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Topics mentioned in the video:
Functional (create topic, publish message, subscribe to a topic) and nonfunctional (high scalability, high availability, high performance, durability) requirements.
Highlevel architecture of a notification service.
FrontEnd service host components (reverse proxy, local cache, logs and metrics agents).
Metadata service, distributed cache, consistent hashing ring, gossip protocol.
Storage for messages: SQL/NoSQL database, inmemory store, distributed message queue, streamprocessing platform.
Message sender service, thread pool, semaphore.
Duplicate messages, retry policy, message order, security, monitoring.

Inspired by the following interview questions:
Amazon (https://www.careercup.com/question?id...)
Flipkart (https://www.careercup.com/question?id...)
Microsoft (https://www.careercup.com/question?id...)
Uber (https://www.careercup.com/question?id...)