OpenStack Networking (Neutron) Specifications
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neutron-specs/specs/train/improve-extraroute-api.rst

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Improve Extraroute API

https://bugs.launchpad.net/neutron/+bug/1826396

As discussed in an openstack-discuss thread we could improve the extraroute API to better support Neutron API clients, especially Heat.

Problem Description

The first problem is that the current extraroute API does not allow atomic additions/deletions of particular routing table entries. In the current API the routes attribute of a router (containing all routing table entries) must be updated at once. Therefore additions and deletions must be performed on the client side. Therefore multiple clients race to update the routes attribute and updates may get lost.

This problem can be easily (but nondeterministically) reproduced by a simple HOT template as included in the References section below.

$ openstack stack create --wait -t extraroute-concurrent.yaml stack0
$ openstack stack resource list stack0 --filter name=router0 -f value -c physical_resource_id \
  | xargs -r openstack router show -f value -c routes

The second problem perceived by programmatic users of the Neutron API is that the ownership of extra routes cannot be expressed because they don't have unique identifiers. For example consider two Heat stacks (or any other user of Neutron's API) needing and therefore creating the same extra route. When one of them is deleted the extra route gets deleted for both unless we have a way to track multiple needs for the same extra route. Since addressing the second problem would involve changing the conceptual abstraction of an extra route this problem is not addressed in this specification.

Proposed Change

This RFE proposes to expose the extraroute functionality of Neutron in a new way beyond the current 'routes' attribute of routers.

Introduce a new API extension: extraroutes-atomic

PUT /v2.0/routers/{router_id}/add_extraroutes

[ { "destination": "179.24.1.0/24",
    "nexthop": "172.24.3.99" },
  ...
]
PUT /v2.0/routers/{router_id}/remove_extraroutes

[ { "destination": "179.24.1.0/24",
    "nexthop": "172.24.3.99" },
  ...
]

Partial failures are not allowed. If the addition or removal of any routing table entry fails then the whole update is reverted.

If a routing table entry to be added (removed) is already present (missing) that is not an error, but considered a successful update.

Handling of duplicate and overlapping routes is not changed from the current behavior. That is exact duplicates are rejected, but overlapping routes are allowed.

Deleting a router cascades to deleting all extra routes of that router.

The DB and OVO layer in Neutron is ready for this change, the routes attribute is is already de-composed to its own table:

mysql> describe routerroutes;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| destination | varchar(64) | NO   | PRI | NULL    |       |
| nexthop     | varchar(64) | NO   | PRI | NULL    |       |
| router_id   | varchar(36) | NO   | PRI | NULL    |       |
+-------------+-------------+------+-----+---------+-------+

Further changes included:

  • Documentation: api-ref.
  • Unit tests.
  • Tempest test in neutron-tempest-plugin.
  • Adapt python-neutronclient.
  • Adapt openstackclient.
  • Adapt openstacksdk.
  • I also hope to improve Heat's OS::Neutron::Extraroute resource building on this work, but that will be described in its own Heat blueprint.

Deprecations

As soon as the new API is merged direct updates to the 'routes' attribute of a router are deprecated, but keeping in line with the long standing Neutron tradition of not making backward incompatible API changes the old extraroutes extension is not removed.

Other Impact

No impact expected on upgrades. No impact expected on configuration. No impact expected on RPC.

Alternatives

Compare and Swap

Neutron has compare-and-swap API update logic. However using that to solve this problem is awkward on the client side (retry until success if the routes attibute change while the client edited it). Plus as the number of racing clients grow use of the compare-and-swap API is going to generate unnecessary load on API as update requests must be thrown away and retried.

Additionally current client code bases do not have support built in for compare-and-swap operations.

For other alternatives please see the review discussion of this specification.

References

extraroute-concurrent.yaml

description: test of extraroute concurrency
heat_template_version: 2015-04-30

resources:

  net0:
    type: OS::Neutron::Net

  subnet0:
    type: OS::Neutron::Subnet
    properties:
      network: { get_resource: net0 }
      cidr: 10.0.0.0/24

  router0:
    type: OS::Neutron::Router

  routerinterface0:
    type: OS::Neutron::RouterInterface
    properties:
      router: { get_resource: router0 }
      subnet: { get_resource: subnet0 }

  extraroute0:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.0.0/24
      nexthop: 10.0.0.10
      router_id: { get_resource: router0 }

  extraroute1:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.1.0/24
      nexthop: 10.0.0.11
      router_id: { get_resource: router0 }

  extraroute2:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.2.0/24
      nexthop: 10.0.0.12
      router_id: { get_resource: router0 }

  extraroute3:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.3.0/24
      nexthop: 10.0.0.13
      router_id: { get_resource: router0 }

  extraroute4:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.4.0/24
      nexthop: 10.0.0.14
      router_id: { get_resource: router0 }

  extraroute5:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.5.0/24
      nexthop: 10.0.0.15
      router_id: { get_resource: router0 }

  extraroute6:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.6.0/24
      nexthop: 10.0.0.16
      router_id: { get_resource: router0 }

  extraroute7:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.7.0/24
      nexthop: 10.0.0.17
      router_id: { get_resource: router0 }

  extraroute8:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.8.0/24
      nexthop: 10.0.0.18
      router_id: { get_resource: router0 }

  extraroute9:
    type: OS::Neutron::ExtraRoute
    properties:
      destination: 10.1.9.0/24
      nexthop: 10.0.0.19
      router_id: { get_resource: router0 }