Availability zones
An availability zone groups network nodes that run services like
DHCP, L3, FW, and others. It is defined as an agent’s attribute on the
network node. This allows users to associate an availability zone with
their resources so that the resources get high availability.
Use case
An availability zone is used to make network resources highly
available. The operators group the nodes that are attached to different
power sources under separate availability zones and configure scheduling
for resources with high availability so that they are scheduled on
different availability zones.
Required extensions
The core plug-in must support the availability_zone
extension. The core plug-in also must support the
network_availability_zone extension to schedule a network
according to availability zones. The Ml2Plugin supports it.
The router service plug-in must support the
router_availability_zone extension to schedule a router
according to the availability zones. The L3RouterPlugin
supports it.
$ openstack extension list --network -c Alias -c Name
+---------------------------+---------------------------+
| Name | Alias |
+---------------------------+---------------------------+
...
| Network Availability Zone | network_availability_zone |
...
| Availability Zone | availability_zone |
...
| Router Availability Zone | router_availability_zone |
...
+---------------------------+---------------------------+Availability zone of agents
The availability_zone attribute can be defined in
dhcp-agent and l3-agent. To define an
availability zone for each agent, set the value into
[AGENT] section of /etc/neutron/dhcp_agent.ini
or /etc/neutron/l3_agent.ini:
[AGENT]
availability_zone = zone-1To confirm the agent’s availability zone:
$ openstack network agent show 116cc128-4398-49af-a4ed-3e95494cd5fc
+---------------------+---------------------------------------------------+
| Field | Value |
+---------------------+---------------------------------------------------+
| admin_state_up | UP |
| agent_type | DHCP agent |
| alive | True |
| availability_zone | zone-1 |
| binary | neutron-dhcp-agent |
| configurations | dhcp_driver='neutron.agent.linux.dhcp.Dnsmasq', |
| | dhcp_lease_duration='86400', |
| | log_agent_heartbeats='False', networks='2', |
| | notifies_port_ready='True', ports='6', subnets='4 |
| created_at | 2016-12-14 00:25:54 |
| description | None |
| heartbeat_timestamp | 2016-12-14 06:20:24 |
| host | ankur-desktop |
| id | 116cc128-4398-49af-a4ed-3e95494cd5fc |
| started_at | 2016-12-14 00:25:54 |
| topic | dhcp_agent |
+---------------------+---------------------------------------------------+
$ openstack network agent show 9632309a-2aa4-4304-8603-c4de02c4a55f
+---------------------+-------------------------------------------------+
| Field | Value |
+---------------------+-------------------------------------------------+
| admin_state_up | UP |
| agent_type | L3 agent |
| alive | True |
| availability_zone | zone-1 |
| binary | neutron-l3-agent |
| configurations | agent_mode='legacy', ex_gw_ports='2', |
| | floating_ips='0', |
| | handle_internal_only_routers='True', |
| | interface_driver='openvswitch', interfaces='4', |
| | log_agent_heartbeats='False', routers='2' |
| created_at | 2016-12-14 00:25:58 |
| description | None |
| heartbeat_timestamp | 2016-12-14 06:20:28 |
| host | ankur-desktop |
| id | 9632309a-2aa4-4304-8603-c4de02c4a55f |
| started_at | 2016-12-14 00:25:58 |
| topic | l3_agent |
+---------------------+-------------------------------------------------+Availability zone related
attributes
The following attributes are added into network and router:
| Attribute name | Access | Required | Input type | Description |
|---|---|---|---|---|
| availability_zone_hints | RW(POST only) | No | list of string | availability zone candidates for the resource |
| availability_zones | RO | N/A | list of string | availability zones for the resource |
Use availability_zone_hints to specify the zone in which
the resource is hosted:
$ openstack network create --availability-zone-hint zone-1 \
--availability-zone-hint zone-2 net1
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | zone-1 |
| | zone-2 |
| availability_zones | |
| created_at | 2016-12-14T06:23:36Z |
| description | |
| headers | |
| id | ad88e059-e7fa-4cf7-8857-6731a2a3a554 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| mtu | 1450 |
| name | net1 |
| port_security_enabled | True |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c |
| provider:network_type | vxlan |
| provider:physical_network | None |
| provider:segmentation_id | 77 |
| revision_number | 3 |
| router:external | Internal |
| shared | False |
| status | ACTIVE |
| subnets | |
| tags | [] |
| updated_at | 2016-12-14T06:23:37Z |
+---------------------------+--------------------------------------+$ openstack router create --ha --availability-zone-hint zone-1 \
--availability-zone-hint zone-2 router1
+-------------------------+--------------------------------------+
| Field | Value |
+-------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | zone-1 |
| | zone-2 |
| availability_zones | |
| created_at | 2016-12-14T06:25:40Z |
| description | |
| distributed | False |
| external_gateway_info | null |
| flavor_id | None |
| ha | False |
| headers | |
| id | ced10262-6cfe-47c1-8847-cd64276a868c |
| name | router1 |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c |
| revision_number | 3 |
| routes | |
| status | ACTIVE |
| tags | [] |
| updated_at | 2016-12-14T06:25:40Z |
+-------------------------+--------------------------------------+Availability zone is selected from
default_availability_zones in
/etc/neutron/neutron.conf if a resource is created without
availability_zone_hints:
default_availability_zones = zone-1,zone-2To confirm the availability zone defined by the system:
$ openstack availability zone list
+-----------+-------------+
| Zone Name | Zone Status |
+-----------+-------------+
| zone-1 | available |
| zone-2 | available |
| zone-1 | available |
| zone-2 | available |
+-----------+-------------+Look at the availability_zones attribute of each
resource to confirm in which zone the resource is hosted:
$ openstack network show net1
+---------------------------+--------------------------------------+
| Field | Value |
+---------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | zone-1 |
| | zone-2 |
| availability_zones | zone-1 |
| | zone-2 |
| created_at | 2016-12-14T06:23:36Z |
| description | |
| headers | |
| id | ad88e059-e7fa-4cf7-8857-6731a2a3a554 |
| ipv4_address_scope | None |
| ipv6_address_scope | None |
| mtu | 1450 |
| name | net1 |
| port_security_enabled | True |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c |
| provider:network_type | vxlan |
| provider:physical_network | None |
| provider:segmentation_id | 77 |
| revision_number | 3 |
| router:external | Internal |
| shared | False |
| status | ACTIVE |
| subnets | |
| tags | [] |
| updated_at | 2016-12-14T06:23:37Z |
+---------------------------+--------------------------------------+$ openstack router show router1
+-------------------------+--------------------------------------+
| Field | Value |
+-------------------------+--------------------------------------+
| admin_state_up | UP |
| availability_zone_hints | zone-1 |
| | zone-2 |
| availability_zones | zone-1 |
| | zone-2 |
| created_at | 2016-12-14T06:25:40Z |
| description | |
| distributed | False |
| external_gateway_info | null |
| flavor_id | None |
| ha | False |
| headers | |
| id | ced10262-6cfe-47c1-8847-cd64276a868c |
| name | router1 |
| project_id | cfd1889ac7d64ad891d4f20aef9f8d7c |
| revision_number | 3 |
| routes | |
| status | ACTIVE |
| tags | [] |
| updated_at | 2016-12-14T06:25:40Z |
+-------------------------+--------------------------------------+Note
The availability_zones attribute does not have a value
until the resource is scheduled. Once the Networking service schedules
the resource to zones according to availability_zone_hints,
availability_zones shows in which zone the resource is
hosted practically. The availability_zones may not match
availability_zone_hints. For example, even if you specify a
zone with availability_zone_hints, all agents of the zone
may be dead before the resource is scheduled. In general, they should
match, unless there are failures or there is no capacity left in the
zone requested.
Availability zone aware
scheduler
Network scheduler
Set AZAwareWeightScheduler to
network_scheduler_driver in
/etc/neutron/neutron.conf so that the Networking service
schedules a network according to the availability zone:
network_scheduler_driver = neutron.scheduler.dhcp_agent_scheduler.AZAwareWeightScheduler
dhcp_load_type = networksThe Networking service schedules a network to one of the agents
within the selected zone as with WeightScheduler. In this
case, scheduler refers to dhcp_load_type as well.
Router scheduler
Set AZLeastRoutersScheduler to
router_scheduler_driver in file
/etc/neutron/neutron.conf so that the Networking service
schedules a router according to the availability zone:
router_scheduler_driver = neutron.scheduler.l3_agent_scheduler.AZLeastRoutersSchedulerThe Networking service schedules a router to one of the agents within
the selected zone as with LeastRouterScheduler.
Achieving
high availability with availability zone
Although, the Networking service provides high availability for
routers and high availability and fault tolerance for networks’ DHCP
services, availability zones provide an extra layer of protection by
segmenting a Networking service deployment in isolated failure domains.
By deploying HA nodes across different availability zones, it is
guaranteed that network services remain available in face of zone-wide
failures that affect the deployment.
This section explains how to get high availability with the
availability zone for L3 and DHCP. You should naturally set above
configuration options for the availability zone.
L3 high availability
Set the following configuration options in file
/etc/neutron/neutron.conf so that you get L3 high
availability.
l3_ha = True
max_l3_agents_per_router = 3HA routers are created on availability zones you selected when
creating the router.
DHCP high availability
Set the following configuration options in file
/etc/neutron/neutron.conf so that you get DHCP high
availability.
dhcp_agents_per_network = 2DHCP services are created on availability zones you selected when
creating the network.