For me the strong point about RHEL/CentOS is the long term support (as in really long term support, 10y) and continuous back-porting of important features making it a lot less obsolete than it may appear. This is extremely important and many fail to actually realise it.
In comparison, Ubuntu 10.04 released in the same year as RHEL 6 (2010) has aged much more severely.
e.g. EL 6.4 brings Openvswitch and improved namespace support in kernel (particularly interesting for openstack fans) among many other things (see tech notes[1]).
While it may not be as flexible as Debian or have the huge community Ubuntu boasts nowadays, RHEL brings a lot of reassuring predictability and stability to the table. I have come to appreciate this a lot in my years working as a sysadmin.
Also a note on people's praising the "smooth" upgrades between Debian major releases and the less than smooth upgrades between RHEL/Centos major releases:
1 - please do keep in mind that RHEL releases are very long lived in the meanwhile technology changes a lot; transitioning from kernel 2.4 to 2.6 has been very tricky for example, or from SysVinit to Upstart (and to Systemd in RHEL 7). It's dificult to foolproof such migrations so the task is left to the sysadmins - plus you always have a LOT of time to plan and do this. And ...
2 - Also, while the upgrade process itself has been successful and I get a booting OS with Debian, after a dist-upgrade, there are APIs, ABIs, major versions of software etc that have changed in the new OS and potentially breaking a lot of stuff in very ugly ways.
Having said that both platforms have their place and their strengths and I think they complement each other very well to the point that through them we now have a server market massively dominated by Linux. Thanks god. ;-)
Major upgrades are a non-issue on RHEL for the simple fact that when you are thinking about upgrading, your hardware is already obsolete (expensive to support) and you just migrate to a new machine instead of upgrading the existing one.
Having a RHEL install supported for 10 years and then upgrading in-place just doesn't make sense in 90% of the shops using RHEL (that choose it exactly because of those 10 years of support).
In comparison, Ubuntu 10.04 released in the same year as RHEL 6 (2010) has aged much more severely.
e.g. EL 6.4 brings Openvswitch and improved namespace support in kernel (particularly interesting for openstack fans) among many other things (see tech notes[1]).
While it may not be as flexible as Debian or have the huge community Ubuntu boasts nowadays, RHEL brings a lot of reassuring predictability and stability to the table. I have come to appreciate this a lot in my years working as a sysadmin.
Also a note on people's praising the "smooth" upgrades between Debian major releases and the less than smooth upgrades between RHEL/Centos major releases:
1 - please do keep in mind that RHEL releases are very long lived in the meanwhile technology changes a lot; transitioning from kernel 2.4 to 2.6 has been very tricky for example, or from SysVinit to Upstart (and to Systemd in RHEL 7). It's dificult to foolproof such migrations so the task is left to the sysadmins - plus you always have a LOT of time to plan and do this. And ...
2 - Also, while the upgrade process itself has been successful and I get a booting OS with Debian, after a dist-upgrade, there are APIs, ABIs, major versions of software etc that have changed in the new OS and potentially breaking a lot of stuff in very ugly ways.
Having said that both platforms have their place and their strengths and I think they complement each other very well to the point that through them we now have a server market massively dominated by Linux. Thanks god. ;-)
[1] - https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enter...