CloudStack, the project originally created by, then donated to Apache after Citrix acquired it, is now a full-fledged Apache Foundation project, moving up from the incubator and bringing with it plans for a future of hosting private clouds.

CloudStack as a project is strictly focused on building an Infrastructure-as-a-Service platform. This means its primary task is to spin up and manage virtual machines within a cluster. Five years ago, such a system would have been called a data-center operating system, but today the proper term is “IaaS”—or, as it’s referred to in its DevCloud sub-project, “cloud in a box.”

Chip Childers, vice president of CloudStack, said that the project was already quite robust when the Apache Foundation contributed to it more than a year ago. “Our users use it in everything from small lab environments up through some fairly large deployments with as many as 30,000 hosts under management. That’s some pretty big diversity,” he said.

CloudStack has grown from being an entirely Citrix-run effort to being a more broadly supported Apache project, said Childers. Philosophically, the project allows for two models of management for virtual machines.

“Virtual machines are either pets or cattle,” said Childers. The pet model is where a single VM is taken care of and tweaked, typically on the desktop or inside a development system.

“The cattle model is how you would use Amazon Web Services—or other IaaSes—where you can’t guarantee per-host or per-VM availability,” said Childers. Thus, CloudStack can herd large swaths of machines, or be used to properly care for and feed a set of virtual machines.

For developers, that pet model is important because it enables them to spin up virtual machines locally to recreate multi-tiered cloud applications for development and testing purposes.

The cattle model, on the other hand, can actually be applied directly to Amazon Web Services-based systems, thanks to the merging of former project Cloud Bridge with the core CloudStack project. This work took place at Apache, and has allowed for the embedding of AWS-like APIs within a CloudStack cloud.

That merge took place because, as Childers said, “There is a lot of desire for AWS compatibility. Back when existed [as an independent entity], they had a separate product on top of CloudStack called Cloud Bridge, not to be confused with the Citrix product of the same name. It provided an EC2 compatibility layer.

“We took that code and made it core to the project. Now the operator of the cloud can choose to offer EC2 APIs.”

As a full-fledged Apache Foundation project, CloudStack should see major feature releases every four months, said Childers. The team plans to push out bug fixes and stability releases between those four-month cycles as well.