Re: [RFC] Per-user namespace process accounting

[Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>]

Quoting Marian Marinov (mm-108MBtLGafw@public.gmane.org):
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> On 05/29/2014 01:06 PM, Eric W. Biederman wrote:
> > Marian Marinov <mm-108MBtLGafw@public.gmane.org> writes:
> > 
> >> Hello,
> >> 
> >> I have the following proposition.
> >> 
> >> Number of currently running processes is accounted at the root user namespace. The problem I'm facing is that
> >> multiple containers in different user namespaces share the process counters.
> > 
> > That is deliberate.
> 
> And I understand that very well ;)
> 
> > 
> >> So if containerX runs 100 with UID 99, containerY should have NPROC limit of above 100 in order to execute any 
> >> processes with ist own UID 99.
> >> 
> >> I know that some of you will tell me that I should not provision all of my containers with the same UID/GID maps,
> >> but this brings another problem.
> >> 
> >> We are provisioning the containers from a template. The template has a lot of files 500k and more. And chowning
> >> these causes a lot of I/O and also slows down provisioning considerably.
> >> 
> >> The other problem is that when we migrate one container from one host machine to another the IDs may be already
> >> in use on the new machine and we need to chown all the files again.
> > 
> > You should have the same uid allocations for all machines in your fleet as much as possible.   That has been true
> > ever since NFS was invented and is not new here.  You can avoid the cost of chowning if you untar your files inside
> > of your user namespace.  You can have different maps per machine if you are crazy enough to do that.  You can even
> > have shared uids that you use to share files between containers as long as none of those files is setuid.  And map
> > those shared files to some kind of nobody user in your user namespace.
> 
> We are not using NFS. We are using a shared block storage that offers us snapshots. So provisioning new containers is
> extremely cheep and fast. Comparing that with untar is comparing a race car with Smart. Yes it can be done and no, I
> do not believe we should go backwards.
> 
> We do not share filesystems between containers, we offer them block devices.

Yes, this is a real nuisance for openstack style deployments.

One nice solution to this imo would be a very thin stackable filesystem
which does uid shifting, or, better yet, a non-stackable way of shifting
uids at mount.