InterviewBit Problems   Design Twitter

How many tweets should we fetch at a time? (4)
Also the approach retained using Shard on recency( timestamp ) is so wrong. So al (1)
Question: Approach1: How can we shard on users? (3)
How can we handle a DB machine going down? (1)
How will you take care of application layer fault tolerance? (1)
Design Twitter How does our client know which application servers to talk to. How does it know which application servers have gone down and which ones are still working? (3)