First HLD of Notification System, then question based on it like
How would you ensure that each notification is sent exactly once to each user?
Which design pattern would you apply in this scenario?
How would you handle time based or scheduled notifications?
You have an Order Service that interacts with three microservices - Payments, Inventory, and Receipt Generation. If the payment fails, how would you handle partial updates, money deduction, and rollback scenarios to maintain consistency?