Since I'm such a big container fan (been using them on Linux since 2005) and I recently blogged about Docker, LXC, and OpenVZ... how could I pass up posting this? Some Canonical guys gave a presentation at the recent OpenStack Summit on "LXD vs. KVM". What is LXD? It is basically a management service for LXC that supposedly adds a lot of the features LXC was missing... and is much easier to use. For a couple of years now Canonical has shown an interest in LXC and has supposedly be doing a lot of development work around them. I wonder what specifically? They almost seem like the only company who is interested in LXC.. or at least they are putting forth a publicly noticeable effort around them.
Why Should You Care?
If Canonical can actually deliver on their LXD roadmap it is possible that it will be a suitable substitute for OpenVZ. The main "problem" with OpenVZ is that it is not in the mainline kernel, whereas LXC is. In practice you have to purposefully make an OpenVZ host (currently recommended on RHEL6 or clone) but with LXC/LXD any contemporary Linux system should be able to do full-distro containers... aka containers everywhere for everyone.
How About a Roadmap
Where is LXD now? Well, so far it seems to be mostly a technology preview available in Ubuntu 15.04 with the target "usable and production ready" release slated for the next Ubuntu LTS release (16.04)... which if you weren't familiar with their numbering scheme is 2016 April.
That's about a year away, right... so what do they still have left to do? If you go to about 23:30 in the video you'll get to the "Roadmap" section. They have work to do on storage, networking, resource management and usage reporting, and live migration. A bit of that falls within the OpenStack context... integrating with various OpenStack components so containers will be more in parity with VMs for OpenStack users... but still, that's quite a bit of work.
The main thing I care about absolutely being there is isolation and resource management which are really the killer features of OpenVZ. So far as I can tell, LXD does not offer read-only base images and layering like Docker... so that would be an area for improvement I would suggest. BTW they are using CRIU for checkpointing and live migration... thanks Parallels/OpenVZ!
Certainly LXD won't really make it no matter how good it is until it is available in more Linux distributions than just Ubuntu. In a video interview a while back (which I don't have the link handy for at the moment) Mark Shuttleworth stated that he hopes and expects to see LXD in other distributions. One of the first distros I hope to see with LXD is Fedora and that's the reason I tagged this post appropriately.
Broadening the Echosystem
Historically I've been a bit of an anti-Canonical person but thinking more about it recently and taking the emotion out of it... I do wish Ubuntu success because we definitely need more FLOSS companies doing well financially in the market... and I think Red Hat (and OpenVZ) will have an incentive to do better. Competition is good, right? Anyway, enjoy the video. BTW, everything they tout as a benefit of LXD over KVM (density, speed of startup, scalability, etc) is also true of OpenVZ for almost a decade now.
For those with iFrame issues, here's the YouTube link:
LXD vs. KVM
Containers Should Contain
Let's face it, Docker (in its current form) sucks. Why? Well, ok... Docker doesn't totally suck... because it is for applications and not a full system... but if a container doesn't contain, it isn't a container. That's just how language works. If you have an airplane that doesn't fly, it isn't an airplane, right? Docker should really say it is an "Uncontainer" or "Uncontained containers"... or better yet, just use a different word. What word? I'm not sure. Do you have any suggestions? (Email me: email@example.com)
What is containment? For me it is really isolation and resource control. If a container doesn't do that well, call it something else. OpenVZ is a container. No, really. It contains. OpenVZ didn't start life using the word container. On day one they were calling them "Virtual Environments" (VEs). Then a year or two later they decided "Virtual Private Server" (VPS) was the preferred term. Some time after switching to VPS, VPS became quite ambiguous and used by hosting companies using hardware virtualization backends like Xen and VMware (KVM wasn't born yet or was still a baby). Then OpenVZ finally settled on the word "container".
If you want a fairly good history of the birth and growth of OpenVZ over the years, see Kir's recent presentation.
Hopefully LXD will live up to "container" but we'll have to wait and see.