "infrastructure 1.0" systems are generally incapable of reacting in a timely fashion to such changes occurring in real-time.

The most basic of concerns continues to revolve around IP address management. This is a favorite topic of Greg Ness at Infrastructure 2.0 and has been subsequently addressed in a variety of articles and blogs since the concepts of cloud computing and virtualization have gained momentum. The Burton Group has addressed this issue with regards to interoperability in a recent post, positing that perhaps changes are needed (agreed) to support emerging data center models. What is interesting is that the blog supports the notion of modifying existing core infrastructure standards (IP) to support the dynamic nature of these new models and also posits that interoperability is essentially enabled simply by virtual machine portability.

From The Burton Group's "What does the Cloud Need? Standards for Infrastructure as a Service"

First question is: How do we migrate between clouds? If we're talking System Infrastructure as a Service, then what happens when I try to migrate a virtual machine (VM) between my internal cloud running ESX (say I'm running VDC-OS) and a cloud provider who is running XenServer (running Citrix C3)? Are my cloud vendor choices limited to those vendors that match my internal cloud infrastructure? Well, while its probably a good idea, there are published standards out there that might help. Open Virtualization Format (OVF) is a meta-data format used to describe VMs in standard terms. While the format of the VM is different, the meta-data in OVF can be used to facilitate VM conversion from one format to other, thereby enabling interoperability.

...

Another biggie is application state and connection management. When I move a workload from one location to another, the application has made some assumptions about where external resources are and how to get to them. The IP address the application or OS use to resolve DNS names probably isn't valid now that the VM has moved to a completely different location. That's where Locator ID Separation Protocol (LISP -- another overloaded acronym) steps in. The idea with LISP is to add fields to the IP header so that packets can be redirected to the correct location. The "ID" and and "locator" are separated so that the packet with the "ID" can be sent to the "locator" for address resolution. The "locator" can change the final address dynamically, allowing the source application or OS to change locations as long as they can reach the "locator". [emphasis added]

If LISP sounds eerily familiar to some of you, it should. It's the same basic premise behind UDDI and the process of dynamically discovering the "location" of service end-points in a service-based architecture. Not exactly the same, but the core concepts are the same. The most pressing issue with proposing LISP as a solution is that it focuses only on the problems associated with moving workloads from one location to another with the assumption that the new location is, essentially, a physically disparate data center, and not simply a new location within the same data center; an issue with LISP does not even consider. That it also ignores other application networking infrastructure that requires the same information - that is, the new location of the application or resource - is also disconcerting but not a roadblock, it's merely a speed-bump in the road to implementation.

We'll come back to that later; first let's examine the emphasized statement that seems to imply that simply migrating a virtual image from one provider to another equates to interoperability between clouds - specifically IaaS clouds. I'm sure the author didn't mean to imply that it's that simple; that all you need is to be able to migrate virtual images from one system to another. I'm sure there's more to it, or at least I'm hopeful that this concept was expressed so simply in the interests of brevity rather than completeness because there's a lot more to porting any application from one environment to another than just the application itself.

Applications, and therefore virtual images containing applications, are not islands. They are not capable of doing anything without a supporting infrastructure - application and network - and some of that infrastructure is necessarily configured in such a way as to be peculiar to the application - and vice-versa.

We call it an "ecosystem" for a reason; because there's a symbiotic relationship between applications and their supporting infrastructure that, when separated, degrades or even destroys the usability of that application. One cannot simply move a virtual machine from one location to another, regardless of the interoperability of virtualization infrastructure, and expect things to magically work unless all of the required supporting infrastructure has also been migrated as seamlessly. And this infrastructure isn't just hardware and network infrastructure; authentication and security systems, too, are an integral part of an application deployment.

Even if all the necessary components were themselves virtualized (and I am not suggesting this should be the case at all) simply porting the virtual instances from one location to another is not enough to assure interoperability as the components must be able to collaborate, which requires connectivity information. Which brings us back to the problems associated with LISP and its focus on external discovery and location.

There's just a lot more to interoperability than pushing around virtual images regardless of what those images contain: application, data, identity, security, or networking. Portability between virtual images is a good start, but it certainly isn't going to provide the interoperability necessary to ensure the seamless transition from one IaaS cloud environment to another.

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Published Feb 10, 2009

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cloud computing infrastructure