Automatic allocation of network topologies

The auto-allocation feature introduced in Mitaka simplifies the procedure of setting up an external connectivity for end-users, and is also known as Get Me A Network.

Previously, a user had to configure a range of networking resources to boot a server and get access to the Internet. For example, the following steps are required:

  • Create a network

  • Create a subnet

  • Create a router

  • Uplink the router on an external network

  • Downlink the router on the previously created subnet

These steps need to be performed on each logical segment that a VM needs to be connected to, and may require networking knowledge the user might not have.

This feature is designed to automate the basic networking provisioning for projects. The steps to provision a basic network are run during instance boot, making the networking setup hands-free.

To make this possible, provide a default external network and default subnetpools (one for IPv4, or one for IPv6, or one of each) so that the Networking service can choose what to do in lieu of input. Once these are in place, users can boot their VMs without specifying any networking details. The Compute service will then use this feature automatically to wire user VMs.

Enabling the deployment for auto-allocation

To use this feature, the neutron service must have the following extensions enabled:

  • auto-allocated-topology

  • subnet_allocation

  • external-net

  • router

Before the end-user can use the auto-allocation feature, the operator must create the resources that will be used for the auto-allocated network topology creation. To perform this task, proceed with the following steps:

  1. Set up a default external network

    Setting up an external network is described in OpenStack Networking Guide. Assuming the external network to be used for the auto-allocation feature is named public, make it the default external network with the following command:

    $ openstack network set public --default

    Note

    The flag --default (and --no-default flag) is only effective with external networks and has no effects on regular (or internal) networks.

  2. Create default subnetpools

    The auto-allocation feature requires at least one default subnetpool. One for IPv4, or one for IPv6, or one of each.

    $ openstack subnet pool create --share --default \
  --pool-prefix 192.0.2.0/24 --default-prefix-length 26 \
  shared-default

  +-------------------+--------------------------------------+
  | Field             | Value                                |
  +-------------------+--------------------------------------+
  | address_scope_id  | None                                 |
  | created_at        | 2017-01-12T15:10:34Z                 |
  | default_prefixlen | 26                                   |
  | default_quota     | None                                 |
  | description       |                                      |
  | headers           |                                      |
  | id                | b41b7b9c-de57-4c19-b1c5-731985bceb7f |
  | ip_version        | 4                                    |
  | is_default        | True                                 |
  | max_prefixlen     | 32                                   |
  | min_prefixlen     | 8                                    |
  | name              | shared-default                       |
  | prefixes          | 192.0.2.0/24                         |
  | project_id        | 86acdbd1d72745fd8e8320edd7543400     |
  | revision_number   | 1                                    |
  | shared            | True                                 |
  | tags              | []                                   |
  | updated_at        | 2017-01-12T15:10:34Z                 |
  +-------------------+--------------------------------------+

$ openstack subnet pool create --share --default \
  --pool-prefix 2001:db8:8000::/48 --default-prefix-length 64 \
  default-v6

+-------------------+--------------------------------------+
| Field             | Value                                |
+-------------------+--------------------------------------+
| address_scope_id  | None                                 |
| created_at        | 2017-01-12T15:14:35Z                 |
| default_prefixlen | 64                                   |
| default_quota     | None                                 |
| description       |                                      |
| headers           |                                      |
| id                | 6f387016-17f0-4564-96ad-e34775b6ea14 |
| ip_version        | 6                                    |
| is_default        | True                                 |
| max_prefixlen     | 128                                  |
| min_prefixlen     | 64                                   |
| name              | default-v6                           |
| prefixes          | 2001:db8:8000::/48                   |
| project_id        | 86acdbd1d72745fd8e8320edd7543400     |
| revision_number   | 1                                    |
| shared            | True                                 |
| tags              | []                                   |
| updated_at        | 2017-01-12T15:14:35Z                 |
+-------------------+--------------------------------------+

Get Me A Network

In a deployment where the operator has set up the resources as described above, they can get or create their auto-allocated network topology as follows:

$ openstack network auto allocated topology create --or-show
+------------+--------------------------------------+
| Field      | Value                                |
+------------+--------------------------------------+
| id         | a380c780-d6cd-4510-a4c0-1a6ec9b85a29 |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c     |
+------------+--------------------------------------+

Note

When the --or-show option is used the command returns the topology information if it already exists, or creates it if it does not.

Operators (and users with admin role) can get or create the auto-allocated topology for a project by specifying the project ID:

$ openstack network auto allocated topology create --project \
  cfd1889ac7d64ad891d4f20aef9f8d7c --or-show
+------------+--------------------------------------+
| Field      | Value                                |
+------------+--------------------------------------+
| id         | a380c780-d6cd-4510-a4c0-1a6ec9b85a29 |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c     |
+------------+--------------------------------------+

The ID returned by this command is a network which can be used for booting a VM.

$ openstack server create --flavor m1.small --image \
  cirros-0.3.5-x86_64-uec --nic \
  net-id=8b835bfb-cae2-4acc-b53f-c16bb5f9a7d0 vm1

The auto-allocated topology for a user never changes. In practice, when a user boots a server omitting the --nic option, and there is more than one network available, the Compute service will invoke the API behind auto allocated topology create, fetch the network UUID, and pass it on during the boot process.

Alternately one can delete their auto-allocated network topology as follows:

$ openstack network auto allocated topology delete

Validating the requirements for auto-allocation

To validate that the required resources are correctly set up for auto-allocation, without actually provisioning anything, use the --check-resources option:

$ openstack network auto allocated topology create --check-resources
Deployment error: No default router:external network.

$ openstack network set public --default

$ openstack network auto allocated topology create --check-resources
Deployment error: No default subnetpools defined.

$ openstack subnet pool set shared-default --default

$ openstack network auto allocated topology create --check-resources
+---------+-------+
| Field   | Value |
+---------+-------+
| dry-run | pass  |
+---------+-------+

The validation option behaves identically for all users. However, it is considered primarily an admin or service utility since it is the operator who must set up the requirements.

Project resources created by auto-allocation

The auto-allocation feature creates one network topology in every project where it is used. The auto-allocated network topology for a project contains the following resources:

Resource

Name

network

auto_allocated_network

subnet (IPv4)

auto_allocated_subnet_v4

subnet (IPv6)

auto_allocated_subnet_v6

router

auto_allocated_router

Compatibility notes

Nova uses the auto allocated topology feature with API micro version 2.37 or later. This is because, unlike the neutron feature which was implemented in the Mitaka release, the integration for nova was completed during the Newton release cycle. Note that the CLI option --nic can be omitted regardless of the microversion used as long as there is no more than one network available to the project, in which case nova fails with a 400 error because it does not know which network to use. Furthermore, nova does not start using the feature, regardless of whether or not a user requests micro version 2.37 or later, unless all of the nova-compute services are running Newton-level code.