net/network_manager: do not set "may-fail" to False for both ipv4 and…

… ipv6 dhcp

If "may-fail" is set to False in the Network Manager keyfile for both ipv4
and ipv6 for dhcp configuration, it essentially means both ipv4 and ipv6 network
initialization using dhcp must succeed for the overall network configuration to
succeed. This means, for environments where only ipv4 or ipv6 is available but
not both and we need to configure both ipv4 and ipv6 dhcp, the overall
network configuration will fail. This is not what we want. When both ipv4
and ipv6 dhcp are configured, it is enough for the overall configuration to
succeed if any one succeeds.
Therefore, set "may-fail" to True for both ipv4 and ipv6 if and only if both
ipv4 and ipv6 are configured as dhcp in the Network Manager keyfile and
"may-fail" is set to False for both. If both ipv4 and ipv6 are configured
in the keyfile and if for any of them "may-fail" is already set to True,then
do nothing.
All other cases remain same as before.

Please see discussions in PR canonical#4474.

Co-authored-by: James Falcon <james.falcon@canonical.com>
Signed-off-by: Ani Sinha <anisinha@redhat.com>

cloudinit/net/network_manager.py

@@ -71,6 +71,60 @@ def _set_default(self, section, option, value):
         if not self.config.has_option(section, option):
             self.config[section][option] = value
 
+    def _config_option_is_set(self, section, option):
+        """
+        Checks if a config option is set. Returns True if it is,
+        else returns False.
+        """
+        return self.config.has_section(section) and self.config.has_option(
+            section, option
+        )
+
+    def _get_config_option(self, section, option):
+        """
+        Returns the value of a config option if its set,
+        else returns None.
+        """
+        if self._config_option_is_set(section, option):
+            return self.config[section][option]
+        else:
+            return None
+
+    def _change_set_config_option(self, section, option, value):
+        """
+        Overrides the value of a config option if its already set.
+        Else, if the config option is not set, it does nothing.
+        """
+        if self._config_option_is_set(section, option):
+            self.config[section][option] = value
+
+    def _set_mayfail_true_if_both_false_dhcp(self):
+        """
+        If for both ipv4 and ipv6, 'may-fail' is set to be False,
+        set it to True for both of them.
+        """
+        for family in ["ipv4", "ipv6"]:
+            if (
+                not self._config_option_is_set(family, "may-fail")
+                or self._get_config_option(family, "may-fail") != "false"
+            ):
+                # if either ipv4 or ipv6 sections are not set/configured,
+                # or if for either ipv4 or ipv6, 'may-fail' is not 'false', do
+                # not do anything.
+                return
+            if self._get_config_option(family, "method") not in [
+                "dhcp",
+                "auto",
+            ]:
+                # if both v4 and v6 are not dhcp, do not do anything.
+                return
+
+        # If we landed here, it means both ipv4 and ipv6 are configured
+        # with dhcp/auto and both have 'may-fail' set to 'false'. So set
+        # both to 'true'.
+        for family in ["ipv4", "ipv6"]:
+            self._change_set_config_option(family, "may-fail", "true")
+
     def _set_ip_method(self, family, subnet_type):
         """
         Ensures there's appropriate [ipv4]/[ipv6] for given family
@@ -271,6 +325,14 @@ def render_interface(self, iface, renderer):
             if family == "ipv4" and "mtu" in subnet:
                 ipv4_mtu = subnet["mtu"]
 
+        # we do not want to set may-fail to false for both ipv4 and ipv6 dhcp
+        # at the at the same time. This will make the network configuration
+        # work only when both ipv4 and ipv6 dhcp succeeds. This may not be
+        # what we want. If we have configured both ipv4 and ipv6 dhcp, any one
+        # succeeding should be enough. Therefore, if "may-fail" is set to
+        # False for both ipv4 and ipv6 dhcp, set them both to True.
+        self._set_mayfail_true_if_both_false_dhcp()
+
         if ipv4_mtu is None:
             ipv4_mtu = device_mtu
         if not ipv4_mtu == device_mtu:

tests/unittests/test_net.py

@@ -1425,11 +1425,11 @@
 
                 [ipv4]
                 method=auto
-                may-fail=false
+                may-fail=true
 
                 [ipv6]
                 method=auto
-                may-fail=false
+                may-fail=true
 
                 """
             ),
@@ -1598,11 +1598,11 @@
 
                 [ipv6]
                 method=auto
-                may-fail=false
+                may-fail=true
 
                 [ipv4]
                 method=auto
-                may-fail=false
+                may-fail=true
 
                 """
             ),