Quality of Service (QoS)

updated: 2020-07-28 12:10

Quality of Service (QoS)¶

QoS is defined as the ability to guarantee certain network requirements like bandwidth, latency, jitter, and reliability in order to satisfy a Service Level Agreement (SLA) between an application provider and end users.

Network devices such as switches and routers can mark traffic so that it is handled with a higher priority to fulfill the QoS conditions agreed under the SLA. In other cases, certain network traffic such as Voice over IP (VoIP) and video streaming needs to be transmitted with minimal bandwidth constraints. On a system without network QoS management, all traffic will be transmitted in a “best-effort” manner making it impossible to guarantee service delivery to customers.

QoS is an advanced service plug-in. QoS is decoupled from the rest of the OpenStack Networking code on multiple levels and it is available through the ml2 extension driver.

Details about the DB models, API extension, and use cases are out of the scope of this guide but can be found in the Neutron QoS specification.

Supported QoS rule types¶

Any plug-in or ml2 mechanism driver can claim support for some QoS rule types by providing a plug-in/driver class property called supported_qos_rule_types that returns a list of strings that correspond to QoS rule types.

The following table shows the Networking back ends, QoS supported rules, and traffic directions (from the VM point of view).

**Networking back ends, supported rules, and traffic direction**¶
Rule back end	Open vSwitch	SR-IOV	Linux bridge
Bandwidth limit	EgressIngress	Egress (1)	EgressIngress
Minimum bandwidth		Egress
DSCP marking	Egress		Egress

Note

Max burst parameter is skipped because it is not supported by the IP tool.

In the most simple case, the property can be represented by a simple Python list defined on the class.

For an ml2 plug-in, the list of supported QoS rule types and parameters is defined as a common subset of rules supported by all active mechanism drivers. A QoS rule is always attached to a QoS policy. When a rule is created or updated:

The QoS plug-in will check if this rule and parameters are supported by any active mechanism driver if the QoS policy is not attached to any port or network.
The QoS plug-in will check if this rule and parameters are supported by the mechanism drivers managing those ports if the QoS policy is attached to any port or network.

Valid DSCP Marks¶

Valid DSCP mark values are even numbers between 0 and 56, except 2-6, 42, 44, and 50-54. The full list of valid DSCP marks is:

0, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 46, 48, 56

Configuration¶

To enable the service, follow the steps below:

On network nodes:

Add the QoS service to the service_plugins setting in /etc/neutron/neutron.conf. For example:

service_plugins = \
neutron.services.l3_router.l3_router_plugin.L3RouterPlugin,
neutron.services.metering.metering_plugin.MeteringPlugin,
neutron.services.qos.qos_plugin.QoSPlugin

Optionally, set the needed notification_drivers in the [qos] section in /etc/neutron/neutron.conf (message_queue is the default).
In /etc/neutron/plugins/ml2/ml2_conf.ini, add qos to extension_drivers in the [ml2] section. For example:
```
[ml2]
extension_drivers = port_security, qos
```
If the Open vSwitch agent is being used, set extensions to qos in the [agent] section of /etc/neutron/plugins/ml2/openvswitch_agent.ini. For example:
```
[agent]
extensions = qos
```

On compute nodes:

In /etc/neutron/plugins/ml2/openvswitch_agent.ini, add qos to the extensions setting in the [agent] section. For example:
```
[agent]
extensions = qos
```

Note

QoS currently works with ml2 only (SR-IOV, Open vSwitch, and linuxbridge are drivers that are enabled for QoS in Mitaka release).

Trusted projects policy.json configuration¶

If projects are trusted to administrate their own QoS policies in your cloud, neutron’s file policy.json can be modified to allow this.

Modify /etc/neutron/policy.json policy entries as follows:

"get_policy": "rule:regular_user",
"create_policy": "rule:regular_user",
"update_policy": "rule:regular_user",
"delete_policy": "rule:regular_user",
"get_rule_type": "rule:regular_user",

To enable bandwidth limit rule:

"get_policy_bandwidth_limit_rule": "rule:regular_user",
"create_policy_bandwidth_limit_rule": "rule:regular_user",
"delete_policy_bandwidth_limit_rule": "rule:regular_user",
"update_policy_bandwidth_limit_rule": "rule:regular_user",

To enable DSCP marking rule:

"get_policy_dscp_marking_rule": "rule:regular_user",
"create_dscp_marking_rule": "rule:regular_user",
"delete_dscp_marking_rule": "rule:regular_user",
"update_dscp_marking_rule": "rule:regular_user",

To enable minimum bandwidth rule:

"get_policy_minimum_bandwidth_rule": "rule:regular_user",
"create_policy_minimum_bandwidth_rule": "rule:regular_user",
"delete_policy_minimum_bandwidth_rule": "rule:regular_user",
"update_policy_minimum_bandwidth_rule": "rule:regular_user",

User workflow¶

QoS policies are only created by admins with the default policy.json. Therefore, you should have the cloud operator set them up on behalf of the cloud projects.

If projects are trusted to create their own policies, check the trusted projects policy.json configuration section.

First, create a QoS policy and its bandwidth limit rule:

$ openstack network qos policy create bw-limiter

Created a new policy:
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| description |                                      |
| id          | 5df855e9-a833-49a3-9c82-c0839a5f103f |
| is_default  | False                                |
| name        | qos1                                 |
| project_id  | 4db7c1ed114a4a7fb0f077148155c500     |
| rules       | []                                   |
| shared      | False                                |
+-------------+--------------------------------------+

$ openstack network qos rule create --type bandwidth-limit --max-kbps 3000 \
    --max-burst-kbits 300 --egress bw-limiter

Created a new bandwidth_limit_rule:
+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| direction      | egress                               |
| id             | 92ceb52f-170f-49d0-9528-976e2fee2d6f |
| max_burst_kbps | 300                                  |
| max_kbps       | 3000                                 |
+----------------+--------------------------------------+

Note

The QoS implementation requires a burst value to ensure proper behavior of bandwidth limit rules in the Open vSwitch and Linux bridge agents. If you do not provide a value, it defaults to 80% of the bandwidth limit which works for typical TCP traffic.

Second, associate the created policy with an existing neutron port. In order to do this, user extracts the port id to be associated to the already created policy. In the next example, we will assign the bw-limiter policy to the VM with IP address 192.0.2.1.

$ openstack port list

+--------------------------------------+-----------------------------------+
| ID                                   | Fixed IP Addresses                |
+--------------------------------------+-----------------------------------+
| 0271d1d9-1b16-4410-bd74-82cdf6dcb5b3 | { ... , "ip_address": "192.0.2.1"}|
| 88101e57-76fa-4d12-b0e0-4fc7634b874a | { ... , "ip_address": "192.0.2.3"}|
| e04aab6a-5c6c-4bd9-a600-33333551a668 | { ... , "ip_address": "192.0.2.2"}|
+--------------------------------------+-----------------------------------+

$ openstack port set --qos-policy bw-limiter \
    88101e57-76fa-4d12-b0e0-4fc7634b874a
Updated port: 88101e57-76fa-4d12-b0e0-4fc7634b874a

In order to detach a port from the QoS policy, simply update again the port configuration.

$ openstack port unset --no-qos-policy 88101e57-76fa-4d12-b0e0-4fc7634b874a
Updated port: 88101e57-76fa-4d12-b0e0-4fc7634b874a

Ports can be created with a policy attached to them too.

$ openstack port create --qos-policy bw-limiter --network private port1

Created a new port:
+-----------------------+--------------------------------------------------+
| Field                 | Value                                            |
+-----------------------+--------------------------------------------------+
| admin_state_up        | UP                                               |
| allowed_address_pairs |                                                  |
| binding_host_id       |                                                  |
| binding_profile       |                                                  |
| binding_vif_details   |                                                  |
| binding_vif_type      | unbound                                          |
| binding_vnic_type     | normal                                           |
| created_at            | 2017-05-15T08:43:00Z                             |
| description           |                                                  |
| device_id             |                                                  |
| device_owner          |                                                  |
| dns_assignment        | None                                             |
| dns_name              | None                                             |
| extra_dhcp_opts       |                                                  |
| fixed_ips             | ip_address='10.0.10.4', subnet_id='292f8c1e-...' |
| id                    | f51562ee-da8d-42de-9578-f6f5cb248226             |
| ip_address            | None                                             |
| mac_address           | fa:16:3e:d9:f2:ba                                |
| name                  | port1                                            |
| network_id            | 55dc2f70-0f92-4002-b343-ca34277b0234             |
| option_name           | None                                             |
| option_value          | None                                             |
| port_security_enabled | False                                            |
| project_id            | 4db7c1ed114a4a7fb0f077148155c500                 |
| qos_policy_id         | 5df855e9-a833-49a3-9c82-c0839a5f103f             |
| revision_number       | 6                                                |
| security_group_ids    | 0531cc1a-19d1-4cc7-ada5-49f8b08245be             |
| status                | DOWN                                             |
| subnet_id             | None                                             |
| updated_at            | 2017-05-15T08:43:00Z                             |
+-----------------------+--------------------------------------------------+

You can attach networks to a QoS policy. The meaning of this is that any compute port connected to the network will use the network policy by default unless the port has a specific policy attached to it. Internal network owned ports like DHCP and internal router ports are excluded from network policy application.

In order to attach a QoS policy to a network, update an existing network, or initially create the network attached to the policy.

$ openstack network set --qos-policy bw-limiter private
Updated network: private

Note

Configuring the proper burst value is very important. If the burst value is set too low, bandwidth usage will be throttled even with a proper bandwidth limit setting. This issue is discussed in various documentation sources, for example in Juniper’s documentation. Burst value for TCP traffic can be set as 80% of desired bandwidth limit value. For example, if the bandwidth limit is set to 1000kbps then enough burst value will be 800kbit. If the configured burst value is too low, achieved bandwidth limit will be lower than expected. If the configured burst value is too high, too few packets could be limited and achieved bandwidth limit would be higher than expected.

Each project can have at most one default QoS policy, although it is not mandatory. If a default QoS policy is defined, all new networks created within this project will have this policy assigned, as long as no other QoS policy is explicitly attached during the creation process. If the default QoS policy is unset, no change to existing networks will be made.

In order to set a QoS policy as default, the parameter --default must be used. To unset this QoS policy as default, the parameter --no-default must be used.

$ openstack network qos policy create --default bw-limiter

Created a new policy:
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| description |                                      |
| id          | 5df855e9-a833-49a3-9c82-c0839a5f103f |
| is_default  | True                                 |
| name        | qos1                                 |
| project_id  | 4db7c1ed114a4a7fb0f077148155c500     |
| rules       | []                                   |
| shared      | False                                |
+-------------+--------------------------------------+

$ openstack network qos policy set --no-default bw-limiter

Created a new policy:
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| description |                                      |
| id          | 5df855e9-a833-49a3-9c82-c0839a5f103f |
| is_default  | False                                |
| name        | qos1                                 |
| project_id  | 4db7c1ed114a4a7fb0f077148155c500     |
| rules       | []                                   |
| shared      | False                                |
+-------------+--------------------------------------+

Administrator enforcement¶

Administrators are able to enforce policies on project ports or networks. As long as the policy is not shared, the project is not be able to detach any policy attached to a network or port.

If the policy is shared, the project is able to attach or detach such policy from its own ports and networks.

Rule modification¶

You can modify rules at runtime. Rule modifications will be propagated to any attached port.

$ openstack network qos rule set --max-kbps 2000 --max-burst-kbps 200 \
    --ingress bw-limiter 92ceb52f-170f-49d0-9528-976e2fee2d6f
Updated bandwidth_limit_rule: 92ceb52f-170f-49d0-9528-976e2fee2d6f

$ openstack network qos rule show \
    bw-limiter 92ceb52f-170f-49d0-9528-976e2fee2d6f

+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| direction      | ingress                              |
| id             | 92ceb52f-170f-49d0-9528-976e2fee2d6f |
| max_burst_kbps | 200                                  |
| max_kbps       | 2000                                 |
+----------------+--------------------------------------+

Just like with bandwidth limiting, create a policy for DSCP marking rule:

$ openstack network qos policy create dscp-marking

+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| description |                                      |
| id          | d1f90c76-fbe8-4d6f-bb87-a9aea997ed1e |
| is_default  | False                                |
| name        | dscp-marking                         |
| project_id  | 4db7c1ed114a4a7fb0f077148155c500     |
| rules       | []                                   |
| shared      | False                                |
+-------------+--------------------------------------+

You can create, update, list, delete, and show DSCP markings with the neutron client:

$ openstack network qos rule create --type dscp-marking --dscp-mark 26 \
    dscp-marking

Created a new dscp marking rule
+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| id             | 115e4f70-8034-4176-8fe9-2c47f8878a7d |
| dscp_mark      | 26                                   |
+----------------+--------------------------------------+

$ openstack network qos rule set --dscp-mark 22 \
    dscp-marking 115e4f70-8034-4176-8fe9-2c47f8878a7d
Updated dscp_rule: 115e4f70-8034-4176-8fe9-2c47f8878a7d

$ openstack network qos rule list dscp-marking

+--------------------------------------+----------------------------------+
| ID                                   | DSCP Mark                        |
+--------------------------------------+----------------------------------+
| 115e4f70-8034-4176-8fe9-2c47f8878a7d | 22                               |
+--------------------------------------+----------------------------------+

$ openstack network qos rule show \
    dscp-marking 115e4f70-8034-4176-8fe9-2c47f8878a7d

+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| id             | 115e4f70-8034-4176-8fe9-2c47f8878a7d |
| dscp_mark      | 22                                   |
+----------------+--------------------------------------+

$ openstack network qos rule delete \
    dscp-marking 115e4f70-8034-4176-8fe9-2c47f8878a7d
  Deleted dscp_rule: 115e4f70-8034-4176-8fe9-2c47f8878a7d

You can also include minimum bandwidth rules in your policy:

$ openstack network qos policy create bandwidth-control
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| description |                                      |
| id          | 8491547e-add1-4c6c-a50e-42121237256c |
| is_default  | False                                |
| name        | bandwidth-control                    |
| project_id  | 7cc5a84e415d48e69d2b06aa67b317d8     |
| rules       | []                                   |
| shared      | False                                |
+-------------+--------------------------------------+

$ openstack network qos rule create \
  --type minimum-bandwidth --min-kbps 1000 --egress bandwidth-control
+------------+--------------------------------------+
| Field      | Value                                |
+------------+--------------------------------------+
| direction  | egress                               |
| id         | da858b32-44bc-43c9-b92b-cf6e2fa836ab |
| min_kbps   | 1000                                 |
| name       | None                                 |
| project_id |                                      |
+------------+--------------------------------------+

A policy with a minimum bandwidth ensures best efforts are made to provide no less than the specified bandwidth to each port on which the rule is applied. However, as this feature is not yet integrated with the Compute scheduler, minimum bandwidth cannot be guaranteed.

It is also possible to combine several rules in one policy:

$ openstack network qos rule create --type bandwidth-limit \
    --max-kbps 50000 --max-burst-kbits 50000 bandwidth-control
+----------------+--------------------------------------+
| Field          | Value                                |
+----------------+--------------------------------------+
| id             | 0db48906-a762-4d32-8694-3f65214c34a6 |
| max_burst_kbps | 50000                                |
| max_kbps       | 50000                                |
| name           | None                                 |
| project_id     |                                      |
+----------------+--------------------------------------+

$ openstack network qos policy show bandwidth-control
+-------------+-------------------------------------------------------------------+
| Field       | Value                                                             |
+-------------+-------------------------------------------------------------------+
| description |                                                                   |
| id          | 8491547e-add1-4c6c-a50e-42121237256c                              |
| is_default  | False                                                             |
| name        | bandwidth-control                                                 |
| project_id  | 7cc5a84e415d48e69d2b06aa67b317d8                                  |
| rules       | [{u'max_kbps': 50000, u'type': u'bandwidth_limit',                |
|             |   u'id': u'0db48906-a762-4d32-8694-3f65214c34a6',                 |
|             |   u'max_burst_kbps': 50000,                                       |
|             |   u'qos_policy_id': u'8491547e-add1-4c6c-a50e-42121237256c'},     |
|             |  {u'direction':                                                   |
|             |   u'egress', u'min_kbps': 1000, u'type': u'minimum_bandwidth',    |
|             |   u'id': u'da858b32-44bc-43c9-b92b-cf6e2fa836ab',                 |
|             |   u'qos_policy_id': u'8491547e-add1-4c6c-a50e-42121237256c'}]     |
| shared      | False                                                             |
+-------------+-------------------------------------------------------------------+

updated: 2020-07-28 12:10

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