CentOS is a "distribution" with a rather unique description: it is a free (gratis) clone of a commercially-supported "distribution" with all the branding removed. Being enterprise-grade distribution means solid and well-tested; but it also means not having the latest functionality. It also means having a small enough feature set to provide commercial support in a viable manner: and that typically means choosing one technology and sticking with it. But what if you wanted your entire system to be solid, and well-tested, but want the latest features for one particular package or program? Or what if you really wanted an enterprise system, but wanted to use one of the alternate technoligies that were not selected? This is where CentOS SIGs come in. The new CentOS is still at its core a clone of an upstream enterprise distribution. But having had success with the Xen4CentOS project, which provided a version of Xen to run on CentOS 6, they have now generalized the process. This talk will talk about CentOS SIGs: the vision, the structure, what SIGs are available. We will compare and contrast them to other community distro development models like Fedora, OpenSuSE, Debian, Ubuntu, and so forth. We will also share lessons from the CentOS Virt SIG, in which a number of virtualisation and related technologies such as Xen, oVirt, Docker and others collaborate.

1. Lars Kurth (standing in for George Dunlap)
Lead CentOS Virtualization SIG
Community Manger, Xen Project
Chairman, Xen Project Advisory Board lars_kurth

2. Community-oriented distros
Debian, Gentoo, BSDs
Enterprise targeted distros
RedHat, SuSE
Company-sponsored community distros
Fedora, OpenSuSE
Company-patched community distro
Ubuntu
Community-rebuilt distros
CentOS, Scientific Linux
Mcamcamca @ Flickr

3. Stability
Use old versions
Backport significant new functionality / bug fixes
Supportability
Don’t try to support everything
Pick one technology and support that one well
Eliminate all non-supported technologies

4. Community-rebuilt distro
...with a twist
SIG =
Special Interest Group

5. Released 10 July 2011
6 months after the release 10000’s of users still using CentOS 5
The reason? Xen Project
RHEL had purchased Qumranet
Made KVM the hypervisor of choice for RHEL6
Tons of users who still wanted to use Xen
CentOS community members approached the Xen Community
At FOSDEM 2012, we started to make a plan to fix this

6. Supplementary yum repo
Xen
Domain 0 kernel
libvirt

7. What if people want all the boring, slow-changing
stability of an enterprise kernel, except...
...for one application, where they want something newer?
...a different technology than the one chosen by the “commercial
upstream”?

8. Community-developed “patches” on the immutable core
Mechanism:
Additional yum repo that adds / overrides core packages
General approach: Make it up as we go along
Mcamcamca @ Flickr

9. SIGs Approved:
Cloud SIG (OpenStack, &co )
Cloud Instance SIG (Amazon instances, &c)
Virtualization (Xen, Docker, oVirt)
Storage (CentOS as a storage node)
Atomic
... it would seem so!

10. Maria Ly @ Flickr
Issues we have worked through
in the last 12 months
Some are not yet fully resolved

11. Moving from a small tight-knit group to larger disaggregated groups
Everyone’s trusted to
Want to trust everyone, but trust needs to be limited
Not unique to CentOS model
Complicated by the already-large community
Also See:
cbs.centos.org/koji/
wiki.centos.org/HowTos/CommunityBuildSystem
CERN CentOS Dojo presentation @ bit.do/centos-sig-cbs

12. Not even minor fixes can be added to the CentOS-Core
So even minor changes mean re-building the whole package
Example: virt-install uses blktap1 instead of blktap2
Re-building also means tracking Core changes
Nicholas A. Tonelli @ Flickr

13. Example:
Docker for C7 (in the Virt SIG) uses stock C7 kernel
Xen for C7 will need a domain-0 enabled kernel
Solutions:
Break down into virt7-xen and virt7-docker repos
Share the same SIG delivered kernel
Challenge: Avoiding repo multiplication
Mcamcamca @ Flickr

14. What if you want to install two different SIGs, but:
The two SIGs require different versions of the same package
(e.g., the kernel)
General approach:
We’ll figure it out when we get there.
Mcamcamca @ Flickr

15. CentOS core has the stability guarantees of the upstream enterprise OS
CentOS SIGs don’t have nearly as much testing behind them
But they still carry the CentOS name
Oversight by CentOS board member important

16. Maintainers having taken ownership for several technologies:
Xen, Docker, oVirt
wiki.centos.org/SpecialInterestGroup/Virtualization

17. Done:
Projects building in the community build system for CentOS 6
Updated to Xen 4.4.1 and libvirt 1.2.10
Already a user: “yum update”
wiki.centos.org/HowTos/Xen/Xen4QuickStart
To-do:
Build for CentOS 7
Update kernel to 3.14
(currently 3.10)

18. Docker 1.4.1 for CentOS 7 in CBS
Close to release (in testing, tag “virt7-testing”)
Working on Rocket

19. Added to Virt SIG 6 weeks ago
Goals:
Build qemu-kvm binary with live snapshot support
oVirt Live “spin”
oVirt Node “spin”
Interface with Storage SIG …
for GlusterFS support

20. See if there’s an existing SIG you can join
E-mail centos-devel with your proposal
Convince one of the CentOS Board members to sponsor you.
wiki.centos.org/SpecialInterestGroup
www.centos.org/about/governance/sigs

21. Slides on www.slideshare.net/xen_com_mgr/