Event Details

Neutron's Router presents a L3 interface that connects VMs to an external network. In its legacy mode, a router can be scheduled only to one agent at a time, presenting a single point of failure - if that node fails, all communications are halted. L3 HA mitigates this issue by presenting an Active/Passive configuration where a router can be scheduled to multiple agents which recover the datapath automatically during failures using a dedicated network that hosts keepalived processes.

Using L3 HA presents an orchestration problem: since a router now appears in more than one agent and another dedicated network is required for the keepalived processes, there are a lot more resources involved. We performed L3 HA scale testing for Liberty and Mitaka, which showed benefits of L3 HA and uncovered a number of race conditions in Neutron code both on L3 agent and on server side. We'll present results of this scale testing and showcase some of these race conditions.