For a while now, I’ve been talking to Gartner clients about what concerns keep them off public cloud infrastructure, and the diminishing differences between private and public cloud from service providers. I’ve been testing a thesis with our clients for some time, and I’ve been talking to people here at Gartner’s data center conference about it, as well.

That thesis is this: People will share a data center network, as long as there is reasonable isolation of their traffic, and they are able to get private non-Internet connectivity, and there is a performance SLA. People will share storage, as long as there is reasonable assurance that nobody else can get at their data, which can be handled via encryption of the storage at rest and in flight, perhaps in conjunction with other logical separation mechanisms, and again, there needs to be a performance SLA. But people are worried about hypervisor security, and don’t want to share compute. Therefore, you can meet most requirements for private cloud functionality by offering temporarily dedicated compute resources.

Affinity rules in provisioning can address this very easily. Simply put, the service provider could potentially maintain a general pool of public cloud compute capacity — but set a rule for ‘psuedo-private cloud’ customers that says that if a VM is provisioned on a particular physical server for customer X, then that physical server can only be used to provision more VMs for customer X. (Once those VMs are de-provisioned, the hardware becomes part of the general pool again.) For a typical customer who has a reasonable number of VMs (most non-startups have dozens, usually hundreds, of VMs), the wasted capacity is minimal, especially if live VM migration techniques are used to optimize the utilization of the physical servers — and therefore the additional price uplift for this should be modest.

That gets you public cloud compute scale, while still assuaging customer fears about server security. (Interestingly, Amazon salespeople sometimes tell prospects that you can use Amazon as a private cloud — you just have to use only the largest instances, which eat the resources of the full physical server.)