A divide as real as any weather front separates private, wholly owned data centres from public, capacity-for-hire cloud providers. There is a role for IT in creating a bridge across this divide as virtualisation of all types enables more efficient application development, virtual machine provisioning and business continuity.
A bridged private/public cloud promises efficient workload relocation and an evolutionary path to more cost-effective IT operations. However, the challenges to building a bridge between private and public clouds are real. Aside from the emerging nature of cloud computing technology, IT managers must work with developers and business managers to ensure that development platforms, management controls and compliance issues are aligned between the private and public platforms in order to reap these benefits.
Debate Terms
Before covering what can be done with a bridged private/public cloud, I’d like to start with some basic definitions. In May, NIST (National Institute of Standards and Technology) issued a draft publication titled “Cloud Computing Synopsis and Recommendations,” which described the essential characteristics of cloud computing as an on-demand, self-service of resource pools that are rapidly elastic and provided as a measured service. To this I’ll add multitenancy, in the form of segregating traffic from one organisation or business unit from another.
NIST outlines several deployment models. The most important of these cloud infrastructure models are private, operated solely for an organisation either on- or off-premises; public, available to the general public and owned by an organisation selling cloud services; and hybrid, which is a composite of the two. In a hybrid cloud, the public and private compute environments remain unique, but data and applications are portable between them.
The newly formed ODCA (Open Data Center Alliance), an independent consortium of global IT users, also just released its first usage models. These usage models are recommendations from IT users that have a longterm view of data-centre requirements, including one for virtual machine interoperability between different virtualisation platforms and portability between infrastructure providers, which is an essential component in bridging between the private and public clouds.
While there is a debate of epic proportions about the definition of private and public cloud computing, for IT managers the more important questions are when might it make sense to build a bridge between a private and public cloud so that the business gains a competitive edge? And what will it take to integrate on-premises infrastructure with that running in the public cloud?
Why Build a Bridge?
Application development was among the first beneficiaries of x86 server virtualisation and set the stage for running infrastructure on site and in a hosted environment. Setting up test and development environments composed of virtual machines that could be rapidly provisioned and de-provisioned on shared resources was also a driver for using public cloud services including AWS (Amazon Web Services).
Corporate users can use architectural guides today to move workloads from private to public, enterprise-class cloud providers. For example, VMware partners with public cloud infrastructure providers including Bluelock, CSC, Terremark and others using its VMware vCloud Data Center Services.
In this case, the private/public cloud bridge connects infrastructure (usually processing, storage and networks) or platform (which usually adds to this the operating system and database) so that applications can be built using familiar tools. These cloud “as a service” offerings are referred to as IAAS (infrastructure as a service) and PAAS (platform as a service).
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