As it turns out, InstantCommons feature relies on curl extension or fopen wrapper . If user have completed the installation without HTTP external connector, user will be very confused, why InstantCommons does not work.
We can check the environment at the same time check PHP is loaded with curl extension or enabled allow_url_fopen option. If missing HTTP external connector, installer prompts missing HTTP external connector but does not affect the installation. And users cannot enable InstantCommons later in the installation step.