Services and agents

Services and agents

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:

  1. 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.
  2. 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).
  3. 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 external_network_bridge for an L3 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).

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