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-1
To 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', |
| | external_network_bridge='', floating_ips='0', |
| | gateway_external_network_id='', |
| | 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 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 = networks
The 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.AZLeastRoutersScheduler
The 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 = 3
HA 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 = 2
DHCP services are created on availability zones you selected when creating the network.
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