Good for you. When you say, "OVH server", I'm guessing you mean a dedicated.
Here's what I've noticed. The older servers will be used for VPS classic. Discourse is out of the picture there. You need at least later versions of 3.13x to run docker, as aufs is not provided with the older kernels.
With the VPS cloud, it seems the standard kernel which they will give out is an earlier 3.10 kernel, which will not work. Some people have reported success by recompiling the kernel, but I'm seeing no confirmation that their working version properly addresses a sub-domain specifically, and therefore would work for multiple instances.
I have a kimsufi ks-3, and had no issues getting the later kernel flipped without breaking bind9. It seems the issue is with the "cloud" environment. With the VPS cloud, I did try the ubuntu repository for docker.io, but that didn't work out. You can't load docker without aufs. Aufs is not available on some of the earlier kernels.
My guess is that the majority, if not all, of the dedicated servers either have the later kernel already installed with their selected distributions, else can easily be upgraded. The problem seems isolated to the VPS from OVH.