KUBERNETES API supports two types of selectors:
Equality-based selectors - It allows filtering using label keys and values. There are three kinds of operators for equality-based selectors: =, ==, !=.
For example: environment = test
set-based selectors - It allows filtering using keys according to a set of values. There are three kinds of operators for set-based selectors: notin, in, exists.
For example: environment in (test)