Agents and Services¶
A usual neutron setup consists of multiple services and agents running on one or multiple nodes (though some setups may not need any agents). Each of these services provide some of the networking or API services. Among those of special interest are:
The neutron-server that provides API endpoints and serves as a single point of access to the database. It usually runs on the controller nodes.
Layer2 agent that can utilize Open vSwitch, Linux Bridge or other vendor-specific technology to provide network segmentation and isolation for project networks. The L2 agent should run on every node where it is deemed responsible for wiring and securing virtual interfaces (usually both compute and network nodes).
Layer3 agent that runs on network node and provides east-west and north-south routing plus some advanced services such as FWaaS or VPNaaS.
Configuration options¶
The neutron configuration options are segregated between
neutron-server and agents. Both services and agents may load the main
neutron.conf since this file should contain the oslo.messaging
configuration for internal neutron RPCs and may contain host specific
configuration, such as file paths. The neutron.conf contains the
database, keystone, nova credentials, and endpoints strictly for
neutron-server to use.
In addition, neutron-server may load a plugin-specific configuration file, yet the agents should not. As the plugin configuration is primarily site wide options and the plugin provides the persistence layer for neutron, agents should be instructed to act upon these values through RPC.
Each individual agent may have its own configuration file. This file should be
loaded after the main neutron.conf file, so the agent configuration takes
precedence. The agent-specific configuration may contain configurations which
vary between hosts in a neutron deployment such as the local_ip for an L2
agent. If any agent requires access to additional external services beyond the
neutron RPC, those endpoints should be defined in the agent-specific
configuration file (for example, nova metadata for metadata agent).
Agent’s admin state specific config options¶
When creating a new agent the admin_state_up field will be set to the
value of enable_new_agents config option, the default value of this config
option is true:
[DEFAULT]
enable_new_agents = true
It is possible to set the admin_state_up value of an agent to False
via the API, or CLI:
$ openstack network agent set agent-uuid --disable
The effect of this varies by agent type:
L2 agents¶
The admin_state_up field of the agent in the Neutron database is set to
False, but the agent is still capable of binding ports.
This is true for openvswitch-agent, linuxbridge-agent, and sriov-agent.
Note
In case of OVN based deployment Neutron doesn’t keep track of OVN
controllers in the agents db table, so setting the admin_state_up
is not allowed as Neutron has no control over OVN entities.
The possiblity to delete an OVN agent via Neutron REST API, is to clean
up bad chassis information.
Metadata agent¶
Setting admin_state_up to False has no effect to the Metadata agent.
DHCP agent¶
DHCP agent scheduler will schedule networks to agents whose admin_state_up
is True.
L3 agent¶
L3 scheduler will schedule routers to L3 agents whose admin_state_up field
is True.
External processes run by agents¶
Some neutron agents, like DHCP, Metadata or L3, often run external
processes to provide some of their functionalities. It may be keepalived,
dnsmasq, haproxy or some other process.
Neutron agents are responsible for spawning and killing such processes when
necessary. By default, to kill such processes, agents use a simple kill
command, but in some cases, like for example when those additional services
are running inside containers, it may be not a good solution.
To address this problem, operators should use the AGENT config group option
kill_scripts_path to configure a path to where kill scripts for such
processes live. By default, it is set to /etc/neutron/kill_scripts/.
If option kill_scripts_path is changed in the config to the different
location, exec_dirs in /etc/rootwrap.conf should be changed accordingly.
If kill_scripts_path is set, every time neutron has to kill a process,
for example dnsmasq, it will look in this directory for a file with the name
<process_name>-kill. So for dnsmasq process it will look for a
dnsmasq-kill script. If such a file exists there, it will be called
instead of using the kill command.
Kill scripts are called with two parameters:
<process>-kill <sig> <pid>
where: <sig> is the signal, same as with the kill command, for example
9 or SIGKILL; and <pid> is pid of the process to kill.
This external script should then handle killing of the given process as neutron
will not call the kill command for it anymore.
