Add a enable_internal_subnet config item which doesn't create internal

subnets and NATs.

Signed-off-by: Arjun Naik <arjun.rn@gmail.com>

sevenseconds/config/vpc.py

@@ -83,16 +83,20 @@ def configure_vpc(account: AccountData, region, base_ami_id):
                 if not account.dry_run:
                     subnet.delete()
 
+    enable_internal = account.config.get("enable_internal_subnets", True)
     # Configure subnets
     if vpc_config and 'subnets' in vpc_config:
         subnets = custom_subnets(vpc_net, vpc_config['subnets'], availability_zones)
     else:
-        subnets = default_subnets(vpc_net, availability_zones)
+        subnets = default_subnets(vpc_net, availability_zones, enable_internal)
 
     for subnet in subnets:
         configure_subnet(vpc, subnet, account.dry_run, ec2c.get_waiter('subnet_available'))
 
-    nat_instances = create_nat_instances(account, vpc, region)
+    if enable_internal:
+        nat_instances = create_nat_instances(account, vpc, region)
+    else:
+        nat_instances = {}
     create_routing_tables(vpc, nat_instances,
                           account.options.get('re_add_defaultroute', False),
                           account.config.get('enable_dedicated_dmz_route', False))
@@ -110,8 +114,11 @@ def custom_subnets(vpc_net, subnet_config, availability_zones):
             yield Subnet(az, subnet['type'], cidr, subnet.get('tags', {}))
 
 
-def default_subnets(vpc_net, availability_zones):
-    for subnet_type in 'dmz', 'internal':
+def default_subnets(vpc_net, availability_zones, enable_internal: bool):
+    subnet_types = ['dmz']
+    if enable_internal:
+        subnet_types.append('internal')
+    for subnet_type in subnet_types:
         for i, az in enumerate(sorted(availability_zones)):
             tags = {}
             if subnet_type == 'dmz':