Scalable and highly available DHCP agents

updated: 2015-10-12 18:28 | release: 0.9
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Contents

Scalable and highly available DHCP agents

This section describes how to use the agent management (alias agent) and scheduler (alias agent_scheduler) extensions for DHCP agents scalability and HA.

Note

Use the neutron ext-list client command to check if these extensions are enabled:

$ neutron ext-list -c name -c alias

+-----------------+--------------------------+
| alias           | name                     |
+-----------------+--------------------------+
| agent_scheduler | Agent Schedulers         |
| binding         | Port Binding             |
| quotas          | Quota management support |
| agent           | agent                    |
| provider        | Provider Network         |
| router          | Neutron L3 Router        |
| lbaas           | Load Balancing service    |
| extraroute      | Neutron Extra Route      |
+-----------------+--------------------------+

image0

There will be three hosts in the setup.

Host Description
OpenStack controller host - controlnod Runs the Networking, Identity, and Compute services that are required to deploy VMs. The node must have at least one network interface that is connected to the Management Network. Note that nova-network should not be running because it is replaced by Neutron.
HostA Runs nova-compute, the Neutron L2 agent and DHCP agent
HostB Same as HostA

Hosts for demo

Configuration

controlnode: neutron server

  1. Neutron configuration file /etc/neutron/neutron.conf:

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     [DEFAULT]
 core_plugin = linuxbridge
 rabbit_host = controlnode
 allow_overlapping_ips = True
 host = controlnode
 agent_down_time = 5

  2. Update the plug-in configuration file /etc/neutron/plugins/linuxbridge/linuxbridge_conf.ini:

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     [vlans]
 tenant_network_type = vlan
 network_vlan_ranges = physnet1:1000:2999
 [database]
 connection = mysql://root:root@127.0.0.1:3306/neutron_linux_bridge
 retry_interval = 2
 [linux_bridge]
 physical_interface_mappings = physnet1:eth0

HostA and HostB: L2 agent

  1. Neutron configuration file /etc/neutron/neutron.conf:

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     [DEFAULT]
 rabbit_host = controlnode
 rabbit_password = openstack
 # host = HostB on hostb
 host = HostA

  2. Update the plug-in configuration file /etc/neutron/plugins/linuxbridge/linuxbridge_conf.ini:

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     [vlans]
 tenant_network_type = vlan
 network_vlan_ranges = physnet1:1000:2999
 [database]
 connection = mysql://root:root@127.0.0.1:3306/neutron_linux_bridge
 retry_interval = 2
 [linux_bridge]
 physical_interface_mappings = physnet1:eth0

  3. Update the nova configuration file /etc/nova/nova.conf:

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     [DEFAULT]
 network_api_class=nova.network.neutronv2.api.API
 firewall_driver=nova.virt.firewall.NoopFirewallDriver

 [neutron]
 admin_username=neutron
 admin_password=servicepassword
 admin_auth_url=http://controlnode:35357/v2.0/
 auth_strategy=keystone
 admin_tenant_name=servicetenant
 url=http://100.1.1.10:9696/

HostA and HostB: DHCP agent

  • Update the DHCP configuration file /etc/neutron/dhcp_agent.ini:

    [DEFAULT]
interface_driver = neutron.agent.linux.interface.BridgeInterfaceDriver

Commands in agent management and scheduler extensions

The following commands require the tenant running the command to have an admin role.

Note

Ensure that the following environment variables are set. These are used by the various clients to access the Identity service.

export OS_USERNAME=admin
export OS_PASSWORD=adminpassword
export OS_TENANT_NAME=admin
export OS_AUTH_URL=http://controlnode:5000/v2.0/

Settings

To experiment, you need VMs and a neutron network:

$ nova list

 +-------------------------------------+----------+--------+--------------+
 | ID                                  | Name     | Status | Networks     |
 +-------------------------------------+----------+--------+--------------+
 | c394fcd0-0baa-43ae-a793-201815c3e8ce| myserver1| ACTIVE | net1=10.0.1.3|
 | 2d604e05-9a6c-4ddb-9082-8a1fbdcc797d| myserver2| ACTIVE | net1=10.0.1.4|
 | c7c0481c-3db8-4d7a-a948-60ce8211d585| myserver3| ACTIVE | net1=10.0.1.5|
 +-------------------------------------+----------+--------+--------------+

$ neutron net-list
 +-------------------------+------+--------------------------------------+
 | id                      | name | subnets                              |
 +-------------------------+------+--------------------------------------+
 | 89dca1c6-c7d4-4f7a-     |      |                                      |
 | b730-549af0fb6e34       | net1 | f6c832e3-9968-46fd-8e45-d5cf646db9d1 |
 +-------------------------+------+--------------------------------------+

Manage agents in neutron deployment

Every agent that supports these extensions will register itself with the neutron server when it starts up.

  1. List all agents:

    $ neutron agent-list

+--------------------------------------+--------------------+-------+-------+----------------+
| id                                   | agent_type         | host  | alive | admin_state_up |
+--------------------------------------+--------------------+-------+-------+----------------+
| 1b69828d-6a9b-4826-87cd-1757f0e27f31 | Linux bridge agent | HostA | :-)   | True           |
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | DHCP agent         | HostA | :-)   | True           |
| ed96b856-ae0f-4d75-bb28-40a47ffd7695 | Linux bridge agent | HostB | :-)   | True           |
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | DHCP agent         | HostB | :-)   | True           |
+--------------------------------------+--------------------+-------+-------+----------------+

    The output shows information for four agents. The alive field shows :-) if the agent reported its state within the period defined by the agent_down_time option in the neutron.conf file. Otherwise the alive is xxx.

  2. List the DHCP agents that host a specified network:

    In some deployments, one DHCP agent is not enough to hold all network data. In addition, you must have a backup for it even when the deployment is small. The same network can be assigned to more than one DHCP agent and one DHCP agent can host more than one network.

  3. List DHCP agents that host a specified network:

    $ neutron dhcp-agent-list-hosting-net net1

+--------------------------------------+-------+----------------+-------+
| id                                   | host  | admin_state_up | alive |
+--------------------------------------+-------+----------------+-------+
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | HostA | True           | :-)   |
+--------------------------------------+-------+----------------+-------+

  4. List the networks hosted by a given DHCP agent:

    This command is to show which networks a given dhcp agent is managing.

    $ neutron net-list-on-dhcp-agent a0c1c21c-d4f4-4577-9ec7-908f2d48622d

+------------------------+------+---------------------------------+
| id                     | name | subnets                         |
+------------------------+------+---------------------------------+
| 89dca1c6-c7d4-4f7a     |      |                                 |
| -b730-549af0fb6e34     | net1 | f6c832e3-9968-46fd              |
|                        |      | -8e45-d5cf646db9d1  10.0.1.0/24 |
+------------------------+------+---------------------------------+

  5. Show agent details.

    The agent-show command shows details for a specified agent:

    $ neutron agent-show a0c1c21c-d4f4-4577-9ec7-908f2d48622d

+--------------------+---------------------------------------------------+
| Field              | Value                                             |
+--------------------+---------------------------------------------------+
| admin_state_up     | True                                              |
| agent_type         | DHCP agent                                        |
| alive              | False                                             |
| binary             | neutron-dhcp-agent                                |
| configurations     |{                                                  |
|                    | "subnets": 1,                                     |
|                    | "use_namespaces": true,                           |
|                    | "dhcp_driver": "neutron.agent.linux.dhcp.Dnsmasq",|
|                    | "networks": 1,                                    |
|                    | "dhcp_lease_time": 120,                           |
|                    | "ports": 3                                        |
|                    |}                                                  |
| created_at         | 2013-03-16T01:16:18.000000                        |
| description        |                                                   |
| heartbeat_timestamp| 2013-03-17T01:37:22.000000                        |
| host               | HostA                                             |
| id                 | 58f4ce07-6789-4bb3-aa42-ed3779db2b03              |
| started_at         | 2013-03-16T06:48:39.000000                        |
| topic              | dhcp_agent                                        |
+--------------------+---------------------------------------------------+

    In this output, heartbeat_timestamp is the time on the neutron server. You do not need to synchronize all agents to this time for this extension to run correctly. configurations describes the static configuration for the agent or run time data. This agent is a DHCP agent and it hosts one network, one subnet, and three ports.

    Different types of agents show different details. The following output shows information for a Linux bridge agent:

    $ neutron agent-show ed96b856-ae0f-4d75-bb28-40a47ffd7695

+---------------------+--------------------------------------+
| Field               | Value                                |
+---------------------+--------------------------------------+
| admin_state_up      | True                                 |
| binary              | neutron-linuxbridge-agent            |
| configurations      | {                                    |
|                     |      "physnet1": "eth0",             |
|                     |      "devices": "4"                  |
|                     | }                                    |
| created_at          | 2013-03-16T01:49:52.000000           |
| description         |                                      |
| disabled            | False                                |
| group               | agent                                |
| heartbeat_timestamp | 2013-03-16T01:59:45.000000           |
| host                | HostB                                |
| id                  | ed96b856-ae0f-4d75-bb28-40a47ffd7695 |
| topic               | N/A                                  |
| started_at          | 2013-03-16T06:48:39.000000           |
| type                | Linux bridge agent                   |
+---------------------+--------------------------------------+

    The output shows bridge-mapping and the number of virtual network devices on this L2 agent.

Manage assignment of networks to DHCP agent

Now that you have run the net-list-on-dhcp-agent and dhcp-agent-list-hosting-net commands, you can add a network to a DHCP agent and remove one from it.

  1. Default scheduling.

    When you create a network with one port, you can schedule it to an active DHCP agent. If many active DHCP agents are running, select one randomly. You can design more sophisticated scheduling algorithms in the same way as nova-schedule later on.

    $ neutron net-create net2
$ neutron subnet-create net2 9.0.1.0/24 --name subnet2
$ neutron port-create net2
$ neutron dhcp-agent-list-hosting-net net2

+--------------------------------------+-------+----------------+-------+
| id                                   | host  | admin_state_up | alive |
+--------------------------------------+-------+----------------+-------+
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | HostA | True           | :-)   |
+--------------------------------------+-------+----------------+-------+

    It is allocated to DHCP agent on HostA. If you want to validate the behavior through the dnsmasq command, you must create a subnet for the network because the DHCP agent starts the dnsmasq service only if there is a DHCP.

  2. Assign a network to a given DHCP agent.

    To add another DHCP agent to host the network, run this command:

    $ neutron dhcp-agent-network-add f28aa126-6edb-4ea5-a81e-8850876bc0a8 net2
Added network net2 to dhcp agent
$ neutron dhcp-agent-list-hosting-net net2

+--------------------------------------+-------+----------------+-------+
| id                                   | host  | admin_state_up | alive |
+--------------------------------------+-------+----------------+-------+
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | HostA | True           | :-)   |
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | HostB | True           | :-)   |
+--------------------------------------+-------+----------------+-------+

Both DHCP agents host the ``net2`` network.

  3. Remove a network from a specified DHCP agent.

    This command is the sibling command for the previous one. Remove net2 from the DHCP agent for HostA:

    $ neutron dhcp-agent-network-remove a0c1c21c-d4f4-4577-9ec7-908f2d48622d
net2
Removed network net2 to dhcp agent
$ neutron dhcp-agent-list-hosting-net net2

+--------------------------------------+-------+----------------+-------+
| id                                   | host  | admin_state_up | alive |
+--------------------------------------+-------+----------------+-------+
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | HostB | True           | :-)   |
+--------------------------------------+-------+----------------+-------+

    You can see that only the DHCP agent for HostB is hosting the net2 network.

HA of DHCP agents

Boot a VM on net2. Let both DHCP agents host net2. Fail the agents in turn to see if the VM can still get the desired IP.

  1. Boot a VM on net2:

    $ neutron net-list

+-------------------------+------+-----------------------------+
| id                      | name | subnets                     |
+-------------------------+------+-----------------------------+
| 89dca1c6-c7d4-4f7a-     |      |                             |
| b730-549af0fb6e34       | net1 | f6c832e3-9968-46fd-8e45     |
|                         |      | -d5cf646db9d1  10.0.1.0/24  |
| 9b96b14f-71b8-4918-90aa-|      |                             |
| c5d705606b1a            | net2 | 6979b71a-0ae8-448c-aa87-    |
|                         |      | 65f68eedcaaa  9.0.1.0/24    |
+-------------------------+------+-----------------------------+

    $ nova boot --image tty --flavor 1 myserver4 \
  --nic net-id=9b96b14f-71b8-4918-90aa-c5d705606b1a

       $ nova list

+-------------------------------------+----------+-------+---------------+
| ID                                  | Name     | Status| Networks      |
+-------------------------------------+----------+-------+---------------+
|c394fcd0-0baa-43ae-a793-201815c3e8ce |myserver1 |ACTIVE | net1=10.0.1.3 |
|2d604e05-9a6c-4ddb-9082-8a1fbdcc797d |myserver2 |ACTIVE | net1=10.0.1.4 |
|c7c0481c-3db8-4d7a-a948-60ce8211d585 |myserver3 |ACTIVE | net1=10.0.1.5 |
|f62f4731-5591-46b1-9d74-f0c901de567f |myserver4 |ACTIVE | net2=9.0.1.2  |
+-------------------------------------+----------+-------+---------------+

  2. Make sure both DHCP agents hosting ‘net2’:

    Use the previous commands to assign the network to agents.

    $ neutron dhcp-agent-list-hosting-net net2

+--------------------------------------+-------+----------------+-------+
| id                                   | host  | admin_state_up | alive |
+--------------------------------------+-------+----------------+-------+
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | HostA | True           | :-)   |
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | HostB | True           | :-)   |
+--------------------------------------+-------+----------------+-------+

Test the HA

  1. Log in to the myserver4 VM, and run udhcpc, dhclient or other DHCP client.
  2. Stop the DHCP agent on HostA. Besides stopping the neutron-dhcp-agent binary, you must stop the dnsmasq processes.
  3. Run a DHCP client in VM to see if it can get the wanted IP.
  4. Stop the DHCP agent on HostB too.
  5. Run udhcpc in the VM; it cannot get the wanted IP.
  6. Start DHCP agent on HostB. The VM gets the wanted IP again.

Disable and remove an agent

An administrator might want to disable an agent if a system hardware or software upgrade is planned. Some agents that support scheduling also support disabling and enabling agents, such as L3 and DHCP agents. After the agent is disabled, the scheduler does not schedule new resources to the agent. After the agent is disabled, you can safely remove the agent. Remove the resources on the agent before you delete the agent.

To run the following commands, you must stop the DHCP agent on HostA.

$ neutron agent-update --admin-state-up False a0c1c21c-d4f4-4577
  -9ec7-908f2d48622d
$ neutron agent-list

+--------------------------------------+--------------------+-------+-------+----------------+
| id                                   | agent_type         | host  | alive | admin_state_up |
+--------------------------------------+--------------------+-------+-------+----------------+
| 1b69828d-6a9b-4826-87cd-1757f0e27f31 | Linux bridge agent | HostA | :-)   | True           |
| a0c1c21c-d4f4-4577-9ec7-908f2d48622d | DHCP agent         | HostA | :-)   | False          |
| ed96b856-ae0f-4d75-bb28-40a47ffd7695 | Linux bridge agent | HostB | :-)   | True           |
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | DHCP agent         | HostB | :-)   | True           |
+--------------------------------------+--------------------+-------+-------+----------------+

$ neutron agent-delete a0c1c21c-d4f4-4577-9ec7-908f2d48622d
Deleted agent: a0c1c21c-d4f4-4577-9ec7-908f2d48622d
$ neutron agent-list

+--------------------------------------+--------------------+-------+-------+----------------+
| id                                   | agent_type         | host  | alive | admin_state_up |
+--------------------------------------+--------------------+-------+-------+----------------+
| 1b69828d-6a9b-4826-87cd-1757f0e27f31 | Linux bridge agent | HostA | :-)   | True           |
| ed96b856-ae0f-4d75-bb28-40a47ffd7695 | Linux bridge agent | HostB | :-)   | True           |
| f28aa126-6edb-4ea5-a81e-8850876bc0a8 | DHCP agent         | HostB | :-)   | True           |
+--------------------------------------+--------------------+-------+-------+----------------+

After deletion, if you restart the DHCP agent, it appears on the agent list again.

updated: 2015-10-12 18:28 | release: 0.9
suggest edits
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