Create an externally routed OpenStack network

network.py

import os
from keystoneauth1 import identity, session
from neutronclient.v2_0 import client

def _neutron():
    creds = {
        "auth_url":          os.environ["OS_AUTH_URL"] + "/v3",
        "username":          os.environ["OS_USERNAME"],
        "password":          os.environ["OS_PASSWORD"],
        "project_name":      os.environ["OS_PROJECT_NAME"],
        "project_domain_id": "default",  # OS_PROJECT_DOMAIN_ID
        "user_domain_id":    "default"   # OS_USER_DOMAIN_NAME fails; case-dependent
    }

    return client.Client(session=session.Session(auth=identity.Password(**creds)))

if __name__ == "__main__":
    prefix  = "ch12_test"
    neutron = _neutron()

    # Get the externally routed network
    public = neutron.list_networks(retrieve_all=True, **{
        "router:external": True
    })["networks"][0]

    # Create router with an external gateway to the public network
    router = neutron.create_router({"router": {
        "name":           f"{prefix}-router",
        "admin_state_up": True,
        "external_gateway_info": {
            "network_id": public["id"]
        }
    }})["router"]

    # Create network and subnet
    network = neutron.create_network({"network": {
        "name":           f"{prefix}-network",
        "admin_state_up": True
    }})["network"]

    subnet = neutron.create_subnet({"subnets": [{
        "name":       f"{prefix}-subnet",
        "network_id": network["id"],
        "ip_version": 4,
        "cidr":       "10.1.0.1/24"
    }]})["subnets"][0]

    # Attach router to subnet through interface
    interface = neutron.add_interface_router(router["id"], {
        "subnet_id": subnet["id"]
    })

    print(f"""\
# Network created; destroy (in this order):
openstack router remove port {router['id']} {interface['port_id']}
openstack router delete {router['id']}
openstack subnet delete {subnet['id']}
openstack network delete {network['id']}""")