Used as a translation of the English phrase rather than an actual phrase used in Vietnamese proper.
When seeing each other in the morning, Vietnamese speakers would probably say something like dậysớmvậy/thế/ha(“you sure woke up early”), dậyrồihả/à?(“you're up already?”), ngủngonkhông?(“good sleep last night?”)(if it is early morning) or just casual greetings like khoẻkhông?(“how are you”) and chào (if it is later in the morning). If one really wants to say something akin to English "good morning", buổi sángtốt lành/an lành might be fitting but even this still sounds pretty stiff/artificial (more common in texts or emails than colloquial speech).