On RHEL6 and before, we used to use chkconfig to change/disable/enable a target runlevel. What about on RHEL7?

Chkconfig still works on RHEL7, however, eventually it will be replaced by systemd. Here is a quick answer shows you how to do it with systemd

How do I change the target (runlevel)?

systemd has the concept of targets which is a more flexible replacement for runlevels in sysvinit.

Run level 3 is emulated by multi-user.target. Run level 5 is emulated by graphical.target. runlevel3.target is a symbolic link to multi-user.target and runlevel5.target is a symbolic link to graphical.target.

You can switch to 'runlevel 3' by running

 systemctl isolate multi-user.target 

You can switch to 'runlevel 5' by running

 systemctl isolate graphical.target 

How do I change the default target?

 systemctl set-default <name of target>.target 

graphical.target is the default. You might want multi-user.target for the equivalent of non graphical (runlevel 3) from sysv init. The full list of targets can be accessed via systemctl list-units --type=target

systemd does not use /etc/inittab file.

How do I know the current target?

 systemctl get-default