how to design data layer as a k8s service

I have a design challenge and would like to get some expert advice. I am planning to design a data layer as a k8s service which our UI will invoke. The data layer needs to get the data from two different PostGres DB instances. How should I design the layer? Can elasticsearch help me here? Which technology stack I should use?

Is there any push mechanism from PostGres DB if there in any change is the DB table rather than periodically pull by the data layer?