Architecture of Auto Complete/Type Ahead functionality build on Distributed Tries where the top K terms are dynamic and based on data mining of Current trends/ Top news etc.

Scalable, Web socket based Messaging Application having one to one chatting and file exchange capabilities. It also shows online user and Send/Read message status

Decorator Pattern is a structural design pattern which combines inheritance and Composition.

URL Shortener aka TinyURL comprises an array of worker hosts whose number can be varied as per traffic (Scalable). Used Memcache as a distributed cache for low latencies.

Adapter Pattern is a structural design pattern which bridges gap between two interfaces.

Composite Pattern is a structural design pattern which is used when we need a tree structure to traverse across the object in hierarchical fashion.

Abstract Factory Pattern is a creational design pattern which is also known as Factory of factories.

Factory Pattern is a creational design pattern which doesn't expose instantiation or creation logic and returns new instace when object is asked.

Builder Pattern is a creational design pattern which is used to create immutable objects with default values for attributes.

Singleton Pattern is a creational design pattern which makes sure only a single instance of that class is created and returned each time when a request for an object is made.

OAuth is open standard for access deligation providing client secure delegated access. Its an Authorization Standard.

JWT is a tokenization format in which we pass our credentials and content in a single format wrapped inside token.