auto_allocate_network is not called when external shared network exists

[Yushiro FURUKAWA]

When I try to boot an instance with '--nic auto', a network isn't created
automatically. In neutron side, in order to automatically allocate
network/subnet/router, following network is necessary in advance:

    * router:external is True(it means an external network)
    * is_default is True
    * subnet is associated

However, if I prepared above default network, nova doesn't call
'_can_auto_allocate_network'[1]. As a result, the VM instance is attached that
external network.(not generated a network automatically)

[1] https://github.com/openstack/nova/blob/master/nova/network/neutronv2/api.py#L1532

[Steps to reproduce]
1. Delete all network/subnet/port/router in neutron

2. Try to create an instance
  $ nova boot --flavor 1 --image 198384a2-9ece-4d24-a509-4ce02f183b63 vm1 --nic auto

ERROR (BadRequest): Unable to automatically allocate a network for project c8607bb7e4334b43aede76831b91ca03 (HTTP 400) (Request-ID: req-2d4088f6-d9aa-492d-a645-02327a058a47)
In n-api.log, we can see following error message:
Error message: {"NeutronError": {"message": "Deployment error: No default router:external network.", "type": "AutoAllocationFailure", "detail": ""}}

3. I see. OK, let's create default external network(router:external)
  $ neutron net-create public --is_default --router:external --shared
  $ neutron subnet-create public --subnetpool a811bf33-dacc-42b9-b44a-d424f37023df

4. Try it again 'nova boot'
  $ nova boot --flavor 1 --image 198384a2-9ece-4d24-a509-4ce02f183b63 vm1 --nic auto

5. You can check the result with 'nova list'
  $ nova list
+--------------------------------------+------+--------+------------+-------------+-----------------+
| ID | Name | Status | Task State | Power State | Networks |
+--------------------------------------+------+--------+------------+-------------+-----------------+
| 4e83f9d0-acbf-4440-8563-17dd6ec0cde5 | vm1 | BUILD | spawning | NOSTATE | public=10.0.0.9 |
+--------------------------------------+------+--------+------------+-------------+-----------------+

[Matt Riedemann (mriedem)]

You're getting the public external network because you marked it as shared=True so it's pulled in here:

https://github.com/openstack/nova/blob/a67af1f110f160861f5cbbff987766c46d60198a/nova/network/neutronv2/api.py#L343

And you pass this check for the external shared network on the compute:

https://github.com/openstack/nova/blob/a67af1f110f160861f5cbbff987766c46d60198a/nova/network/neutronv2/api.py#L466

So the port for the server gets created in that network. I'm not sure what else you expect to happen here.

[Yushiro FURUKAWA (y-furukawa-2)]

Hi Matt, thanks for your reply. I understood that following condition should be satisfied to run auto_allocate_topology.

1. There is no networks in a target project(ex. "demo" project)
2. There is a network in different project with following conditions(ex. in "admin" project:
    * "router:external" is True(it is equal to external network)
    * "is_default" is True
    * A subnet is associated with the network

After that, I executed "nova boot" with "--nic auto" into "demo" project. As a result, auto_allocated_network is generated.

[Yushiro FURUKAWA (y-furukawa-2)]

^^^
    * "shared" is False