Yes, performance is probably one issue.
My concerns was for layer 2 / layer 3 virtualization. I agree a layer 2
isolation/virtualization is the best for the "system container".
But there is another family of container called "application container",
it is not a system which is run inside a container but only the
application. If you want to run a oracle database inside a container,
you can run it inside an application container without launching <init>
and all the services.
This family of containers are used too for HPC (high performance
computing) and for distributed checkpoint/restart. The cluster runs
hundred of jobs, spawning them on different hosts inside an application
container. Usually the jobs communicates with broadcast and multicast.
Application containers does not care of having different MAC address and
rely on a layer 3 approach.
Are application containers comfortable with a layer 2 virtualization ? I
don't think so, because several jobs running inside the same host
communicate via broadcast/multicast between them and between other jobs
running on different hosts. The IP consumption is a problem too: 1
container == 2 IP (one for the root namespace/ one for the container),
multiplicated with the number of jobs. Furthermore, lot of jobs == lot
of virtual devices.
However, after a discussion with Kirill at the OLS, it appears we can
merge the layer 2 and 3 approaches if the level of network
virtualization is tunable and we can choose layer 2 or layer 3 when
doing the "unshare". The determination of the namespace for the incoming
traffic can be done with an specific iptable module as a first step.
While looking at the network namespace patches, it appears that the
TCP/UDP part is **very** similar at what is needed for a layer 3 approach.
Any thoughts ?
My humble opinion is that your approach doesn't intersect with this one.
So we can freely go with both *if needed*.
And hear the comments from network guru guys and what and how to improve.
So I suggest you at least to send the patches, so we could discuss it.
Thanks,
Kirill
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