Only one instance of a DHCP agent is run per network

[Robert Collins]

DHCP Agent's are stateless and can run HA, but the scheduler only schedules one instance - when a network node fails (or is rebooted / has maintenance done on it) this results in user visible downtime.

See also bug 1174591 which talks about the administrative overhead of dealing with failed nodes.

[Robert Collins (lifeless)]

https://etherpad.openstack.org/HavanaBareMetalVLAN was the summit discussion about this.

[Gary Kotton (garyk)]

Hi,
By default the scheduler allocates one agent. You are then able to add additional ones.
Please see the example below:

openstack@openstack:~/devstack$ quantum dhcp-agent-list-hosting-net private
+--------------------------------------+----------------------------------+----------------+-------+
| id | host | admin_state_up | alive |
+--------------------------------------+----------------------------------+----------------+-------+
| f10e63e1-ea10-4897-adc3-7c395b7bbb20 | openstack.eng.lab.tlv.redhat.com | True | :-) |
+--------------------------------------+----------------------------------+----------------+-------+
openstack@openstack:~/devstack$ quantum agent-list
+--------------------------------------+--------------------+-----------------------------------------+-------+----------------+
| id | agent_type | host | alive | admin_state_up |
+--------------------------------------+--------------------+-----------------------------------------+-------+----------------+
| 18cf3f85-3879-497c-833e-0a5bfea38e71 | Open vSwitch agent | openstack.eng.lab.tlv.redhat.com | :-) | True |
| dcc13a1d-9d3c-4b06-ae4c-2263ece97a59 | L3 agent | openstack.eng.lab.tlv.redhat.com | :-) | True |
| dd1a8201-9f24-4b59-be67-310668a6030d | DHCP agent | gkotton-ubuntu12.eng.lab.tlv.redhat.com | :-) | True |
| f10e63e1-ea10-4897-adc3-7c395b7bbb20 | DHCP agent | openstack.eng.lab.tlv.redhat.com | :-) | True |
+--------------------------------------+--------------------+-----------------------------------------+-------+----------------+
openstack@openstack:~/devstack$ quantum dhcp-agent-network-add dd1a8201-9f24-4b59-be67-310668a6030d f10e63e1-ea10-4897-adc3-7c395b7bbb20
Unable to find network with name 'f10e63e1-ea10-4897-adc3-7c395b7bbb20'
openstack@openstack:~/devstack$ quantum dhcp-agent-network-add dd1a8201-9f24-4b59-be67-310668a6030d private
Added network private to DHCP agent
openstack@openstack:~/devstack$ quantum dhcp-agent-list-hosting-net private
+--------------------------------------+-----------------------------------------+----------------+-------+
| id | host | admin_state_up | alive |
+--------------------------------------+-----------------------------------------+----------------+-------+
| dd1a8201-9f24-4b59-be67-310668a6030d | gkotton-ubuntu12.eng.lab.tlv.redhat.com | True | :-) |
| f10e63e1-ea10-4897-adc3-7c395b7bbb20 | openstack.eng.lab.tlv.redhat.com | True | :-) |
+--------------------------------------+-----------------------------------------+----------------+-------+

Does this suffice?

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/27907

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/27907
Committed: http://github.com/openstack/quantum/commit/c95e58b70796eae6bbc8bac283f81df9aa1d1894
Submitter: Jenkins
Branch: master

commit c95e58b70796eae6bbc8bac283f81df9aa1d1894
Author: Gary Kotton <email address hidden>
Date: Wed May 1 12:54:11 2013 +0000

    Enable network to be scheduled to N DHCP agents

    Fixes bug 1174132

    Change-Id: Iabe96fd8a98f3539eb21268fb5ef58df8dbd8782

[Robert Collins (lifeless)]

Wooo! Thanks.

We need to fold this into the tripleO automation to close the tripleo task.

[Robert Collins (lifeless)]

From a tripleo perspective we just need to set 235 # dhcp_agents_per_network = 2 (or three) now.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/74424

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/74424
Committed: https://git.openstack.org/cgit/openstack/tripleo-image-elements/commit/?id=6dd529e01a5bb0df3be4ce518f25968fe8ed416f
Submitter: Jenkins
Branch: master

commit 6dd529e01a5bb0df3be4ce518f25968fe8ed416f
Author: Ryan O'Hara <email address hidden>
Date: Tue Feb 18 10:07:42 2014 -0600

    Update neutron config to use multiple dhcp agents

    Neutron should schedule two dhcp agents per network by default.

    Change-Id: I9775937cc54864fcc1cb95e3015d702b68131830
    Partial-Bug: #1174132