hū​zhī​jí​lái​huī​zhī​jí​qù

at someone's beck and call

呼之即来,挥之即去 呼之即來,揮之即去 hū​zhī​jí​lái​huī​zhī​jí​qù
at someone's beck and call
to come when called and leave when dismissed; used to describe being subservient or arbitrarily ordered around by others
ready for action
instantly responsive to orders or instructions; used to describe a disciplined force or readiness to follow commands at any moment