[ovs-discuss] Open-vswitch network configuration on Debian

[Ben Pfaff]

On Wed, Oct 26, 2011 at 01:37:08AM +0200, Hans van Kranenburg wrote:
> Perhaps it's best to consider the devices set up by ovs at boot time
> equal to the nics that are physically present in a server. Using
> this approach, I can just say "Yay, I have a switch built in to my
> server where I can plug in virtual machines!" (as if it were a
> physical hardware thing). Seems rather like a way of thinking you
> did want to achieve with this project anyway. ;]
> 
>  - Basic configuration of the switch takes place at the time I
> install my (e.g. Xen dom0) server. (yes, I can make changes later)
>  - OVS makes sure it will restore the configured setup when I reboot
> the machine.
>  - I can just use the 'normal' way of setting up links and
> configuring ip addresses and network routing using the ifupdown
> tools. Although it's not perfect, until now I've been able to
> perfectly abuse ifupdown and its hooks to do everything I wanted to
> do to set up and tear down interface configuration. (Note: this will
> *require* the 'networking' init script to be run *after* ovs sets up
> the devices!)

I mainly like the ideas behind this approach (I have considered
similar approaches before), but there are some difficulties.

A technical difficulty is that OVS installs many files under /usr, but
the Filesystem Hierarchy Standard that Linux distributions follow says
that /usr is supposed to be shareable, that is, it should be possible
for a number of machines to mount it from a network share.  This means
that files in /usr must not be needed to mount a network share.
Hence, OVS must not put anything in /usr.  Fine; we could move files
elsewhere.

This solution raises an organizational difficulty: /bin, /sbin, /lib,
etc. are supposed to be reserved for programs essential to booting
only.  I have not yet felt up to the task of arguing that
ovs-vswitchd, ovsdb-server, ovs-dpctl, and so on in fact fall into
this category.  Maybe it would not be a difficult hurdle to cross, or
maybe it would be, but I haven't done it yet.

> I'd also like, (I you agree) to ask the current maintainer of
> ifupdown in Debian (newsflash! someone is actually putting effort
> into ifupdown in Debian right now!) about his thoughts about these
> issues.

Please feel free to ask him.  You can CC me or ovs-discuss, if you
like.  Thank you for raising these issues.