Subject: Re: [systemd-devel] [PATCH] netns: unix: only allow to find out unix socket in same net namespace

From: Gao feng <[email-masked]>
Date: Mon, 26 Aug 2013 09:06:43 +0800

On 08/26/2013 02:16 AM, James Bottomley wrote:
> On Sun, 2013-08-25 at 19:37 +0200, Kay Sievers wrote:
>> On Sun, Aug 25, 2013 at 7:16 PM, James Bottomley
>> <[email-masked]> wrote:
>>> On Wed, 2013-08-21 at 11:51 +0200, Kay Sievers wrote:
>>>> On Wed, Aug 21, 2013 at 9:22 AM, Gao feng <[email-masked]> wrote:
>>>>> On 08/21/2013 03:06 PM, Eric W. Biederman wrote:
>>>>
>>>>>> I suspect libvirt should simply not share /run or any other normally
>>>>>> writable directory with the host.  Sharing /run /var/run or even /tmp
>>>>>> seems extremely dubious if you want some kind of containment, and
>>>>>> without strange things spilling through.
>>>>
>>>> Right, /run or /var cannot be shared. It's not only about sockets,
>>>> many other things will also go really wrong that way.
>>>
>>> This is very narrow thinking about what a container might be and will
>>> cause trouble as people start to create novel uses for containers in the
>>> cloud if you try to impose this on our current infrastructure.
>>>
>>> One of the cgroup only container uses we see at Parallels (so no
>>> separate filesystem and no net namespaces) is pure apache load balancer
>>> type shared hosting.  In this scenario, base apache is effectively
>>> brought up in the host environment, but then spawned instances are
>>> resource limited using cgroups according to what the customer has paid.
>>> Obviously all apache instances are sharing /var and /run from the host
>>> (mostly for logging and pid storage and static pages).  The reason some
>>> hosters do this is that it allows much higher density simple web serving
>>> (either static pages from quota limited chroots or dynamic pages limited
>>> by database space constraints) because each "instance" shares so much
>>> from the host.  The service is obviously much more basic than giving
>>> each customer a container running apache, but it's much easier for the
>>> hoster to administer and it serves the customer just as well for a large
>>> cross section of use cases and for those it doesn't serve, the hoster
>>> usually has separate container hosting (for a higher price, of course).
>>
>> The "container" as we talk about has it's own init, and no, it cannot
>> share /var or /run.
> 
> This is what we would call an IaaS container: bringing up init and
> effectively a new OS inside a container is the closest containers come
> to being like hypervisors.  It's the most common use case of Parallels
> containers in the field, so I'm certainly not telling you it's a bad
> idea.
> 
>> The stuff you talk about has nothing to do with that, it's not
>> different from all services or a multi-instantiated service on the
>> host sharing the same /run and /var.
> 
> I gave you one example: a really simplistic one.  A more sophisticated
> example is a PaaS or SaaS container where you bring the OS up in the
> host but spawn a particular application into its own container (this is
> essentially similar to what Docker does).  Often in this case, you do
> add separate mount and network namespaces to make the application
> isolated and migrateable with its own IP address.  The reason you share
> init and most of the OS from the host is for elasticity and density,
> which are fast becoming a holy grail type quest of cloud orchestration
> systems: if you don't have to bring up the OS from init and you can just
> start the application from a C/R image (orders of magnitude smaller than
> a full system image) and slap on the necessary namespaces as you clone
> it, you have something that comes online in miliseconds which is a feat
> no hypervisor based virtualisation can match.
> 
> I'm not saying don't pursue the IaaS case, it's definitely useful ...
> I'm just saying it would be a serious mistake to think that's the only
> use case for containers and we certainly shouldn't adjust Linux to serve
> only that use case.
>

The feature you said above VS contianer-reboot-host bug, I prefer to fix
the bug. and this feature can be achieved even container unshares /run directory
with host by default, for libvirt, user can set the container configuration to
make the container shares the /run directory with host.

I would like to say, the reboot from container bug is more urgent and need
to be fixed.