Differece behavior about enable subnet service types scenario

[zhaobo]

Repro:
1. create a net and a subnet 'A-compute-nova' with service_types "compute:nova"
2. exec neutron port-create only specified the network ID/name.
   This will return "No valid service subnet for the given device owner."
   We only can create port with device_owner "compute:nova"
3. create another subnet 'B-None', no specify the service_types.
Then create port with device_owner=compute:nova and fixed_ip from 'B-None', it create successful.
But why not raise the error just the same with step 2? As we wish the IPs of port always allocate from the subnet which service_type is 'compute:nova'.

[Brian Haley (brian-haley)]

Yes, fixed_ip always has precedence today, but I think it's correct to check the service type if we have the information.

[Miguel Lavalle (minsel)]

This is not a bug. Please read this section of the documentation: https://docs.openstack.org/neutron/latest/admin/config-service-subnets.html#operation. Bottom line, a subnet with no service type is compatible with ports of any device owner. As a consequence, the following use case is perfectly valid:

1) The network has one subnet without service type
2) The network has one or more subnets with service types
3) The user wants to create a port on the subnet without service type with a device owner that matches the service type of one of the other subnets

Since a subnet without service type is compatible with any device owner, the port creation should succeed. This bug proposes to forbid it. Why? I am going to bring this bug up in the L3 subteam meeting that will take place on August 3rd at 1500 UTC in channel #openstack-meeting-3. The submitter of this bug is welcome to join the discussion

[Brian Haley (brian-haley)]

Miguel - yes, I probably even wrote part of that document :)

I was maybe thinking of an edge case where there were no more IPs matching the service-type, but then we did document that as well:

"During IP allocation, the IPAM driver returns an address from a subnet with a service type matching the port device owner. If no subnets match, or all matching subnets lack available IP addresses, the IPAM driver attempts to use a subnet without any service types to preserve compatibility."

That covers this bug - port with one device_owner value can have an IP in a subnet with the None service-type. As long as you can't allocate an IP from a subnet of another non-None service-type this bug is probably invalid then.

[Miguel Lavalle (minsel)]

This bug was discussed today during the L3 subteam meeting and the agreement was that is is invalid. Please see discussion log here: http://eavesdrop.openstack.org/meetings/neutron_l3/2017/neutron_l3.2017-08-03-15.00.log.html#l-90

[OpenStack Infra (hudson-openstack)]

Change abandoned by ZhaoBo (<email address hidden>) on branch: master
Review: https://review.openstack.org/488944

[zhaobo (zhaobo6)]

Thank you! @Miguel @Brian。
Thanks for the discuss about this bug. This is more clear about this feature behavior. Thanks.