I was interviewed recently for FB onsite system design in Dec 2021 for singapore location. I have 10+ years of exp.

Design privacy for a FB post
Users will select three privacy options in a post.

1. Public
2. Friends
3. Friends of Friends
   After the user selects any privacy option others will view the post based on the post privacy setting.

I clarified questions about this requirement.

• no of daily active users
• no of read/writes etc
• non-functional requirements (availability, latency, read/write ratio, scalability etc)

After writing func/non-func req and scale.

• Draw high level design.
• APIs /get-privacy-settings, /post-message, /check-privacy etc
• DB tables user_post, user_friends

Then interviewer asked few cross-questions. I managed to ans.

• how will you handle friends-of-friends check for a post
• how will you handle new privacy types (group, exclude, include particular persons etc)
• why I choosen user_friends table and how data look like.
• discussed special case about celebrity users.

It all felt ok in dicussions...
later got rejected due to f***ed up on a Coding round :)

Got feedback about Product Design-

• communication, discussion all good
• should also consider quantitative analysis. like always calculate on each decision data volume, no of users, read/write and have these numbers drive your conversation.
• I felt for each question interviewer asks you should ans it 2-3 steps each going deeper (onion like explanation step by step) and don't ans 1 liner.

Going to work more on these and hope to crack any FAANG soon :)

Good Luck 🍀 Everyone !!
Lets Enjoy this journey together.....