[Users] Docker inside an OpenVZ container

[Pavel Snajdr]

On 03/23/2015 11:01 PM, Kir Kolyshkin wrote:
> 
> 
> On 03/23/2015 03:12 AM, Benjamin Henrion wrote:
>> On Mon, Mar 23, 2015 at 10:55 AM, Narcis Garcia
>> <informatica at actiu.net> wrote:
>>> As I read from Ubuntu/Debian package (version 0.9.1):
>>>
>>> Docker complements kernel namespacing with a high-level API which
>>> operates at the process level. It runs unix processes with strong
>>> guarantees of isolation and repeatability across servers.
>>>
>>> Docker is a great building block for automating distributed systems:
>>> large-scale web deployments, database clusters, continuous deployment
>>> systems, private PaaS, service-oriented architectures, etc.
>>>
>>> This package contains the daemon and client. *Using docker.io on
>>> non-amd64 hosts is not supported at this time*. Please be careful when
>>> using it on anything besides amd64.
>>>
>>> Also, note that *kernel version 3.8 or above is required* for proper
>>> operation of the daemon process, and that any lower versions may have
>>> subtle and/or glaring issues.
>> Redhat backported a lot of LXC features to 2.6.32, so that's one of
>> the reasons you can run docker/lxc on top of the openvz kernel.
> 
> In addition to that, we did a significant amount of kernel work
> to allow running Docker inside our containers.
> 
> In general, OpenVZ kernel version (which is 2.6.32) has very little
> to do with vanilla 2.6.32, so this number doesn't really mean anything
> except that Red Hat kernel team branched their kernel off this
> version when they started working on RHEL6.
> 
> Currently this is 2.6.32 plus tons of patches from Red Hat plus
> a pretty big patchset from OpenVZ. In particular, we make sure all the
> recent distros work inside containers, so sometimes we have to backport
> some new syscall or other feature from recent kernels.
> 
> From time to time I see people saying OpenVZ kernel is very old and
> obsoleted. It happens because the judge by the label, and the label starts
> with 2.6.32. Indeed, 2.6.32 is a very old kernel, but as I explained above
> our kernel has very little to do with 2.6.32.

Hi Kir,

I've been telling those people just about the same thing, but recently I
don't think I can agree. I've become more involved in ZFS on Linux
development and we run on RHEL6 OpenVZ kernel. The core of RHEL6 is
getting old and there are lots and lots of improvement, that have gone
upstream, which improve mainly performance and multi-core scalability.
For instance and probably the most importantly for me now, I would like
to have VFS scalability patches, that have gone into upstream, in OpenVZ
RHEL6 kernel as well, as I'd like to see doing more granular eviction on
dentries. (http://lwn.net/Articles/636133/)

But this seems rather impossible, due to git/separated-out-patches not
being available for RHEL6 kernel and OpenVZ project following the suit.
I would have to invest a lot of time every time a rebase onto a newer
RHEL6 kernel release is made.

I would like to help out with OpenVZ development from time to time,
especially with things related to storage, but the project doesn't seem
all that open, you guys only publish your final results, but nothing
from the process of getting to them.

I don't mean to criticize or I don't mean it in any other bad way,
here's me just sighing at how things are. Do you see any room for change
in this regard? Or should we just leverage Parallels paid support for
OpenVZ to have you guys pull in the patches by yourselves?

I love open-source and doing things openly, I know that you guys don't
have a whole lot of breathing room thanks to Red Hat here, but is there
any possibility of opening the project up more?

Finally, I would like to thank all of you at the OpenVZ project, there
is no other usable container technology for Linux without you guys. I
highly respect that fact despite the relative closedness of the project.

/snajpa
(vpsFree.cz)

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