Shrimad Bhagwat Geeta, Manusmriti and many other Vedic texts mention about preferred occupations of the four varnas.
According to Vedic astrology, rashis are classified in the four varnas.
Shudra: People belonging to Shudra rashis are assumed to be physically stronger than those belonging to other rashis. Therefore, labour intensive works are suggested for them.
Vaishya: Their physical strength is assumed to be lesser than that of shudras. Therefore, occupations like trading and agriculture which require a bit lesser physical strength, are suggested for Vaishya rashis.
Kshatriya: Physical strength of Kshatriyas is supposed to be lesser than the above two classes. Therefore, administrative jobs such as king, Minister etc. are suggested for these rashis.
Brahmin: These rashis assumed to be physically weakest among all classes have been suggested the occupations of teacher, reader etc. which require minimum application of physical strength.