cloud-initramfs-dyn-netconf should work without /etc/network/interfaces symlink

[Scott Moser]

See [1] for doc on cloud-initramfs-dyn-netconf.

cloud-initramfs-dyn-netconf takes klibc ipconfig output and writes /etc/network/interfaces (ENI) style file in /run/network/dynamic-interfaces.
The goal is to have the user's provided 'ip=' kernel parameters be "sticky" and not have the network interface get bounced by normal post-initramfs networking bringup. Essentially kernel command line should override /etc/network/interfaces in a similar way to command line flags overriding environment or system configuration.

As it is right now, we have to have ln -sf /etc/network/interfaces /run/network/dynamic-interfaces in order for this to work.
That means:
 a.) if you've not done this, dyn-netconf isn't much use
 b.) if you *have* done this, but not provided ip= then you'll get you'll get no network configuration.

In xenial, the one necessary change from a cloud image to maas image is this symlink, so that the image can work well with networking information being provided on the kernel command line via network boot.

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[1] http://bazaar.launchpad.net/~cloud-initramfs-tools/cloud-initramfs-tools/trunk/view/head:/dyn-netconf/doc/README.txt

[Scott Moser (smoser)]

The fix that went in to xenial for this (and present in current yakkety and trunk cloud-init) is for cloud-init to read its networking configuration effectively from the kernel command line.

If cloud-init sees network-config= or ip= on the kernel command line, then it will parse the /run/net-*.conf files that are written by the ipconfig in the initramfs and use them as a source of networking information. The kernel's command line overrides a datasource or builtin configuration, so the end result is that the 'ip=' declares the system's network configuration.

[Scott Moser (smoser)]

cloud-init in xenial can now handle this so I've just explicitly marked this fix-released there.