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.

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.

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

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.