Using a Headless vRouter to Improve Redundancy
Overview: vRouter Agent Redundancy
The Contrail vRouter agent downloads routes, configurations, and the multicast tree from the control node. For redundancy, the vRouter agent connects to two control nodes.
However, in some circumstances, it is possible for the vRouter agent to lose the connection to the two control nodes, in this case, the information provided by the control nodes can get flushed. If the vRouter agent loses connection to the control nodes, the multicast and unicast are flushed immediately, however, the configuration agent waits awhile for the control node to come up, and after that time, the configuration information gets flushed.
Headless vRouter Function
When the headless vRouter feature is enabled, if the agent's connection to the control nodes is lost, the last known information about routes, configurations, and the multicast tree is retained and marked as stale entries. In the mean time, the system can remain in a working state. When the control node comes up again, the agent waits awhile to flush out the stale entries, and the newly-connected control node sends information about the routes, configurations, and multicast tree to the agent.
If the control node is in an unstable state, coming up and going down again, the agent retains the stale information until the control node becomes stable again.
Configuring the Headless vRouter
By default, the vRouter agent runs in non-headless mode. You can enable the headless router feature by using the command-line interface or by configuring the agent configuration file. In headless mode, the vRouter agent retains the last known good configuration from the control node if all control nodes are lost.
Using CLI to Configure Headless vRouter
Use the following command-line parameters to enable the headless vRouter. The following argument will run the compute node in headless mode.
--DEFAULT.headless arg
Using contrail-vrouter-agent.conf to Configure Headless vRouter
Use the following line in the DEFAULT section of the contrail-vrouter-agent.conf to enable the headless vRouter.
headless_mode=true
Possible values include true (enable) and false (disable).
