Module 1
Web Application & Software Architecture
Two software design principles that are key to explaining this are the Single Responsibility Principle(one responsibility to a component & letting it execute it with perfection) & the Separation of Concerns(be concerned about your work only & stop worrying about the rest of the stuff.)
The layers mentioned in the illustration are at the code level. The difference between layers and tiers is that the layers represent the organization of the code and breaking it into components. Whereas, tiers involve physical separation of components.

Web Architecture
Clients:
Thin clients: Thin Client is the client which holds just the user interface of the application. It has no business logic
Thick clients: On the contrary, the thick client holds all or some part of the business logic.(2 tiers, such as gaming etc)

Server:
The primary task of a web server is to receive the requests from the client & provide the response after executing the business logic based on the request parameters received from the client.
REST stands for Representational State Transfer. It’s a software architectural style for implementing web services. Web services implemented using the REST architectural style are known as the RESTful Web services.

http pull: The client pulls the data from the server whenever it requires.
http push: client sends the request for particular information to the server, just for the first time, & after that the server keeps pushing the new updates to the client whenever they are available.
HTTP push-base tech
A Web Socket connection is ideally preferred when we need a persistent bi-directional low latency data flow from the client to server & back. (chat etc)