Re: [RFC] Per-user namespace process accounting

[Pavel Emelyanov <xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On 05/29/2014 07:32 PM, Serge Hallyn wrote:
> 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.

I vote for non-stackable way too. Maybe on generic VFS level so that filesystems 
don't bother with it. From what I've seen, even simple stacking is quite a challenge.

Thanks,
Pavel