[libvirt-users] Why does libvirt use XML firewall rules?

[Daniel P. Berrange]

On Mon, Dec 12, 2011 at 02:19:38PM +0100, Hansa wrote:
> Hi there,
> 
>  
> 
> When creating a VM with a persistent virtual network, libvirt creates an XML
> file with firewall definitions and stores it in
> /etc/libvirt/<hypervisor>/networks/. The XML file is (to my knowledge)
> incompatible with iptables-restore. Therefore you can’t manage your firewall
> with other iptables (GUI) tools unless libvirt lets you a) import extra
> rules, b) has an option to export the XML rules into iptables-save format or
> c) something else. If a) , b) or c) is possible then this discussion is of
> course useless and I would be pleased to know how it’s done :)
> 
> If not, then let’s get the discussion started.
> 
> IMHO, saving rules into XML instead of using iptables-save is absurd since
> you’ll have to code stuff which is already coded. Also you’ll make it
> incompatible with the tools which are readily available. Why go for this
> approach and what do we get from it?

The core goal of libvirt is to provide data formats which are independent
of any particular implementation, so that they are portable across all
hypervisors / OS / releases. If we uses iptables CLI as a data format,
this would not be portable to Windows, BSD, OS-X. It would not even be
portable to future Linux which may use the firewalld daemon over DBus
instead of direct iptables rule manipulation.

Furthermore the Fedora iptables-save/restore impl as it stands is really
an unfixably broken design since it is designed around the idea of a
statically configured firewall. Back in the real world, firewalls need
to really dynamically change as services change on the host. This is
why Fedora is aiming to kill it off by creating firewalld

Regards,
Daniel
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