Xen Project Partnership Laid Groundwork for CentOS Variants

The Xen Project community today announced it will be a founding project in the CentOS Project‘s new virtualization special interest group (Virt SIG).  The open source hypervisor, a Linux Foundation collaborative project, will thus play a pivotal role in shaping the direction of virtualization support and innovation on top of the CentOS Linux enterprise distribution, as well as help to field test the new governance model for future SIGs.

When the CentOS Project joined forces with Red Hat in January, project leaders promised to open up the distribution to more community contributions. Under the new community model, CentOS will continue to rebuild Red Hat Enterprise Linux. But SIGs, which include independent groups of open source projects, will be invited to build and maintain their own CentOS integrations on top of the core code, or to replace it altogether.  

The first CentOS Project SIG, a partnership with Ceph and GlusterFS focused on storage, kicked off in early April. And the project is planning others. The virtualization group, chaired by Xen Project’s Lars Kurth, is now one of several official SIGs and is open to developers contributing to any server virtualization technology.

“In the past (before Red Hat), there would have never been direct access to the CentOS infrastructure from outside the project itself,” said Karanbir Singh, CentOS Project leader who now works at Red Hat. “As a SIG, we can work with the Xen Project to request resources from the project, and expand the scope of what we’re doing to include hypervisors, containers, storage interfaces and maybe even build a trimmed down kernel customized for virtualized environments.”

Xen-CentOS Project History

Cross-project collaboration is not new territory for the CentOS Project. Perhaps the most successful example has been their work with the Xen Project, said Karsten Wade, CentOS engineering team manager at Red Hat, in his presentation at Collaboration Summit in March.

Over the past two years the Xen and CentOS projects have worked together on the Xen4CentOS project, which issued its first release last July. The relationship forged between them has laid the groundwork for the new SIG model and was a key factor in the decision for the CentOS Project to join Red Hat in the first place.

“The success with Xen definitely contributed to the decision to join Red Hat,” Singh said. “In conversations with Red Hat, Xen used to come up a lot.”

Back in 2008, CentOS Linux was one of the first distributions to have a stable Xen hypervisor implementation and was on the forefront of virtualization staged on Linux, said Singh. That was true until a couple of years ago when CentOS Project maintainers decided not to continue Xen support.  

“A lot of Xen users got stuck on CentOS 5,” said Kurth, chairman of the Xen Project Advisory Board. “We asked if we could provide a migration path to move from 5 to 6, so we worked with KB (Singh) and a few others to kick off Xen4CentOS 6, which is basically a precursor of a CentOS variant.”

Citrix was already using CentOS 6 with a modified kernel as part of the Xen Server, so the projects used that as the baseline to build Xen4CentOS 6, Kurth said.

The partnership has since continued to evolve and laid the groundwork for what is now being called a CentOS variant – code that lives within the CentOS repository and is developed and overseen by a SIG. Xen Project is one of the first to form a SIG and will be working to bring other open source projects into the virtualization SIG.

The idea is to build on the Xen Project’s success and traction in the market to help bootstrap support for other virtualization projects and build a common platform from which to consume the various virtualization technologies on CentOS.

Xen Project Benefits

The CentOS Project will model the SIG governance structure on Apache Foundation’s satellite project approach after their positive experience working with the Xen Project team in 2013. The project has been able to maintain its independence while also working with CentOS developers to release the Xen4CEntOS6 package in a way that was still very easy for users to consume, Singh said.

“This is the exact model we’re trying to follow,” Red Hat’s Wade said. SIGs will be independent, following their own build and release schedules and may even maintain their own kernels, he said.

For its part, the Xen Project team is looking to expand its network of users and developers beyond the community distributions it’s already working with, including OpenSuSE, Debian, Ubuntu, Fedora, Arch Linux, and the Berkeley Software Distribution.

As it stands now, users must be more technically adept to install and support the Xen hypervisor on CentOS. That limits the Xen user base to large companies such as Amazon that have sufficient IT resources, or individual users who download the source code and set it up themselves, said George Dunlap, a senior engineer at Citrix and the maintainer of the kernel scheduler subsystem on the Xen Project.

“Most people want to type yum install Xen and have it just work,” Dunlap said. “So having good distribution support is critical to having a wide number of users in the cloud. And that’s part of the network effect that will bring more users and contributors. CentOS Linux is an important distribution from that respect.”