Support for basic L3HA has landed U/S in both ovn (ovs 2.8) and neworking-ovn (Queens) mechanism driver. But we need to polish it and add support to let the admin discover which controller is the master through the API (without looking at the SBDB manually).
An idea we just discussed was extending the northbound database with a simple boolean on the Gateway_Chassis table to reflect if it's the current master or not. That information is already available through the southbound database by examining the Port_Binding table, but doing something in the northbound db would be a usability improvement. One catch is that the current db schema allows you to reference a single Gateway_Chassis for multiple gateways, so maybe putting the column on Gateway_Chassis doesn't work. Another option could be a new column on Logical_Router_Port that references a single gateway_chassis row to indicate which is the current master.
*** This bug has been marked as a duplicate of bug 1433532 ***