Sadly, we're moving away from Red Hat Enterprise Linux
There are two versions of this story. In one version I'd start by noting that RHEL never really caught on here because it wasn't enough better than Ubuntu LTS to be mostly worth the hassle, mention our iSCSI backends as the exception, and then explain that as part of turning over that entire infrastructure we decided that we might as well run Ubuntu LTS on the backends instead of RHEL. This is somewhat more sensible than it might look; our backends are essentially appliances that we almost never update, we don't allow access to them, and they run custom kernels and software anyways so the actual distribution is doing almost nothing.
This version of the story is true but it is not the real story, or at least not the full story. To start the full story I have to say that when I say 'RHEL' here I really mean RHEL, not CentOS, because for a long time the university has had an (inexpensive) site-wide RHEL license. With that background, there are three reasons we're moving away from RHEL.
First, this year we had major, multi-month problems getting RHEL to renew our site license and for a while it looked like we would not be able to afford to renew it at all. This was quite disruptive, a lot of people are unhappy with Red Hat (especially the people who actually pay for the license), and the future of our site license is now both uncertain and precarious. One way or another it's probably not lasting more than a year or two more. This means moving away from genuine RHEL to, say, CentOS.
Second, I'm not enthused about RHEL 6 and the timing for using it is not great because it's now been three years since it was released. As a result I have no real enthusiasm for using RHEL 6 on anything right now.
What we'd like to use is RHEL 7, but there are two problems together that make up the third reason. Not only is RHEL 7 not out yet, but our forced switch to CentOS means that we need to wait not just for the RHEL 7 release but for CentOS to (re)build a CentOS 7. This is a risky wait because it's a lot of work; it's almost certainly going to take CentOS a not insignificant amount of time to do. Between both delays, it could be a year before CentOS 7 is available and we need new iSCSI backends long before then.
(When I looked into RHEL 6 and said 'let's wait until RHEL 7', as covered in an earlier entry, it was pretty early in 2013 and the first and the third thing hadn't happened yet. So I expected RHEL 7 before the end of 2013 and did not know we would hit major license issues.)
I'm sad about this. I genuinely like RHEL and generally prefer it to Ubuntu LTS. But through this combination of factors it is effectively dead here.
Sidebar: the risks of CentOS
I've argued before that the risks of using CentOS instead of RHEL are relatively small once CentOS has put out an initial major release (eg CentOS 7). However, 'small' is not 'zero' and yes, this factor is in the back of my mind when I consider using CentOS here.
(The recent Red Hat acquisition of CentOS does not reduce this. If anything it increases it, since Red Hat has been very bland about why it's doing this and whether (and how) CentOS is going to change as a result of it. As a result plenty of people are speculating about potential results and changes, some of which are things we would very much not want.)