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  Java Spring framework is one of the popular java frameworks. A thread on 5 commonly used spring modules 1. Spring Boot and Spring MVC These modules makes it easy and quick to create stand-alone, production-grade Spring based Applications that you can "just run". Example Use:- A RESTful service with self-container server. 2. Spring Batch This module is used to build batch applications that need to recurrently process large volumes of data. Features: Chunk based processing, retry, skip Example Use:- Everyday, read data of daily trades from database and update the credit on customer's accounts. 3.Spring Data Provides a spring based programming model for accessing data. This module has very powerful features and supports wide range of databases. Example Use:- Read, Write data from PostgreSQL for your application. 4.Spring Cloud Provides tools for developers to quickly build some of the common patterns of distributed systems. Libraries for Service registration and discovery,

When designing a system, you need to choose an appropriate database based on the use cases and other considerations. Sharing an insightful article by  Satish Chandra Gupta  on this topic. Do read to improve your knowledge on databases https://towardsdatascience.com/datastore-choices-sql-vs-nosql-database-ebec24d56106  

  5 important aspects/components of microservices architecture 1. Microservices - Services that are built small enough so that their entire lifecycle can be owned and managed by a small team. 2. Service Discovery - A mechanism of how microservices can locate each other over network.  Example : if Microservice A wants to call microservice B:  It will use service discovery mechanism to fetch IP address and port of B and then call B. Implementations : ZooKeeper, Consul, etcd, Eureka 3. External configuration - Enable services to run on various environments without a code modification inside the service. Enable different configuration values for those services for different environments.  Dynamically change configurations without changing application code or restart/redeploy application. Example - DB credentials and other details, application properties, environment variables for Dev, QA and Prod env. Implementations : Consul, Spring cloud (enables various datastores to store needed con