The OpenStack Juno release comes with a feature that brings closer parity with the legacy nova-network called Distributed Virtual Routers (DVR). This feature allows L3 Routers to be distributed across our Compute hosts, in the same way as the nova-network feature, and thus provide high availability of this important routing feature. The result is that each instance attaches to the router located on the Compute host, rather than a central point on the network nodes. This is an acceptable HA failure scenario; if a Compute host fails (and therefore that router), it only affects the instances running on that Compute host.
The following figure shows the environment used in this chapter, but our Compute hosts are now running the L3 Agent. We also utilize the
eth3 interface and the external bridge,
br-ex, to our Compute host. This interface wasn't needed in a Legacy L3 Router environment but, for a DVR-enabled Compute host, we are adding in the capabilities...