Support networkd RequiredForOnline option

Implement the "optional" ethernet interface property for the networkd
renderer. Marks an interface as not required for the network-online
target.

cloudinit/net/network_state.py

@@ -47,6 +47,7 @@
     "set-name",
     "wakeonlan",
     "accept-ra",
+    "optional",
 ]
 
 NET_CONFIG_TO_V2: Dict[str, Dict[str, Any]] = {
@@ -409,6 +410,9 @@ def handle_physical(self, command):
         wakeonlan = command.get("wakeonlan", None)
         if wakeonlan is not None:
             wakeonlan = util.is_true(wakeonlan)
+        optional = command.get("optional", None)
+        if optional is not None:
+            optional = util.is_true(optional)
         iface.update(
             {
                 "config_id": command.get("config_id"),
@@ -423,6 +427,7 @@ def handle_physical(self, command):
                 "subnets": subnets,
                 "accept-ra": accept_ra,
                 "wakeonlan": wakeonlan,
+                "optional": optional,
             }
         )
         iface_key = command.get("config_id", command.get("name"))
@@ -747,7 +752,7 @@ def handle_ethernets(self, command):
             driver = match.get("driver", None)
             if driver:
                 phy_cmd["params"] = {"driver": driver}
-            for key in ["mtu", "match", "wakeonlan", "accept-ra"]:
+            for key in ["mtu", "match", "wakeonlan", "accept-ra", "optional"]:
                 if key in cfg:
                     phy_cmd[key] = cfg[key]
 

cloudinit/net/networkd.py

@@ -122,6 +122,9 @@ def generate_link_section(self, iface, cfg: CfgParser):
         if "mtu" in iface and iface["mtu"]:
             cfg.update_section(sec, "MTUBytes", iface["mtu"])
 
+        if "optional" in iface and iface["optional"]:
+            cfg.update_section(sec, "RequiredForOnline", "no")
+
     def parse_routes(self, rid, conf, cfg: CfgParser):
         """
         Parse a route and use rid as a key in order to isolate the route from

doc/rtd/reference/network-config-format-v2.rst

@@ -264,6 +264,14 @@ The MTU key represents a device's Maximum Transmission Unit, the largest size
 packet or frame, specified in octets (eight-bit bytes), that can be sent in a
 packet- or frame-based network. Specifying ``mtu`` is optional.
 
+``optional: <(bool)>``
+------------------------
+
+Mark a device as not required for booting. By default networkd will wait for
+all configured interfaces to be configured before continuing to boot. This
+option causes networkd to not wait for the interface. This is only supported
+by networkd. The default is false.
+
 ``nameservers: <(mapping)>``
 ----------------------------
 

tests/unittests/net/test_networkd.py

@@ -10,6 +10,35 @@
 from cloudinit import safeyaml
 from cloudinit.net import network_state, networkd
 
+V2_CONFIG_OPTIONAL = """\
+network:
+  version: 2
+  ethernets:
+    eth0:
+      optional: true
+    eth1:
+      optional: false
+"""
+
+V2_CONFIG_OPTIONAL_RENDERED_ETH0 = """[Link]
+RequiredForOnline=no
+
+[Match]
+Name=eth0
+
+[Network]
+DHCP=no
+
+"""
+
+V2_CONFIG_OPTIONAL_RENDERED_ETH1 = """[Match]
+Name=eth1
+
+[Network]
+DHCP=no
+
+"""
+
 V2_CONFIG_SET_NAME = """\
 network:
   version: 2
@@ -452,6 +481,17 @@ def _parse_network_state_from_config(self, config):
             config = yaml.safe_load(config)
             return network_state.parse_net_config_data(config["network"])
 
+    def test_networkd_render_with_optional(self):
+        with mock.patch("cloudinit.net.get_interfaces_by_mac"):
+            ns = self._parse_network_state_from_config(V2_CONFIG_OPTIONAL)
+            renderer = networkd.Renderer()
+            rendered_content = renderer._render_content(ns)
+
+        assert "eth0" in rendered_content
+        assert rendered_content["eth0"] == V2_CONFIG_OPTIONAL_RENDERED_ETH0
+        assert "eth1" in rendered_content
+        assert rendered_content["eth1"] == V2_CONFIG_OPTIONAL_RENDERED_ETH1
+
     def test_networkd_render_with_set_name(self):
         with mock.patch("cloudinit.net.get_interfaces_by_mac"):
             ns = self._parse_network_state_from_config(V2_CONFIG_SET_NAME)