Comment 13 for bug 1843634

The patch that is in the 19.1 package that is currently distributed in openSUSE and SLE to avoid writing an "empty" config file is as follows:

--- cloudinit/net/sysconfig.py.orig
+++ cloudinit/net/sysconfig.py
@@ -545,6 +545,8 @@ class Renderer(renderer.Renderer):
             content.add_nameserver(nameserver)
         for searchdomain in network_state.dns_searchdomains:
             content.add_search_domain(searchdomain)
+ if not str(content):
+ return str(content)
         header = _make_header(';')
         content_str = str(content)
         if not content_str.startswith(header):
@@ -658,7 +660,8 @@ class Renderer(renderer.Renderer):
             dns_path = util.target_path(target, self.dns_path)
             resolv_content = self._render_dns(network_state,
                                               existing_dns_path=dns_path)
- util.write_file(dns_path, resolv_content, file_mode)
+ if resolv_content:
+ util.write_file(dns_path, resolv_content, file_mode)
         if self.networkmanager_conf_path:
             nm_conf_path = util.target_path(target,
                                             self.networkmanager_conf_path)

This is basically the same as in in "master". In "master" instead of returning an empty string, content is initialized to resolv_conf.ResolvConf(""), None is returned. This means in master "_render_dns()" has different return types, which is a style choice and that's a different discussion.

From a code perspective the package delivers the equivalent to what is in master. Next step for me is to do some testing in Azure.