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

On 08/26/2013 11:19 AM, James Bottomley wrote: > On Mon, 2013-08-26 at 09:06 +0800, Gao feng wrote: >> 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 >>>> <jbottomley(a)parallels.com&gt; wrote: >>>>> On Wed, 2013-08-21 at 11:51 +0200, Kay Sievers wrote: >>>>>> On Wed, Aug 21, 2013 at 9:22 AM, Gao feng <gaofeng(a)cn.fujitsu.com&gt; 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. > > What 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. > > Are you talking about the old bug where trying to reboot an lxc > container from within it would reboot the entire system? Yes, we are discussing this problem in this whole thread. If so, OpenVZ > has never suffered from that problem and I thought it was fixed > upstream. I've not tested lxc tools, but the latest vzctl from the > openvz website will bring up a container on the vanilla 3.9 kernel > (provided you have USER_NS compiled in) can also be used to reboot the > container, so I see no reason it wouldn't work for lxc as well. > I'm using libvirt lxc not lxc-tools. Not all of users enable user namespace, I trust these container management tools can have right/proper setting which inhibit this reboot-problem occur. but I don't think this reboot-problem won't happen in any configuration.