Which do you prefer - a micro-service approach or a monolithic app?

When asking about a preference, the interviewer is seeking to understand how you approach your work. Your response to this question is based on two factors. The first is your experience and skill set in this job. The second is the research you have done about Facebook and your understanding of their preferences for the type of operations they perform. Your answer can either align with Facebook's processes or conflict with them. If you choose to conflict with them, you should be able to rationalize your answer based on your experience.