net: add renderers for automatically selecting the renderer.

Previously, the distro had hard coded which network renderer it would
use. This adds support for just picking the right renderer based
on what is available.

Now, that can be set via a priority in system_info, but should
generally work. That config looks like:
 system_info:
   network:
     renderers: ["eni", "sysconfig"]

When no renderers are found, a specific RendererNotFoundError is raised.
stages.py is modified to catch that and log it at error level. This
path should not really be exercised, but could occur if for example an
Ubuntu system did not have ifupdown, or a rhel system did not have
sysconfig. In such a system previously we would have quietly rendered
ENI configuration but that would have been ignored. This is one step
better in that we at least log the error.

3 files changed, 24 insertions, 19 deletions

diff --git a/cloudinit/distros/__init__.py b/cloudinit/distros/__init__.py
index f3d395b9..803ac74e 100755
--- a/cloudinit/distros/__init__.py
+++ b/cloudinit/distros/__init__.py
@@ -22,6 +22,7 @@ from cloudinit import log as logging
 from cloudinit import net
 from cloudinit.net import eni
 from cloudinit.net import network_state
+from cloudinit.net import renderers
 from cloudinit import ssh_util
 from cloudinit import type_utils
 from cloudinit import util
@@ -50,6 +51,7 @@ class Distro(object):
     hostname_conf_fn = "/etc/hostname"
     tz_zone_dir = "/usr/share/zoneinfo"
     init_cmd = ['service']  # systemctl, service etc
+    renderer_configs = {}
 
     def __init__(self, name, cfg, paths):
         self._paths = paths
@@ -69,6 +71,17 @@ class Distro(object):
     def _write_network_config(self, settings):
         raise NotImplementedError()
 
+    def _supported_write_network_config(self, network_config):
+        priority = util.get_cfg_by_path(
+            self._cfg, ('network', 'renderers'), None)
+
+        name, render_cls = renderers.select(priority=priority)
+        LOG.debug("Selected renderer '%s' from priority list: %s",
+                  name, priority)
+        renderer = render_cls(config=self.renderer_configs.get(name))
+        renderer.render_network_config(network_config=network_config)
+        return []
+
     def _find_tz_file(self, tz):
         tz_file = os.path.join(self.tz_zone_dir, str(tz))
         if not os.path.isfile(tz_file):
diff --git a/cloudinit/distros/debian.py b/cloudinit/distros/debian.py
index 48ccec8c..1101f02d 100644
--- a/cloudinit/distros/debian.py
+++ b/cloudinit/distros/debian.py
@@ -13,8 +13,6 @@ import os
 from cloudinit import distros
 from cloudinit import helpers
 from cloudinit import log as logging
-from cloudinit.net import eni
-from cloudinit.net.network_state import parse_net_config_data
 from cloudinit import util
 
 from cloudinit.distros.parsers.hostname import HostnameConf
@@ -38,11 +36,18 @@ ENI_HEADER = """# This file is generated from information provided by
 # network: {config: disabled}
 """
 
+NETWORK_CONF_FN = "/etc/network/interfaces.d/50-cloud-init.cfg"
+
 
 class Distro(distros.Distro):
     hostname_conf_fn = "/etc/hostname"
     locale_conf_fn = "/etc/default/locale"
-    network_conf_fn = "/etc/network/interfaces.d/50-cloud-init.cfg"
+    renderer_configs = {
+        'eni': {
+            'eni_path': NETWORK_CONF_FN,
+            'eni_header': ENI_HEADER,
+        }
+    }
 
     def __init__(self, name, cfg, paths):
         distros.Distro.__init__(self, name, cfg, paths)
@@ -51,12 +56,6 @@ class Distro(distros.Distro):
         # should only happen say once per instance...)
         self._runner = helpers.Runners(paths)
         self.osfamily = 'debian'
-        self._net_renderer = eni.Renderer({
-            'eni_path': self.network_conf_fn,
-            'eni_header': ENI_HEADER,
-            'links_path_prefix': None,
-            'netrules_path': None,
-        })
 
     def apply_locale(self, locale, out_fn=None):
         if not out_fn:
@@ -76,14 +75,12 @@ class Distro(distros.Distro):
         self.package_command('install', pkgs=pkglist)
 
     def _write_network(self, settings):
-        util.write_file(self.network_conf_fn, settings)
+        util.write_file(NETWORK_CONF_FN, settings)
         return ['all']
 
     def _write_network_config(self, netconfig):
-        ns = parse_net_config_data(netconfig)
-        self._net_renderer.render_network_state("/", ns)
         _maybe_remove_legacy_eth0()
-        return []
+        return self._supported_write_network_config(netconfig)
 
     def _bring_up_interfaces(self, device_names):
         use_all = False
diff --git a/cloudinit/distros/rhel.py b/cloudinit/distros/rhel.py
index 7498c63a..372c7d0f 100644
--- a/cloudinit/distros/rhel.py
+++ b/cloudinit/distros/rhel.py
@@ -11,8 +11,6 @@
 from cloudinit import distros
 from cloudinit import helpers
 from cloudinit import log as logging
-from cloudinit.net.network_state import parse_net_config_data
-from cloudinit.net import sysconfig
 from cloudinit import util
 
 from cloudinit.distros import net_util
@@ -49,16 +47,13 @@ class Distro(distros.Distro):
         # should only happen say once per instance...)
         self._runner = helpers.Runners(paths)
         self.osfamily = 'redhat'
-        self._net_renderer = sysconfig.Renderer()
         cfg['ssh_svcname'] = 'sshd'
 
     def install_packages(self, pkglist):
         self.package_command('install', pkgs=pkglist)
 
     def _write_network_config(self, netconfig):
-        ns = parse_net_config_data(netconfig)
-        self._net_renderer.render_network_state("/", ns)
-        return []
+        return self._supported_write_network_config(netconfig)
 
     def _write_network(self, settings):
         # TODO(harlowja) fix this... since this is the ubuntu format