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[Bug 1695740] [NEW] Segments, routed-networks, IPAM only usecase regression

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Harald Jensås <harald.jensas@xxxxxxxxx>
Date: Sun, 04 Jun 2017 14:04:46 -0000
Reply-to: Bug 1695740 <1695740@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx

Public bug reported:

Segments, routed-networks, IPAM only usecase regression

Code[1] will defer IP allocation if host is not specified.

Issues:
a) This breaks the use case where Neutron is used for IPAM only with
routed network.
b) A user can no longer create a port and specify a fixed IP, then later
bind the port without loosing the fixed-ip information.

Issue b) above is a very common pattern in Heat templates.
It is used in Heat templates examples, ref:
- https://github.com/openstack/heat-templates/blob/master/hot/servers_in_new_neutron_net.yaml#L77:L82
- https://github.com/openstack/heat-templates/blob/master/hot/servers_in_existing_neutron_net.yaml#L30:L46

Current behaviour with segments is that ip-allocation is deferred for _any_ port create. Deferring ip allocation if the host is not known does make sense. Before host is known the available segments are also not known and we need to wait until the scheduler has picked a host and nova adds binding:host_id. However...
... this does not make sense if the subnet or fixed-ip is specified in the port create request. In this case we should not defer allocation, the user specified exactly what they want and it is known where to allocate the IP.

When / If this port is later bound to a host, an error will be raised if
that host does not have the correct segments. This is essentially the
same update scenario already covered in the code?[2]

When creating an instance using an existing port with and IP address,
the scheduler should take the ip-allocation data from the port provided
in the request and ensure that the instance is scheduled to a host that
is connected to the correct segment. According to nova neutron-routed-
networks spec[1] this exact use case was included.

""" Use case 2:
User has a port that has an IP address and thus is effectively
attached to a segment (but not bound to a host). He/She
provides it to nova boot. Nova will ask Neutron for the segment
to which the port is bound by getting the details of the port.
Given that segment, the scheduler should place the instance
on a compute host belonging to the corresponding aggregate. """

[1] https://github.com/openstack/neutron/blob/master/neutron/db/ipam_backend_mixin.py#L662:L700
[2] https://github.com/openstack/neutron/blob/master/neutron/db/ipam_backend_mixin.py#L769:L777
[3] https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/neutron-routed-networks.html

** Affects: neutron
Importance: Undecided
Status: New

** Tags: l3-ipam-dhcp

** Description changed:

Segments, routed-networks, IPAM only usecase regression

Code[1] will defer IP allocation if host is not specified.

- Issues:
- a) This breaks the use case where Neutron is used for IPAM only with routed network.
- b) A user can no longer create a port and specify a fixed IP, then later bind the
- port without loosing the fixed-ip information.
+ Issues:
+ a) This breaks the use case where Neutron is used for IPAM only with
+ routed network.
+ b) A user can no longer create a port and specify a fixed IP, then later
+ bind the port without loosing the fixed-ip information.

- Issue b) above is a very common pattern in Heat templates. It is used in Heat templates examples, ref:
- - https://github.com/openstack/heat-templates/blob/master/hot/servers_in_new_neutron_net.yaml#L77:L82
- - https://github.com/openstack/heat-templates/blob/master/hot/servers_in_existing_neutron_net.yaml#L30:L46
+ Issue b) above is a very common pattern in Heat templates.
+ It is used in Heat templates examples, ref:
+ - https://github.com/openstack/heat-templates/blob/master/hot/servers_in_new_neutron_net.yaml#L77:L82
+ - https://github.com/openstack/heat-templates/blob/master/hot/servers_in_existing_neutron_net.yaml#L30:L46

When / If this port is later bound to a host, an error will be raised if
that host does not have the correct segments. This is essentially the
same update scenario already covered in the code?[2]

- """ Use case 2:
- User has a port that has an IP address and thus is effectively
- attached to a segment (but not bound to a host). He/She
- provides it to nova boot. Nova will ask Neutron for the segment
- to which the port is bound by getting the details of the port.
- Given that segment, the scheduler should place the instance
- on a compute host belonging to the corresponding aggregate. """
-
+ """ Use case 2:
+ User has a port that has an IP address and thus is effectively
+ attached to a segment (but not bound to a host). He/She
+ provides it to nova boot. Nova will ask Neutron for the segment
+ to which the port is bound by getting the details of the port.
+ Given that segment, the scheduler should place the instance
+ on a compute host belonging to the corresponding aggregate. """

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https://bugs.launchpad.net/bugs/1695740

Title:
Segments, routed-networks, IPAM only usecase regression

Status in neutron:
New

Bug description:
Segments, routed-networks, IPAM only usecase regression

Code[1] will defer IP allocation if host is not specified.

When / If this port is later bound to a host, an error will be raised
if that host does not have the correct segments. This is essentially
the same update scenario already covered in the code?[2]

When creating an instance using an existing port with and IP address,
the scheduler should take the ip-allocation data from the port
provided in the request and ensure that the instance is scheduled to a
host that is connected to the correct segment. According to nova
neutron-routed-networks spec[1] this exact use case was included.

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Follow ups

[Bug 1695740] Re: Segments, routed-networks, IPAM only usecase regression
From: OpenStack Infra, 2017-06-14