Xen is a familiar name to most in the Linux community, not least because of its transformation into a Linux Foundation Collaborative Project earlier this year. The hypervisor technology has thrived for the past 10 years, offering a stable, well-tested choice for virtualization that's been adopted by the likes of Amazon and Rackspace, to name just two examples.
Back in 2010, however, the Xen Project suffered a blow when Red Hat dropped Xen in favor of KVM for Red Hat Enterprise Linux (RHEL) 6, thereby leaving users of RHEL-based CentOS in the cold as well. "This has been quite painful for Xen users; CentOS has been and still is one of the most popular Linux distros for Xen users," explained Lars Kurth, Xen community manager for Citrix, a key sponsor of the technology. "The consequence of Xen having been removed from CentOS 6 was that Xen and CentOS 5 users had no upgrade path."
Well, Thursday brought good news for those on both sides of the problem thanks to the launch of Xen4CentOS, which has brought CentOS integration back to Xen at last.
The Xen4CentOS project is a collaborative effort between the Xen Project, the Citrix Xen open source development teams, the CentOS team, the GoDaddy Cloud operations group and Rackspace Hosting to package, deliver and maintain a stable Xen hypervisor and its related tooling for CentOS 6. Specifically, it enables CentOS 6/x86_64 to be used as a Dom0 base platform to host Xen in paravirtual (PV) and full virtualization (HVM) deployment modes.
"The goals of the Xen4CentOS project were to ensure that existing tooling that users have in production will continue to work," Kurth told Linux.com. "However, support for the newer Xenlight layers and the XL command line tools are also provided."
Most libvirt functions continue to work on Xen4CentOS6 as they did on Xen3CentOS5, enabling users to easily migrate their infrastructure over from CentOS 5 to 6, he noted.
"A second primary principle the project was working against was to build and deliver a Linux kernel based on the 3.4 LTS release," Kurth added. "This has been stabilized through extensive testing in production environments, with enhanced Xen support as recommended by the Xen development team."
'They Now Have an Upgrade Path'
Choice and freedom are both important aspects of open source software, said James Bulpin, director for open source engineering at Citrix and the Citrix rep on the Xen Project Advisory Board. "I’m very happy to see the CentOS community working collaboratively with the Xen community to get Xen into their 6.x releases and give choice and freedom back to their users."
It's an important move for the large number of Xen users currently stuck on CentOS 5.x, Bulpin told Linux.com -- "they now have an upgrade path that will allow them to retain their preferred Linux distribution and to continue to use their choice of hypervisor."
As an active member of the Xen Project, Citrix has helped CentOS create and maintain Xen packages by leveraging its investment and capabilities in using Xen in products for enterprise, SMB and cloud deployments. Citrix will continue to work with the CentOS community to maintain the CentOS 6.x Xen packages, Bulpin said.
Challenges Along the Way
There were some challenges in making Xen4CentOS happen, Kurth admitted. For example, "Xen requires a newer Linux kernel (newer than 3.0), so we dropped a 3.4 kernel into CentOS 6, did some packaging and tuning," he explained. The participation of Citrix, GoDaddy and Rackspace helped toward that end, he added.
The benefits are many, however. Not only will CentOS users of Xen now get the latest features of Xen 4.2 and CentOS 6.4, but "a side-effect of using the 3.4 LTS kernel in CentOS 6 includes improved power efficiency, performance and driver support," Kurth pointed out. "This should make Xen with CentOS an excellent option for virtualization."
'A Huge Gain'
CentOS and Xen both play an important role at GoDaddy, Darren Shepherd, cloud architect for the firm, told Linux.com.
"Unfortunately, in the past we had to treat CentOS and Xen servers as different entities that had to be operationalized within our company," Shepherd explained. "This means different ways of monitoring, deploying and patching. Additionally, the engineers supporting these systems had to have different skill sets."
Now, with Xen packaging in CentOS, "we can consolidate those efforts," he added. "For most practical purposes, Xen can be treated as just another rpm on the server. This is a huge gain for us from the operations perspective: How we manage Xen servers can now fall in line with the expertise we already have in running very large CentOS deployments."
Last but not least, another key benefit of the Xen4CentOS project has been to bring together Xen users and the Xen developer community to solve real problems that exist in the Linux user community today, Kurth pointed out.
"The project has also increased understanding of the type of issues that Linux distributions face," he explained. "This is significant, because it will allow Xen developers to work better with Linux distributions in future, which aligns well with the Xen Project's goal to work more closely with the Linux ecosystem as well as other downstreams."
Looking ahead, "we hope that this will lead to more projects of this type going forward," he concluded. "This also shows what the Xen Project can deliver as part of the Linux Foundation."
A quick-start guide is now available for Xen4CentOS on the CentOS Wiki.