On Wed, Jun 11, 2014 at 10:46:00AM -0500, David Chiluk wrote:
> On 06/11/2014 10:17 AM, Rafael Tinoco wrote:
> > This script simulates a failure on a cloud infrastructure, for ex. As soon
> > as
> > one virtualization host fails all its network namespaces have to be migrated
> > to other node. Creating thousands of netns in the shortest time possible
> > is the objective here. This regression was observed trying to migrate from
> > v3.5 to v3.8+.
> >
> > Script creates up to 3000/4000 thousands network namespaces and places
> > links on them. Every 250 mark (netns already created) we have a throughput
> > average (how many were created per second up from last mark to this one).
>
> Here's a little more background, and the "why it matters".
Thank you, this is quite helpful.
> In an openstack cloud, neutron *(openstack's networking framework) keeps
> all customers of the cloud separated via network namespaces. On each
> compute node this is not a big deal, since each compute node can only
> handle at most a few hundred VMs. However in order for neutron to route
> a customer's network traffic between disparate compute hosts, it uses
> the concept of a neutron gateway. In order for customer A's vm on host
> 1 to talk to customer A's vm on host 2, it must first go through a gre
> tunnel to the neutron gateway. The Neutron gateay then turns around and
> routes the network traffic over another gre tunnel to host 2. The
> neutron gateway is where the problem is.
>
> The neutron gateway must have a network namespace for every net
> namespace in the cloud. Granted this collection can be split up by
> increasing the number of neutron gateways *(scaling out), but some
> clouds have decided to run these gateways on very beefy machines. As
> you can see by the graph, there is a software limitation that prevents
> these machines from hosting any more than a few thousand namespaces.
> This makes the gateway's hardware severely under-utilized.
>
> Now think about what happens when a gateway goes down, the namespaces
> need to be migrated, or a new machine needs to be brought up to replace
> it. When we're talking about 3000 namespaces, the amount of time it
> takes simply to recreate the namespaces becomes very significant.
>
> The script is a stripped down example of what exactly is being done on
> the neutron gateway in order to create namespaces.
Are the namespaces torn down and recreated one at a time, or is there some
syscall, ioctl(), or whatever that allows bulk tear down and recreating?
Thanx, Paul
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