do not render systemd.link files

When fixing bug 1579130, we made cloud-init rename devices itself,
rather than relying on the systemd.link files to do that.
That was necessary to
 - rename devices in a container
 - rename devices on first boot or in any situation when the 
   link files in the initramfs were stale.

However, cloud-init was still writing .link files like:
 /etc/systemd/network/50-cloud-init-ens2.link

That leads to just a confusing situation as cloud-init will trump
any renaming systemd does in all cases.

Also added here is a header into the rendered ENI file:
 /etc/network/interfaces.d/50-cloud-init.cfg

that describes how to disable cloud-init networking.

LP: #1594546

1 files changed, 3 insertions, 1 deletions

diff --git a/cloudinit/net/eni.py b/cloudinit/net/eni.py
index ccd16ba7..e5ed10fd 100644
--- a/cloudinit/net/eni.py
+++ b/cloudinit/net/eni.py
@@ -303,6 +303,7 @@ class Renderer(renderer.Renderer):
         if not config:
             config = {}
         self.eni_path = config.get('eni_path', 'etc/network/interfaces')
+        self.eni_header = config.get('eni_header', None)
         self.links_path_prefix = config.get(
             'links_path_prefix', 'etc/systemd/network/50-cloud-init-')
         self.netrules_path = config.get(
@@ -417,7 +418,8 @@ class Renderer(renderer.Renderer):
     def render_network_state(self, target, network_state):
         fpeni = os.path.join(target, self.eni_path)
         util.ensure_dir(os.path.dirname(fpeni))
-        util.write_file(fpeni, self._render_interfaces(network_state))
+        header = self.eni_header if self.eni_header else ""
+        util.write_file(fpeni, header + self._render_interfaces(network_state))
 
         if self.netrules_path:
             netrules = os.path.join(target, self.netrules_path)