Ensure custom mode VPC networks can be created

PiperOrigin-RevId: 697135144

perfkitbenchmarker/providers/gcp/flags.py

@@ -76,8 +76,15 @@
     'The name of an already created '
     'network to use instead of creating a new one.',
 )
-GCE_NETWORK_TYPE = flags.DEFINE_string(
-    'gce_network_type', None, 'The network type or mode (i.e. auto, custom)'
+GCE_NETWORK_TYPE = flags.DEFINE_enum(
+    'gce_network_type',
+    None,
+    [
+        'auto',
+        'custom',
+        'legacy',
+    ],
+    'The subnet mode of the network (i.e. auto, custom, legacy)',
 )
 GCE_SUBNET_NAMES = flags.DEFINE_list(
     'gce_subnet_name',

perfkitbenchmarker/providers/gcp/gce_network.py

@@ -918,13 +918,18 @@ def __init__(self, network_spec: GceNetworkSpec):
     self.subnet_resources = []
     mode = gcp_flags.GCE_NETWORK_TYPE.value
     self.subnet_resource = None
+
+    # Handle GCP network attachment on legacy networks.
     if not self.is_existing_network or mode == 'legacy':
       for name in self.subnet_names:
-        mode = 'auto'
+        if mode != 'custom':
+          mode = 'auto'
         self.network_resources.append(
             GceNetworkResource(name, mode, self.project, self.mtu)
         )
-    else:
+
+    # Create GCP network subnet for custom mode.
+    if mode == 'custom':
       subnet_region = util.GetRegionFromZone(network_spec.zone)
       for name in self.subnet_names:
         self.subnet_resources.append(

tests/providers/gcp/gcp_network_test.py

@@ -380,8 +380,12 @@ def testSpecifyNetworkName(self):
     )
     net = gce_network.GceNetwork.GetNetwork(vm)
     self.assertTrue(net.is_existing_network)
-    self.assertEqual('my-network', net.network_resource.name)
-    self.assertEqual('my-network', net.subnet_resource.name)
+    name = (
+        net.subnet_resource.name
+        if net.subnet_resource
+        else net.network_resource.name
+    )
+    self.assertEqual('my-network', name)
 
   @flagsaver.flagsaver(
       gce_network_name=['my-network'],
@@ -410,8 +414,14 @@ def testSubnetFlagPrecedence(self):
         subnet_names='default',
     )
     net = gce_network.GceNetwork.GetNetwork(vm)
+    name = (
+        net.subnet_resource.name
+        if net.subnet_resource
+        else net.network_resource.name
+    )
+
     self.assertTrue(net.is_existing_network)
-    self.assertEqual('default', net.subnet_resource.name)
+    self.assertEqual('default', name)
 
   ########
   # FireWall Names