Nimbula, the so-called cloud operating system start-up put in train by a couple of the boys credited with creating Amazon’s EC2 service, has gotten a $15 million B round.

Accel Partners led the check-signing. Sequoia Capital also pulled out a pen. Sequoia and VMware, oddly enough, staked Nimbula to its $5.75 million first round.

Accel, like Sequoia, gets a board seat. VMware’s ex-CEO Diane Greene – in another small world moment – also sits on the board but is not an investor.

The money is supposed to go into developing hybrid cloud computing technologies and pushing out Nimbula’s RESTful HTTP API-based widgetry for managing on- and off-premises infrastructures.

The stuff is now in beta with a few multinationals in financial services, technology and healthcare that have scads of servers.

Nimbula, which came out of stealth mode in June after getting started early last year, is writing a cloud management systems styled Nimbula Director that’s supposed to deliver Amazon EC2-like services behind the firewall.

It’s advertised as blending EC2-like scale, agility and efficiency with private infrastructure customization, security and control by repurposing the data center – well, at least the data center’s preferably 64-bit industry standard gear– while supporting controlled access to off-premise clouds.

Nimbula Director promises to provide utility-grade cloud features like policy-based authorization, secure multi-tenancy, topology-independent distributed network security, dynamic storage provisioning, monitoring and metering. It’ll automate deployment and cloud management to scale and migrate existing applications into the cloud by supporting multi-platform environments and flexible networking and storage.

Nimbula Director installs on bare metal and runs on a single or multi-cluster site made up of a networked collection of x86 computers.

It works by abstracting the underlying technology into a coherent view of a completely automated on-premise compute cloud. The API is the interface. Cloud resources can also be managed via a command line interface (CLI) and web control panel built on top of the API.

Beneath the virtual data center abstraction sits the physical layer of storage, network and compute hardware managed by the multilayer control software. Nimbula integrates a hypervisor, currently KVM or Xen, with node management software on each node to achieve automated deployment and configuration.

It’s supposed to be able to span thousands of server nodes in a single control domain.

Formal launch is expected later this year. By then it may be able to accommodate OVF, the open virtualization format, and VMware import. It converts VM image out-of-band to Nimbula or EC2 images.

The Nimbula team includes co-founder and CEO Chris Pinkham, once VP of engineering at Amazon.com; co-founder and VP of products Willem van Biljon, who led the EC2 development team and in a previous life co-founded Mosaic Software; VP of sales and development Martin Buhr, an ex-Microsoftee who was business development director at Amazon Web Services; and VP of marketing Reza Malekzadeh, VMware’s long-time marketing guy and co-founder of Twingo Systems sold to Cisco.

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