One need to understand these basic concepts for system designing

DNS: domain name system

APIs has Restful and GraphQL two types

CAP Theorem

Websocket

Webhook

Monolithic Architecture versus Microservices

Message Queues

Elastic Search: stores data in JSON documents (kind of like a flexible NoSQL database); It builds a structure called an inverted index — think of it like a book index on steroids that knows every word and where it appears; It supports full-text search, filters, sorting, relevance ranking, fuzzy match (typo-tolerance), and aggregations (mini analytics)

Elasticsearch is built on top of Apache Lucene, which is also Java-based. Lucene is a powerful, low-level search library, and Elasticsearch gives it a user-friendly, scalable API.

API Gateway

Redis: