What are the round brown dome looking insects I can see on the underside and mid-rib of my Palms/Cycads?

scale

These are scale. Another sucking insect attracted to Palms and Cycads.

How to control?

These insects can be controlled by using a horticultural oil as a spray such as Sunoil. A gentler, organic alternative would be a canola or soya oil. The oil works by suffocating the scale insect.